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THORACOSCOPIC PULMONARY BIOPSY:
TECHNIQUE AND SAFETY IN HORSES
presented by

JOEL LUGO, DVM

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of the requirements for

MASTER degree in LARGE ANIMAL
CLINICAL SCIENCES

 

 

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6/01 cleIRC/DateDquSS-p. 15

 

THORACOSCOPIC PULMONARY BIOPSY: TECHNIQUE AND SAFETY
IN HORSES
By

Joel Lugo, DVM

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Large Animal Clinical Sciences

2002

ABSTRACT
THORACOSCOPIC PULMONARY BIOPSY: TECHNIQUE AND SAFETY
IN HORSES
By

Joel Lugo, DVM

Thoracoscopic surgery has replaced many of the open thoracotomy procedures
performed on humans and is beginning to replace some of the same procedures in horses.
Thoracoscopy has been proven safe in healthy horses. However, studies aimed at
determining the usefulness of thoracosc0pic lung biopsy cannot be found. The purpose of
the present study is to investigate the physiological changes and safety of
thoracoscopically guided pulmonary biopsy as a technique for lung biopsy in normal
horses and horses affected with chronic lung disease. Ten horses underwent a
thoracoscopic lung biopsy. During and after surgery, physiological parameters were
measured to evaluate the hemodynamic and cardiopulmonary consequences of the
procedure. All horses underwent a second thoracoscopy fourteen days after lung biopsy
to evaluate the thorax. Biopsy samples were assessed subjectively by histopathology.

The procedure was well tolerated and biopsy specimens adequate for
histopathological examination were successfully obtained in all the horses. A transient
hypoxemia noticed immediately after lung biopsy was probably caused by mismatching
of ventilation and perfusion as a result of pneumothorax. Thoracoscopically guided
pulmonary biopsy provided a minimally invasive and effective method to obtain lung

biopsy specimens in horses.

To my wife, Carmen
for her magnificent devotion to our family
To my parents, J osé and Lucy
for teaching me the principles of life
To my son, Joel Andres
you make my life worthwhile

iii

ACKNOWLEDGEMENT

I gratefully thank my advisor, Dr. N. Edward Robinson, for his continued patience
and support in helping me be successful in completing this task.

I thank my mentors, Dr. John A. Stick and Dr. Frederik J. Derksen, for their
guidance during this project and throughout my residency program.

My sincere gratitude goes to Cathy Berney, Dr. George Bohart, and Dr. Case
Comelisse for the technical support and to Victoria Hoelzer Maddox for the technical
assistance in formatting the thesis.

I thank Ethicon Endo-Surgery, Inc. for donation of the instruments.

iv

TABLE OF CONTENTS

LIST OF TABLES ........................................................................... vii
LISTOF FIGURES ........................................................................... viii
INTRODUCTION ........................................................................... 1
CHAPTER 1
LITERATURE REVIEW .................................................................. 4
Thoracoscopy in humans ........................................................... 4
Historical perspective ...................................................... 4
Basic concepts of thoracoscopy .......................................... 6
Physiologic effects associated with thoraCOSCOpy ..................... 8
Thoracoscopic pulmonary biOpsy ....................................... ll
Thoracoscopy in veterinary medicine ........................................... 13
Lung biopsy .......................................................................... 17
Heaves ................................................................................ 21
Introduction ................................................................. 21
Etiology ..................................................................... 22
Clinical signs ............................................................... 24
Pathophysiology ............................................................ 25
Pathogenesis ................................................................ 25
Pathology .................................................................... 27
Diagnosis .................................................................... 30
Treatment ................................................................... 32
Reasons for using heaves-affected horses in this research ..................... 34
Summary ............................................................................. 35
References for chapter 1 ........................................................... 37
CHAPTER 2
THORACOSCOPY PULMONARY BIOPSY: TECHNIQUE AND SAFETY IN
HORSES ...................................................................................... 47
Summary ............................................................................. 47
Introduction ......................................................................... 48
Materials and Methods ............................................................ 50
Horses ................................................................................ 50
Cardiopulmonary fimction ................................................ 51
Experimental design ....................................................... 52
Surgical procedure ......................................................... 54
Tissue processing .......................................................... 56
Statistical analysis ......................................................... 5 7
Results ................................................................................ 57
Pulmonary function ........................................................ 58

Cardiovascular fimction ...................................................
Post operative evaluation ..................................................
Biopsy samples and histopathology .....................................
2“d Thoracoscopy: 14-day follow-up ....................................
Discussion ...........................................................................
Manufacturer's addresses ..........................................................
References for Chapter 2 ...........................................................

SUMMARY, CONCLUSIONS AND FUTURE INVESTIGATIONS ...............

vi

59
59
6O
61
62
68
69

86

Table 1

LIST OF TABLES

Total differential white blood cell count. packed cell volume.
total protein, PaOz. PC02, and pH before surgery (baseline).
2 hours after surgery, 48 hours after surgery, and 14 days
after surgery for both groups of horses (controls and heaves.)
Data are means i Sd.; * significantly different (p < 0.05)
from baseline; + Significantly different (p < 0.05) between
groups.

vii

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

LIST OF FIGURES

Diagram showing the position of portals to perform a
thoracoscopic pulmonary wedge resection in a horse. 151 portal.
telescope portal, intercostal Space 13h ventral to epaxial
muscles, 2nd portal: endoscopic staple/cutter; intercostal spaces
1] or 12 about 15 cm ventral to first portal, and 3rd portal:
atraumatic Babcock forceps, intercostals space 15, 10 cm
ventral to the ISI portal; dark circle represents the selected site
for lung biopsy.

Technique for thoracoscopic pulmonary wedge resection. Top
left: The biopsy Site is grasped with atraumatic Babcock
forceps; Top right: Endoscopic staple/cutter crossed over and
clamped the pulmonary wedge; Bottom left: Biopsy sample
obtained after pulmonary wedge resection; Bottom right:
Pulmonary site after wedge resection showing good hemostasis.

Effects of detomidine and thoracoscopic lung biopsy on
respiration rate, PaOz, PaCOg, and arterial pH. Data are
expressed at mean : s.e.m; * = significantly difference (p<0.05)
from baseline; 1 = significantly difference (p<0.05) between
groups. Grey bars = control animals, dark bars = heaves-
affected horses. Immediately after the biopsy (post biopsy),
mean PaOz decreased significantly and became lower than at
baseline, after sedation, after pneumothorax and before biopsy.
Once the lung was re- -inflated PaO; increased significantly and
was no longer different from baseline

Effects of thoracoscopic lung biopsy on mean heart rate and
systemic and pulmonary arterial pressures. Data are expressed
at mean : s.e.m.; * = significantly difference (p<0.05) from
baseline; 1 = significantly difference (p<0.05) between groups.
Gray bars = control animals, dark gray bars = heaves-affected
horses.

Light photomicrograph of 1-2 micron sections from lung biopsy
samples taken from control (A and C) and heaves-affected (B
and D) horses in clinical remission. Figures A and B, bar = 500
microns; figures C and D, bar = 100 microns, H & E stain. a =
alveolar parenchyma, b = bronchioles, p = pleura. Figure A,
note the well-preserved alveolar parenchyma and the
compression of the parenchyma close to the staple line (arrow).

viii

74

76

78

80

82

Figure 6

The high magnification of alveolar parenchyma from a control
horse (figure C) shows individual capillaries containing
erythrocytes (arrow). The low magnification photomicrograph
from a heaves-affected horse shows peribronchial thickening.
Figure D shows peribronchial interstitial fibrosis with epithelial
hyperplasia and mucous cell metaplasia (arrows) in a heaves-
affected horse.

Light photomicrograph of 1-2 micron sections of bronchioles
from lung biopsy samples taken from a control (A) and a
heaves-affected (B) horse. Epithelium (e) and smooth muscle
(sm) are clearly visible, as are mucous accumulation in the
airway lumen (open arrow) and mild peribronchial
inflammation (dark arrow) in the heaves-affected horse. Bar =
50 microns, H & E stain.

ix

84

INTRODUCTION

Advances in surgical equipment, video technology, and the enthusiasm for
minimally invasive procedures have resulted in the emergence of refined surgical
techniques that can be accomplished with the aid of a telescope. Thoracoscopic surgery,
also known as video-assisted thoracic surgery (VATS), has been an effective procedure
for the diagnosis and treatment of many thoracic diseases. VATS, by its minimally
invasive nature, has replaced many of the traditional thoracic procedures in human
surgery. In particular, thoracoscopic pulmonary wedge resection has become a valuable
technique for lung biopsy in humans with certain pleuIOpulmonary diseases. The
surgical technique provides a quality tissue sample with high diagnostic yield and
minimal complications to the patient.

The thorax of the horse is rarely invaded for diagnostic purposes or surgical
treatment because general anesthesia and recurnbency compromise gas exchange
considerably and the addition of pneumothorax and pulmonary surgery make anesthesia a
high risk. Painful surgical incisions leading to lung dysfunction and postoperative
pleuritis present risks that are unacceptable to many clinicians. Fortunately,
thoracoscopic surgeries are now beginning to replace some of the thoracic procedures
performed in horses. Thoracoscopy has been proven to be safe in the healthy horse and
has improved our clinical understanding of disease processes in the thorax.

Respiratory diseases in horses are an important health problem and their diagnosis
can be challenging and frustrating. When less invasive diagnostic procedures fail to yield

an accurate diagnosis and prognosis, histopathological examination of the pulmonary

tissue becomes essential. Methods for lung biopsy in horses have been described;
however, the small sample size, which can preclude diagnostic interpretation, and a
number of reported complications, make these biopsy techniques undesirable in the
horse. Thoracoscopically guided lung biopsy conducted in the standing, sedated horse
may firlfill this need and become a valuable diagnostic technique for equine intrathoracic
diseases.

Equine thoracoscopy has been proven safe in the standing, sedated horse but no
study has been aimed at determining the usefulness of thoracoscopic surgery to aid in the
acquisition of pulmonary biopsy. In addition, no one has studied the cardiopulmonary
effects of thoracoscopy in horses with chronic lung disease. The purpose of the study
presented in this thesis was to evaluate the efficacy and safety of thoracoscopically
guided pulmonary wedge resection as a technique for lung biopsy in horses. The surgical
biopsy technique was studied first in healthy horses and then in horses with chronic lung
disease.

The objectives of the study were:

1. To develop a minimally invasive technique to obtain a lung sample from a horse.

2. To analyze the effects of thoracosc0pically guided pulmonary biopsy on
pulmonary gas exchange and cardiovascular function in normal horses and horses
with chronic lung disease.

3. To evaluate morbidity and complications of thoracoscopic guided pulmonary lung
biopsy in normal horses and horses with chronic lung disease.

4. To evaluate the biopsy site healing and pleural cavity after pulmonary resection.

5. To evaluate the adequacy of the acquired tissue sample for histopathological

examination.

CHAPTER 1

LITERATURE REVIEW

Thoracoscopy in humans
Historical perspective

The use of an endoscope to examine intrathoracic structures can be traced back to
the beginning of the twentieth century. In 1910, Hans C. J acobaeus, a Swedish internist,
published a report in which he described the so-called "thoracoscopy" operation. '
Jacobaeus used a cystoscope to examine the pleural space in human patients with
tuberculosis. Although thoracoscopy was primarily used for diagnostic purposes, it later
evolved into a therapeutic modality. In the early 19208, J acobaeus described the value of
severing adhesions to allow for complete lung collapse in treatment of tuberculosis.2
Thereupon, thoracoscopically guided pleural decortication became the therapeutic
regimen against tubercular pleural adhesions until the early 19508.3

In the 195 Os, the excitement about thoracoscopy lessened after the technique was
strongly criticized by a handful of opponents. J acobaeus was an internist, and thoracic
surgeons could not accept the idea that thoracoscopy had been developed in the hands of
a person who was not a surgeon. They discouraged the use of thoracoscopy for
diagnostic purposes because of its high complication rate (20%) and the limited surgical
exposure that it provided and thus favored the use of open thoracotornies.4 In addition,

the introduction of streptomycin for treatment of tuberculosis replaced the need for

surgical treatment of the disease and accelerated the decline of thoracoscopy.

While thoracoscopy fell into' disuse for years in the United States, Europeans
maintained its practice throughout the 19505 and 19605. Surgeons continued to use
thoracoscopy for treatment of tuberculosis, and began to encourage its use for evaluation
and treatment of diseases such as spontaneous pneumothorax and malignant pleural
effusions.3 During the 19705 and 19805, a few American surgeons revived the practice
of thoracoscopy to examine some pleural diseases and to obtain small lung biopsies in
patients with diffuse pneumonitis. Until the 19805, thoracoscopy was performed using
flexible endoscopes or other endoscopes (e. g., arthrosc0pes) that were designed for other
procedures.5 At that point in time, the surgical technique was limited because only one
person could see the Operative field at a given time, aspirates would often clot on the
endoscope, and the biopsy forceps were too small and difficult to manipulate.

Fortunately, in the last decade of the twentieth century, advances in video
technology allowed the therapeutic potential of thoracoscopy to flourish.6 Rigid
telescopes aided manipulation and miniaturized video cameras provided a better visual
field and enabled multiple persons to simultaneously view the procedure via a video-
monitor. This technology allowed assistants to aid the surgeon in complicated
procedures. In addition, the development of special endOSCOpic equipment enabled
surgeons to perform major surgeries with minimally invasive techniques. Accordingly,
advances in endoscopic surgical equipment, video technology, and the minimally
invasive nature of the procedure have resulted in the emergence of a new modality in
general thoracic surgery, called video-assisted thoracic surgery (VATS).

The impact of this new technology and its advantages has been so profound that,

in recent years, many thoracic surgical procedures are now performed via VATS. The

advantages of thoracoscopic procedures have been well described in various articles.“9
The procedure may be used in young children10 and the elderly. Its use in patients with
compromised cardiopulmonary or immune function (e. g., HIV-positive patients) provides
minimal risk to the patient and operating room personnel.9’ ” In humans, thoracosc0pic
surgery is the technique of choice when less invasive techniques have failed to yield a
diagnosis or resolve a problem. VATS is commonly used in the evaluation of
undiagnosed pleural and pulmonary diseases, treatment of spontaneous pneumothorax,
resection of small peripheral pulmonary lesions, lymph node and pulmonary biopsies,
treatment of empyema and resection of adhesions, window pericardectomy, and treatment
of vascular anomalies.“ ‘3 Moreover, the literature reports the use of thoracoscopic
techniques for complicated procedures such as spinal surgeries, esophageal surgeries, and

diaphragmatic hernia repair.”16

Basic concepts of thoracoscopy

Although thoracoscopic surgery can be performed under local and/or regional
anesthesia, general anesthesia and single lung ventilation is preferred in humans. Single
lung ventilation is attained by selective intubation of the primary bronchus of the non-
operated lung.l7 This allows the lung to collapse on the operative side after induction of
pneumothorax, which greatly enhances the examination of the pleural cavity and
intrathoracic organs. Contrary to laparoscopic surgery, thoracoscopic surgery rarely
requires carbon dioxide insufflation. Concerns associated with C02 insufflation, which

include hemodynamic alterations, ventilatory derangement, and embolization of C02, are

avoided. C02 insufflation may be necessary to aid in the creation of artificial
pneumothorax when single-lung ventilation cannot be achieved.17

The primary strategy of thoracoscopy or VATS is to place the instruments and the
thoracoscope so that all are oriented in the same direction, facing the target tissue. This
positioning prevents mirror imaging. The telescope must be placed at a distance from the
site of inspection or dissection. Depending on the location of the lesion, portals are placed
at a distance fiom each other to avoid restriction of vision and/or manipulation of the
instruments. Instruments for grasping and cutting are placed at the level of the target
tissue to utilize the principle of triangulation. Comparison has been made with a baseball
diamond, with the telescope at home base, the target lesion at second base, and two
instruments at first and third base.18 The use of trochar sleeves facilitates the introduction
of instruments into the thorax and allows the exchange of instruments through portals.
These basic concepts regarding portal placements are modified as necessary to
accommodate the planned procedure and the location of the lesion. At the termination of
the procedure, the thorax must be checked for bleeding and air leaks. The collapsed lung
is re-inflated by evacuation of the air through a vacuum system and negative pleural
pressure is re-established.

In approximately 20% of human patients undergoing thoracoscopic surgery,
intraoperative conversion to a standard thoracotomy is necessary for any of several
reasons, including extensive pleural adhesions, lesions that require more extensive
resection, or technical errors.18 Strategic planning is therefore essential to avoid
complications and to be prepared for thoracotomy if needed. Surgeons performing

' thoracoscopic procedures must be familiar with open approaches in case of emergency.19

Physiologic effects associated with thoracoscopy

Depending on the patient’s health status and the anesthetic protocol used during
thoracoscopy, various physiological alterations may be encountered in human patients.
Ventilation and perfusion matching in the lung and the patient's positioning are two
variables that might interact to affect the patient's homeostasis.” 21 During
thoracoscopic procedures, a pneumothorax is induced and maintained throughout the
surgery. The pneumothorax causes lung collapse in the operative hemithorax, which
greatly enhances the visual field. However, its detrimental effects might add to the
effects of lateral recumbency, sedation, or general anesthesia, thus worsening the patient's
cardiOpulmonary function.

Pneumothorax is defined as the presence of air in the pleural cavity, which occurs
as a result of lung or chest wall injury with direct or indirect trauma.21 When opening the
hemithorax, a pressure gradient is created due to the negative pressure in the pleural
space with respect to alveolar and atmospheric pressure. The negative pressure is due to
the natural tendency of the lung to collapse and the chest wall to expand. In normal
conditions, the end—expiratory pleural pressure (Ppl) is approximately —5 cm H20.
Pleural pressure becomes more negative during inspiration (Ppl = -7.5 cm H20) when the
chest wall is expanded through the effort of the inspiratory muscles. When inspiration
begins, alveolar pressure becomes slightly less than atmospheric, allowing the air to flow
inward. Therefore, alveolar and pleural pressures undergo similar changes during the
respiratory cycle, becoming more or less negative, respectively, during inspiration or
expiration.23 Transpulmonary pressure is defined as the difference in pressures between

the alveoli and pleural cavity (Ppl), and it measures the elastic forces working to collapse

the lung during expansion. The magnitude of the lung expansion while transpulrnonary
pressure increases is determined by its compliance. At fimctional residual capacity, which
defines the volume of air remaining in the lungs at the end of a passive expiratory effort,
the outward pull of the chest wall is equal to, but in opposite direction to, the inward pull
of the lung to collapse. At this time, the transmural pressure of the lung/chest system is
zero.22

When a communication between the atmosphere and the pleural space is created,
air enters the pleural cavity until the pressure gradient is eliminated or the communication
sealed. Consequently, the lung collapses to its minimal volume and the lungs'
compliance decreases. Meanwhile, the increase in pleural pressure causes a shift of the
mediastinum to the contralateral side, enlarges the ipsilateral hemithorax, and depresses
the diaphragm.24

The main physiologic consequences of pneumothorax are a decrease in the vital
capacity of the lung and a decrease in arterial Pa02. Lung collapse due to the increase in
pleural pressure causes a decrease in total lung capacity, which is the amount of air in the
lung at the end maximal inspiration, and this decreases vital capacity.”1 Patients with
pneumothorax have a reduced arterial Pa02 and increase in the alveolar-arterial oxygen
difference (A-a gradient). These physiological changes appear to be caused by low
ventilation-perfusion mismatching, intrapulrnonary shunts, and alveolar
hypoventilation.24' 25 Consequently, selective lung ventilation is necessary in humans
undergoing thoracoscopic procedures to keep adequate ventilation and optimal V/Q

ratios. General anesthesia is therefore more appropriate than local anesthesia for

thoracoscopy in humans.

Some surgeons prefer the use of local or regional anesthesia in patients
undergoing uncomplicated thoracoscopic procedures. Advantages of local techniques
over general anesthesia include the ability to have an awake, spontaneously breathing
patient, and have good analgesia. This scenario in humans mimics the situation of
thoracoscopy in the standing sedated horse. Menzies and coworkers showed that
thoracoscopy under sedation and local anesthesia was a feasible and safe procedure.26
Awake, spontaneously breathing patients in lateral decubitus position with an open chest
have impaired gas exchange as a result of paradoxical respiration and mediastinal shift.21
For this reason, it is essential to keep the procedure short and simple and supplement
oxygen as necessary.

At the end of the procedure, the lung must be re-expanded under direct vision to
re-establish the negative pressure of the pleural cavity. In humans, resolution of
pneumothorax results in dramatic improvement in hemodynamic parameters (e. g., cardiac
output, blood pressure), although abnormalities in gas exchange (decreased Pa02 and
increased A-a gradient) persist for 60 to 90 minutes after recovery and are associated with
a decrease in respiratory compliance. Norris et al. hypothesized that a relatively great
pressure is required to open a ventilatory unit that is completely closed due to the

25

collapsed lung. This observation suggests that, after re-inflation of the lung, some

areas of V/Q mismatch and intrapulrnonary shunts persist for several hours.

10

Thoracoscopic pulmonary biopsy

In the early 19705, a report by Massen described how to remove lung tissue using
thoracoscopy by pulling the tissue through the endoscope.4 The technique was helpful
for diagnosis, however, the specimen was too small and histopathology slides contained
too many artifacts, revealing the same limitations of more traditional or less invasive
techniques such as transbronchial and percutaneous lung biopsies. More recently, the
evolution of endoscopic instruments and state-of-the-art technology inspired surgeons to
perform pulmonary resections via VATS as a technique for lung biopsy. Thoracoscopic
lung biopsy is now the most commonly performed procedure in general thoracic surgical
practices.28 The primary indications for thoracoscopic lung biopsy are (1) to evaluate
solitary pulmonary nodules, (2) to evaluate an on-going process of unknown origin, and
(3) to stage malignancies in lung cancer.29 However, some clinicians discourage the use
of this procedure in patients with cancer because of the risk of dissemination of malignant
cells into the pleural cavity during or after VATS.30

Thoracoscopic or video-assisted lung biopsy is performed with the patient under
general anesthesia, using single lung ventilation, and in lateral decubitus position.” 21 As
mentioned in the previous section, triangulation is used to obtain the biopsy sample: one
portal for the telescope, a second portal for a grasper instrument, and a third portal for the
dissection or resection instrument. These thoracoscopic pulmonary resections are
accomplished with the use of biopsy forceps, endoloop ligation,31 neodymiumzyttrium

33'” or a combination thereof. Recently

aluminum garnet laser,32 endoscopic stapler,
developed innovative endoscopic stapler/cutter devices have facilitated pulmonary wedge

resection and have become the instrument of choice to perform this procedure. These

11

endoscopic staplers discharge six rows of titanium staples, with a cutting blade to divide
the tissue, thereby providing excellent hemostasis on both the pulmonary and biopsy
incision sites.

Thoracoscopy and thoracoscopic lung biopsy has proven to be an excellent
method for diagnosis and treatment of intrathoracic diseases. Reports in the literature
demonstrate the safety and utility of the procedure in thoracic diseases, in particular
interstitial lung diseasezs’ 35’ 36 Interstitial lung diseases include a variety of pulmonary
diseases with very similar clinical signs and radiographic findings. Specific pathologic
diagnosis is essential to select proper management for therapy and to predict prognosis.
Consequently, a good biopsy sample becomes important in these patients.

Thoracoscopy allows careful assessment of the lung and selective biopsy of
multiple lung segments, thereby increasing the diagnostic yield in interstitial lung
disease.36 The tissue samples are of large volume, which allows pathologist to perform
frozen section, special stains, and cultures for microorganism.” 38 Most importantly,
thoracoscopic lung biopsy, which by its very nature is limited, does not compromise
long-term morbidity or mortality to the same degree as an open thoracotomy. At least
two reports comparing open lung biopsy and biopsy via VATS has confirmed that both
techniques are equivalent in operating time, number of pathological specimens, and
diagnostic accuracy.” 36’ 39 Nonetheless, the thoracoscopic technique revealed fewer
complications after surgery and reduced time for chest tube drainage; decreased pain after
surgery; and resulted in a shorter hospital stay. Another report comparing the
histopathology evaluation of the biopsy sample did not find a difference in diagnostic

yield between techniques, although biopsy samples from the thoracoscopic technique

12

showed more artifacts.38 The authors explained that artifacts were caused by the
excessive manipulation of the tissue during video-assisted surgeries. Although this
technique has been proven safe, it does have some disadvantages when compared to the
open technique. First, the resection is limited to the periphery of the lung, thus limiting
the pulmonary resection. Secondly, open-lung biopsy techniques allow palpation and
inspection of the lung, avoiding fibrotic, non-diagnostic specimens.38
Complications reported with this VATS are rare and include pneumonia,
bleeding, postoperative pain, empyema, and air leak. The most commonly reported has
been temporary air leak from the biopsy site.40 Contraindications to thoracoscopic
procedures are the inability of the patient to tolerate general anesthesia with single-lung
ventilation, patients with densely consolidated lungs, or patients with bleeding

disorders.28 As in humans, thoracoscopically guided lung biopsy will be a useful

technique for lung biopsy in horses.

Thoracoscopy in veterinary medicine

The first report of equine thoracoscopy dates back to 1985. In this report by
Mackey and Wheat, 15 horses underwent thoracoscopy to examine their thoracic cavity.
The procedure was performed in 10 experimental horses, but later involved five clinical
cases.41 These authors described the advantages of thoracoscopy in combination with
thoracic radiographs and ultrasound examination for an accurate diagnosis and prognosis
in horses with intrathoracic diseases.41 Also in 1985, Mansmann and Strother reported

the normal thoracoscopic anatomy of the horse thorax and compared it to the thorax of

horses suffering from chronic thoracic diseases.42 The only difference between these two

13

reports was that Mackey used a 130° rigid laparoscope for surgery and Mansmann et al.
used a flexible fiberoptic endoscope. However, authors agreed that thoracosc0py, which
they called pleuroscopy, should be used as an adjunctive diagnostic tool when less
invasive diagnostic procedures fail to identify a condition.

Until recent years, thoracoscopy was only used on very rare occasions to evaluate
the thoracic cavity of horses with suspicious thoracic tumors. The technique became very
helpful for the ante-mortem diagnosis of primary thoracic tumors or metastasis and
allowed the collection of biopsy samples for accurate diagnosis. Three case reports
described the use of pleuroscopy (thoracoscopy) for diagnosis of gastroesophageal
squamous cell carcinoma, disseminated hemangiosarcoma, and cholangiocellular
carcinoma in horses.43’4‘5

In the late 19905, as a result of the vast experience with laparoscopy, surgeons
started to perform VATS in both horses and small animals. In 1998 Faunt et al.
described the cardiopulmonary effects of bilateral hemithorax ventilation and diagnostic
thoracoscopy in do gs.46 The procedure was performed under general anesthesia,
conventional mechanical ventilation, and intrapleural insufflation of N02. Dogs tolerated
the procedure well; however, significant changes were found for several cardiopulmonary
variables (decreased Pa02, increased PaCOz, increased systemic mean arterial pressure,
and decreased total peripheral vascular resistance) during bilateral lung ventilation with
sustained pneumothorax. During the same investigation, Faunt et al. evaluated lung
biopsy specimens obtained during thoracoscopy, using a commercially available ligature.

The technique allowed procurement of lung biopsy specimens from clinically normal

dogs without complications. Biopsy specimens contained sufficient structural elements

14

without artifactual distortion of pulmonary architecture to permit assessment of
pulmonary lesions.47 Also in 1998, Garcia et al. examined the thoracic cavity and
performed lung lobectomies by means of thoracoscopy in dogs.48 One year later, Jackson
et al. reported and evaluated thoracoscopic partial pericardiectomy in 13 dogs.49 Results
indicate that the procedure was technically successful in all the dogs. Another study by
Walsh et al. compared post-operative pain and morbidity of open versus thoracoscopic
partial pericardiectomy in dogs. Thoracoscopic partial pericardectomy revealed several
advantages over open partial pericardectomy including decreased postoperative pain,
fewer wound complications, and rapid return to function.50

After the results provided by these reports, surgeries that are more complicated
have been performed via thoracoscopic surgery in small animals. Video—assisted division
of the ligamentum arteriosum in dogs with persistent right aortic arch51 and thoracoscopic
epicardial radiofrequency ablation for vagal atrial fibrillation in dogs52 have been
successfully performed with minimal postoperative complications and short
hospitalization time.

In contrast to the situation in small animal surgery, thoracoscopic surgery in
horses has been used in a very limited number of cases. In 1998, Vachon and Fisher
described the use of thoracosc0py in 28 clinical cases at Chino Valley Equine Hospital,
California.53 The specific procedures performed during thoracoscopy were exploration of
the chest, biopsy of the lung and lymph node using a uterine biopsy forceps, drain
placement into pleural effusion and abscesses, transection of pleural adhesion, and
window pericardectomy. They concluded that thoracoscopic surgery is a usefiil and safe

diagnostic and therapeutic tool in horses with thoracic disease.S3 Malone et al. described

15

the surgical treatment of a diaphragmatic hernia in a horse. Thoracoscopy allowed
surgeons to determine the surgical approach to repair the hernia defect.54

Until recently, the hemodynamic effects and consequences of thoracoscopy in the
standing or anesthetized horse had not been described. In 1999, Peroni et al. evaluated
the pleuropulmonary and cardiovascular effects of thoracoscopy in six healthy horses.55
The procedure was performed under local analgesia in standing sedated horses. The
pneumothorax necessary for thoracoscopy caused slight hypoxemia and increased
pulmonary vascular resistance but was easily reversed by reinflating the lung. In
addition, detomidine administration increased total and pulmonary vascular resistance,
and decreased arterial oxygen tension. The hypoxemia caused by this alpha-2 adrenergic
agonist may exacerbate the cardiopulmonary effects caused by the operative
pneumothorax. Many parts of the thorax could be examined if the thoracoscope was
inserted at the 10th intercostal space. The only complication was a transient slight
pneumothorax in one horse in which the lung was inadvertently torn. The pneumothorax
resolved without treatment. Pleuritis never occurred and all horses made an uneventful
recovery. In addition, Peroni et al. described the normal anatomy and surgical technique
of equine thoracoscopy.56 They concluded that surgery at the 8th and 9th intercostal space
was impeded by the rigidity of the adjacent ribs, and by the presence of greater
musculature, which did not allow easy manipulation of the telescope.“5 However, if the
thoraCOSCOpe was introduced at the 10th and 11th intercostal space, excellent exploration
of the thorax was possible with no problem manipulating instruments or the telescope.

This literature review shows that thoracoscopy can be very helpful as an ancillary

tool in the diagnosis of pleuropulmonary diseases. In addition, operative thoracoscopic

l6

procedures are technically feasible and are associated with numerous advantages,
including diminished postoperative pain and morbidity. Although these procedures
require specialized equipment and surgical expertise, I anticipate that the trend toward
minimally invasive surgeries will escalate. Thoracoscopy in veterinary medicine is still
in the developmental phase but, in the next 10 years, many of the traditionally open

procedures will be performed by means of VATS.

Lung biopsy

Human patients with pulmonary infiltrates that cannot be diagnosed by routine
noninvasive methods often present a serious diagnostic problem.57 In order to institute
proper care in these patients, lung samples must be submitted for microbiological,
virological, and histopathological examination. Several techniques have been described

58. 59

for acquisition of lung biOpsy. Methods include percutaneous lung biopsy, cutting

062, transbronchial biopsy,63 thOl'aCO3‘30133'28'33 and open

needle and trephine biopsy6
biopsy.“66 Each method has its advantages and disadvantages. The decision to use one
method versus another is difficult because studies comparing various techniques are
sparse. The literature debates the relatively accuracy of various methods and how they
relate to a single clinical problem.62*S7 Burt and coworkers performed a prospective
evaluation of aspiration needle, cutting needle, transbronchial and open lung biopsy in 20
patients with pulmonary infiltrates. Open-lung biopsy was significantly better in yielding
a diagnosis than aspirate needle, cutting needle, or transbronchial biopsy.68 In addition,

the morbidity and mortality was lower when open or thoracoscopic techniques were used

to obtain samples of lung tissue.

17

In equine medicine, clinicians have used a variety of methods for lung biOpsy
when other less invasive methods failed to yield a diagnosis, and/or histological
examination was required for appropriate therapy of a patient.69 Percutaneous lung
biopsy has been reported to be the most common method used for lung biopsy in horses.
Open techniques using a small thoracotomy are rarely performed because of the high
number of complications seen in horses after thoracic surgery. Painful incisions leading
to lung dysfunction and the postoperative pleuritis provide risks that are unacceptable for
some clinicians and horse owners.

In 1970, Dungworth and Hoare described a lung biopsy technique as part of an
investigation of the effect of exposing animals to moldy hay. The technique was
performed in 22 cattle and 2 horses using a special trephine rotated by an electrical hand
drill.70 A success rate of 80% was achieved, with complications in only one cow.70
Schatzman et a1 performed the first investigation of percutaneous lung biopsy in horses in
1974.71 In that study, lung biopsy was performed in anesthetized horses using a specially
designed irephine. The authors did not report any complications in 22 horses, and good,
quality specimens were acquired for histological examination.71 Although this technique
produces a good sample tissue for histological examination, general anesthesia and lateral
recumbency is required; thus, the risk of compromised lung function and the cost of the
procedure are increased.

In 1981, Raphael and Gunson described a percutaneous lung biopsy technique
that uses a cutting needle.69 The technique described in the paper is a safe, easily
performed and inexpensive method for lung biopsy that has become the standard method

for lung biopsy in horses. The procedure is performed with the horse standing and

18

restrained in stocks. A combination of xylazine and butorphanol is used for sedation and
systemic analgesia. A 5 cm square of skin is clipped between the 7th and 9th intercostal
space, approximately 8 to 10 cm above the elbow joint.69 If a specific area of lung tissue
is to be targeted, ultrasonographic evaluation may help localize the site of interest. The
subcutaneous tissue and intercostal muscles are infiltrated with local anesthetics and a
sterile scrub is applied to the skin. A Tru Cut biopsy needle 15 cm long with a 2 cm
specimen notch (Travenol Laboratories Inc., Deerfield, Illinois, USA) or an automated
biopsy device ( Biopty, Bard Radiology Division, Covington , GA) is inserted through a
0.5 cm skin incision just cranial to the rib. The biopsy needle or device is rapidly
advanced into the lung and the biopsy sample is obtained. Lung biopsy samples are
immediately placed in formalin for fixation. If the biopsy sample is too small, multiple
samples are taken. Following biopsy, the horse is rested in a stall for 2 days.

In 1998, Savage et al. reported on a survey that was designed to obtain
information on the indications, contraindications, complications, and methodology of
percutaneous lung biopsy in horses. Investigators sent the survey to diplomates of the
American College of Internal Medicine practicing equine medicine. The results of the
study indicated that respondents were prompted to perform a lung biopsy in horses with
clinical and radiographic signs of puhnonary miliary pattern, suspicion of pulmonary
infiltrated disease, suspicion of puhnonary neoplasia, suspicion of chronic obstructive
puhnonary diseases, and suspicion of exercise induced puhnonary hemorrhage.72
Contraindications for lung biopsy reported by respondents included neonatal septicemia,

pulmonary abscessation, pleuropneumonia, and pneumonia.73

19

Two major disadvantages reported in the study73 have also been seen by others.”
71 (l) The small sample size can lead to diagnostic misinterpretation. Sometimes, it is
impossible to study the tissue due to the large number of artifacts present (e. g., artifactual
collapse and crush of alveoli). (2) Complications following percutaneous biopsy include
fatal puhnonary hemorrhage, epistaxis, collapse, pale mucous membranes, tachypnea,
respiratory distress and death. In Savage's study, 34 of the 44 respondents had seen a
complication of biopsy at least once. An estimated 356 horses underwent percutaneous
lung biopsy, and approximately 3% died after the procedure.18 These possible
complications make percutaneous biopsy of the lung an undesirable procedure for use in
horses. Therefore, there is a great need for a safe biopsy procedure in the horse.
Thoracoscopically guided lung biopsy may fulfill this need and become a valuable
diagnostic technique for equine intrathoracic disease.

Lung biopsy has been used in a few investigations to study heaves in horses.
Naylor et al., 1992 used percutaneous lung biopsy as part of his research to examine 18
horses with clinical signs of heaves.74 He evaluated the usefulness of clinical signs,
bronchoalveolar lavage, and lung biopsy as a diagnostic and prognostic aid. In 16 horses,
histological examination of the lung biopsy confirmed the diagnosis of chronic
bronchiolitis. Results suggested that biopsy of the dorsal lung lobe was more useful than
bronchalveolar lavage analysis as a diagnostic tool for the heaves-affected horses. In his
study, lung biopsy histology had a good correlation with clinical score and confirmed the
diagnosis in all the horses.74 To the contrary, Nyrnan and coworkers did not find a
correlation between clinical scores, V/Q relationships, and pathology of lung samples

5

obtained by percutaneous lung biopsy.7 Authors did find significant agreement between

20

the extent of bronchial epithelial hyperplasia in necropsy specimen of lungs and the
degree of abnormal ventilation/perfusion mismatching. Authors commented that in
biopsy samples obtained by percutaneous techniques, small airways included in the
biopsies were too small to provide useful information.75

In summary, percutaneous lung biopsy is used to obtain pulmonary tissue suitable
for histological examination. Histological evaluation and culture of percutaneous lung
biopsy samples have been used to supply diagnostic information in horses with lung
disease.” 77 Unfortunately, the small sample size can preclude diagnostic interpretation.

69, 71

Lung biopsies are not without risk; a number of complications may occur, including

fatal puhnonary hemorrhage.

Heaves
Introduction

Recurrent airway obstruction, commonly called heaves, is considered the major
cause of respiratory tract disease in horses.78 Heaves is an inflammatory process of the
lower airways causing reversible airway obstruction in susceptible horses. It is a disease
of stabled horses and the prevalence is reported to be highest in the Northern
Hemisphere. After exposure to hay and dust during stabling, heaves-susceptible horses
develop episodes of airway obstruction. Disease remission occurs when the horse’s
environment is changed (pasture turnout). During an episode of heaves, horses develop
respiratory distress, cough, mucopurulent nasal discharge, and exercise intolerance.

Summer pasture-associated obstructive pulmonary disease (SPAOPD) is another seasonal

21

form of the disease observed in horses pastured in the southern region of the United
States during late spring, summer, and early autumn.79

In this literature review, the etiology, clinical signs, pathology, pathophysiology,
diagnosis, and treatment of heaves in horses are described. The pathological

characteristics of heaves are emphasized in this review.

Etiology

Recent studies suggest that heaves is caused by an allergic response to inhaled
spores coming from moldy hay and bedding.80 The specific allergic mechanisms are still
unclear, but type 1 (anaphylactic), type 3 (immune complex), and type 4 (delayed
hypersensitivity) allergic responses have been implicated. Exposure of heaves-
susceptible horses to poor-quality, dusty-moldy hay causes airway inflammation that is
accompanied by acute airway obstruction. Present evidences suggest that dust particles
from moldy hay contain a variety of potential allergens. Potential allergens causing
heaves-like syndrome in horses include Aspergillusfumigatus, F aenia rectivirgula, and
Thermoactynomices vulgarz's.81'83 These allergen spores are small enough that they can
be inhaled and deposited in the smaller airways (bronchioles), inducing airway
inflammation. Natural challenges (stabling and feeding poor-quality hay) can repeatedly
induce airway obstruction in heaves-affected animals.”85

In 1993, McGorum et al. compared the effects of natural exposure to hay and
bedding to challenge with potential allergens (Aspergillusfumigatus, Faenia rectivz’rgula,

and Ihermoactynomices vulgaris) in healthy horses and heaves-susceptible horses.

Within 1.5 hours, natural exposure induced lung dysfunction in heaves-susceptible horses

22

but not in control horses.83 Five hours following exposure, hypoxemia occurred and the
number of neutrophils in the BALF of heaves-affected horses increased. Exposure of
potential allergens to heaves-susceptible horses caused a less severe neutrophilia in the
BALF and was unaccompanied by lung dysfirnction. In this study, control horses never
developed pulmonary dysfirnction following the natural or inhalation challenges. Authors
concluded that heaves is a hypersensitivity response to specific antigens rather than a
non-specific response to dust and irritants in stable environment.83 In a review article by
Robinson et al., the authors suggested that duration of exposure, a combination of
antigens, and/or other factors might be important in the pathogenesis of heaves.86
The immune basis of heaves is supported by studies of pulmonary lymphocytes
population and immunoglobulin levels in respiratory tract secretions from affected
animals.” 88 Investigators have studied allergic skin testing and serum precipitin to
explain the immune mechanism and have identified antigens involved in heaves. Results
from these studies are inconclusive and reflect exposure to the antigens rather than
susceptibility to the disease. A recent study by Lavoie et a1. reveals that inflammatory
cells in lungs from horses with heaves display a predominant Th2-type cytokine profile
that is consistent with the hypothesis that heaves is an allergic condition with similarity to
human asthma.89 The exact mechanism is not clear, but T-lymphocyte cytokines may
play a central role in the selective recruitment of neutrophils into the airways in
susceptible horses. Further studies are required to understand the relationship between T-
lymphocyte cytokines and airway neutrophilia.
9o

Preceding viral infection has also been suggested to cause heaves in horses.

Viral infections cause damage to the mucocilliary clereance mechanism, causing

23

increased retention of particulate antigens and an altered immune responses induced by
the virus.80 However, there is presently no evidence to support this theory. In 1998,
McGorum and coworkers studied the effects of inhaled endotoxins in control and heaves-
affected horses. Authors concluded that inhaled endotoxins contributed to airway
inflammation in both heaves and control horses when they were exposed to high levels of
endotoxins in poor stable environments.” Indeed, it is now believed that endotoxins

might play an important role in the pathogenesis of heaves.

Clinical signs

Clinical signs of heaves vary between individuals and vary with the severity of
the disease. Horses with mild disease only show cough and nasal discharge during
exercise, or mild exercise intolerance.80 Chronic coughing, nasal discharge, increased
respiratory effort, and obvious exercise intolerance characterize severe cases.
Furthermore, severe cases of the condition frequently demonstrate clinical signs at rest,
which include chronic cough and increased expiratory effort. After long-standing disease,
these horses develop a distinctive pattern of breathing. This breathing pattern is
characterized by a biphasic expiratory effort with the thoracic component of expiration
followed by an abdominal component. Repeated expiratory effort causes hypertrophy of
the abdominal musculature (external abdominal oblique muscle) and the development of

the clinically recognized “heave line.”

24

Pathophysiology

After exposure to the inciting cause, acute inflammation develops in the airway of
heaves-affected horses and is accompanied by episodes of diffuse airway obstruction.
The diffirse airway obstruction is primarily a result of bronchospasm, mucus

1.86 During clinical disease,

accumulation, and inflammatory reaction in the airway wal
horses affected by heaves have an increased airway resistance and lower dynamic
compliance.80 Diffuse airway obstruction results in uneven distribution of ventilation that
can be detected by a prolongation of nitrogen washout.92 Severe abnormalities in
ventilation/perfusion ratios then result in hypoxemia.75

While in clinical remission, tidal volume, respiratory rate, and minute ventilation
of heaves-susceptible horses do not significantly differ from those of control animals.
However, during a heaves episode, minute ventilation increases due to increase in
respiratory rate but tidal volume remains unchanged.75 In horses with severe, long-

standing disease, puhnonary hypertension may occur secondary to hypoxic

vasoconstriction of pulmonary arteries.75

Pathogenesis

Exposure of heave-susceptible horses to poor quality, dusty hay and bedding
induces inflammation in the lower airway. Three to five hours after natural challenge,
neutrophils are attracted and accumulated in the lungs. Neutrophils are attracted by non-
specific and specific mechanisms. Non-specific mechanisms of neutrophil chemostasis
involve direct chemotactic activity of plant particles, activation of the alternate

complement pathway, and secretion of chemotactic cytokines by alveolar macrophages.

25

These non-specific mechanisms might account for the mild neutrophilia seen on BALF in
normal horses and ponies after exposure to dusty environment.” Robinson proposed that
inhalation of antigens by heaves horses initiates a specific immune response in which
alveolar macrophages and lymphocytes produce cytokines that recruit neutrophils into the
lung.86 The neutrOphilic response in horses varies between animals, however, reports
revealed that the percentage of neutrophils in BALF increases with the severity of the
disease.93

Inflammatory mediators play a role in the pathogenesis of heaves. Nonetheless,
the importance of each family of mediators is uncertain. One study has shown that
activation of the arachidonic acid cascades occur during an episode of heaves in affected
animals.” The inflammatory response is accompanied by increased levels of histamine
in BALF, increased plasma levels of thromboxane and lS-hydroxyeicosatetraenoic acid
(lS-HETE), and a decrease in the production of prostaglandin E2 (inhibitory prostanoid
that inhibit smooth muscle contraction) by the airway mucosa. Furthermore, a study by
Man et al. showed that leukotrines LTD4 induced a dose-dependent airway obstruction.96
The importance of these leukotrines in heaves is unclear. A recent study shows evidence
of a predominant Th2- type cytokine profile in heaves horses that is similar to the allergic
response seen in humans with atopic asthma.89 These results are consistent with the
hypothesis that heaves is an allergic condition with similarities to human asthma.

Certain mediators also initiate a parasympathetically mediated bronchospasm.
Bronchospasm is caused by direct activation of muscarinic receptors by acetylcholine and
by indirect effects exerted via the autonomic system. In 1993, Robinson and coworkers

showed that the administration of anticholinergic drugs to affected horses caused

26

bronchodilation that relieved the diffuse airway obstruction.97 Furthermore, activation of
airway reflexes, loss of inhibitory mechanisms (non-adrenergic non-cholinergic
inhibitory innervation), and decrease in PGE2 inhibition are also factors contributing to
airway obstruction.

Non-specific airway hyperresponsiviness (narrowing of the airway in response to
a variety of antigenic and non-specific stimuli) is another factor contributing to airway
obstruction. Heaves-susceptible horses exposed to natural challenges exhibit airway
hyperresponsiviness.84 When the same horses return to the pasture, airway
hyperresponsiviness decreases so that heaves-affected horses did not show any difference
in airway hyperresponsiviness from controls.84 The mechanism of airway.
hyperresponsiviness and its role in heaves is still uncertain, and further research is

required in this area to clarify its precise role in disease.

Pathology
The most extensive lesion in heaves is chronic bronchiolitis with obstruction of
airways in the lower respiratory tract. The pathology varies from case to case and with
the severity of the disease. Furthermore, the morphological and ultrastructural alterations
are not uniform and are variable between different regions of the lung.97’ 98 On gross
examination, the lungs of heaves-affected horses appear hyperinflated and fail to collapse
when the chest is open. Failure to collapse is a result of gas trapping in the alveoli due to
obstruction in the bronchioles and is not due to a true emphysema.86

The predominant histopathological findings in heaves involve the accumulation of

mucus and inflammatory cells in the lumen of smaller airways, goblet cell metaplasia,

27

and peribronchial inflammatory infiltration. In 1990, Kaup et al. performed extensive
light and electron microscope studies of the lung in 28 horses suffering from recurrent
airway obstruction. Ultrastructural alterations of the larger conducting airways only
occurred in the bronchial epithelium.97 Electron microscopy evaluation of larger airways
showed a marked hyperplasia of bronchial epithelium that was accompanied by loss of
ciliated cells. Numerous ciliary malformations were also found in these horses. Kaup and
coworkers considered these alterations in the larger airways insignificant. These authors
considered the smaller airways to bethe major site of the pathological process of heaves.

In the small airways, peribronchial accumulation of inflammatory cells, mainly
lymphocytes and plasma cells, isusually present in long-standing cases.98 The interstitial
lyrnphocytic infiltration can be regarded as a manifestation of the chronic course. Plugs
of mucus, intralurninal accumulation of neutrophils, and pathological changes of the
bronchial epithelium narrow the bronchial lumen. Depending on the severity of the
disease, bronchial wall changes consist of increased cellular desquarnation, epithelial
necrosis, epithelial hyperplasia, and non-purulent peribronchial inflammatory

98 Kaup et al. noticed that Clara cells suffered major structural injuries that

infiltration.
consist of loss of cell granules, increase in endoplasmic reticulum, and degenerative
changes to the cytoplasm. Consequently, dysfimctional Clara cells, which lack cell
differentiation, were then replaced by goblet cells.

In the alveoli, light microscopy shows alveolar hyperinflation, necrosis of type I
pneumocytes and replacement by type II pneumocytes, and alveolar fibrosis.98 Scanning

electron microscopy of the alveoli reveals marked alveolar dilation and a pronounced

increase in Kohn’s pores. Increase in the number of Kohn’s pores provides collateral

28

ventilation to neighboring alveoli to equilibrate the air trapping due to the airway
obstruction. Kaup et al. also found that some horses showed morphological signs of
interference with the production of surfactants in the form of marked cysts with lamellar
structures in type II pneumocytes.

Subjective evaluations of small airway walls in heaves-affected horses suggest an
increase in the airway wall thickness per millimeter of basement membrane.
Inflammatory infiltrates, smooth muscle hypertrophy, and hyperplasia of epithelium and
secretory glands cause the increase in thickness. Further research in airway morphometry
is necessary to quantify these changes. In addition, fibrosis of the bronchial wall and
neighboring alveoli occurs in very severe cases. The fibrosis is generally regarded as a
reparative mechanism of the airway in cases of chronic destructive diseases.
Unfortunately, alveolar fibrosis is an irreversible alteration to the lung.

Reports in the literature demonstrate that findings from histological examination
of lung tissue taken by biopsy or from necropsy specimens have a good correlation with
clinical signs.” 75’ 77 Used together, the degree of bronchiolar neutrOphilic infiltration
and goblet cell metaplasia had the highest correlation with clinical signs.74 This suggests
that these changes are important in the pathogenesis of the disease. In these studies,
biopsy specimens were always reliable for diagnosis of heaves. In addition, Nyman and
co-investigators studied the ventilation/perfusion relationship and related the information
on puhnonary gas exchange to clinical signs and lung pathology in horses affected with
heaves. Investigators found a significant correlation between the extent of bronchiolar
epithelial hyperplasia in necropsy specimens and the degree of ventilation of high V/Q

regions and dead space in the lung. They concluded that hyperinflation of the lung due to

29

obstructed airways was the common denominator of increased ventilation of high V/Q

regions and dead space in horses with heaves.7S

Diagnosis

A presumptive diagnosis of heaves is usually made based on medical history,
clinical signs, and response to therapy. Several diagnostic tests, including cytological
evaluation of bronchoalveolar fluid (BALF) and lung function tests, are used to confirm
the diagnosis.

Cytological examination of BALF correlates well with histological lesions of
horses affected with heaves.74 After exposure to dusty hay, the cytological distribution of
BALF in heave horses consists of predominantly non-degenerative neutrophils.
However, cytological characteristics of BALF are quite variable and airway inflammation
can be seen without airway obstruction. Therefore, BALF alone does not enable
clinicians to differentiate between heaves-affected horses and horses with airway
inflammation due to other causes.

Arterial blood gas analysis and measurement of intrapleural pressure are the
pulmonary function tests that help quantify the degree of puhnonary dysfunction in
horses with heaves. Although insensitive, these diagnostic tests help to confirm a
diagnosis. Horses showing clinical signs of heaves commonly have a maximum change
in pleural pressure during tidal breathing greater than 6 mm Hg.80 In addition, arterial
oxygen tension is generally lower than 82 mmHg.80 Studies have shown that clinical
score and maximum change of intrathoracic pressure during tidal volume (A Ppl), are

moderately accurate for establishing a diagnosis. Measurement of pulmonary resistance

30

and dynamic compliance, tidal breathing flow-volume loops, and forced expiration test
are accurate tests and can help to detect earlier stages of disease. However, special
equipment and training is required to perform these tests. These diagnostic tools are not
practical for clinical situations but are often used in research.

Lung biopsy has been advocated as another diagnostic method.” 79
Histopathological examinations of biopsy samples from heaves-affected horses have
shown a high correlation with severity of the disease and clinical score-'4' 79 Examination
of lung biopsy histology from heaves-affected horses reveals pathological changes
characteristics of the disease that are useful confirming the presence of heaves in most of
the cases. Although the biopsy is a helpful diagnostic aid, severity of pathological
changes seen in lung biopsy alone is not a good prognosticator for life expectancy in
heaves-affected horses. Response to therapy seems to be a better prognosticator than
clinical and laboratory findings.79 Lung biopsies are rarely needed for diagnosis of heaves
because of the availability of less invasive diagnostics tools, but sometimes
histopathological examination of lung samples provides good information.

Because heaves is a diffuse disease but pathological changes in the lung vary and
are not uniform, an isolated lung biopsy may not be completely representative of overall
pathological status. Obtaining multiple samples from both sides of the lung or obtaining
a larger biopsy sample, by thoracoscopically guided lung biopsy, might increase the

reliability of lung biopsies.

31

Treatment

The therapy for heaves depends on the severity of the condition. For unknown
reasons, severely affected horses do not respond well to therapy. Irreversible airway
injury (alveolar fibrosis) and severe airway hyperresponsiviness may contribute to this
phenomenon. The major goal for treatment is to relieve the airway obstruction, to

reduce airway inflammation, and to remove the animal from the source of exposure.99

Environmental control

Environmental control is the most important component of therapy and involves
the maintenance of allergens and airborne pollutants below the threshold limiting value
that will induce disease in the susceptible animal. The ideal way to treat heaves is to
maintain the horse in the pasture with no access to hay or straw. When pasture turn out is
not possible, bedding the stall with something other than straw becomes essential.
Although difficult, elimination of contact with hay appears to be the most important
aspect of environmental control.100 Feeding grass silage and complete pelleted diets are
very effective.101 In very mild cases, feeding soaked hay may be enough to reduce the
exposure of the horse to allergens. Environmental changes can relieve airway obstruction

within three to seven days in heaves-affected horses.102

Relieve airway obstruction
Bronchospasm is the primary basis of airway obstruction in heaves. Three types

of bronchodilators are used in the treatment of heaves. Bronchodilator drugs include

anticholinergics (e. g., atropine), sympathomimetics (Ii-adrenergic agonists — e. g.,

32

clenbuterol, albuterol, terbutaline), and phosphodiesterase inhibitors (e.g.,
aminOphylline).80 These bronchodilators have different mechanisms of action and side
effects. Therefore, familiarity with the specific drug is essential before usage. In humans,
bronchodilator agents delivered by aerosol are more effective than oral administration
because higher concentrations of the drug reach the smaller airway with less systemic
side effects. Fortunately, specially designed masks (i.e., Aeromask ES) and aerosol
delivery systems (Torpex) are now available for horses.103 ’ 104 The effectiveness of

inhalation therapy in horses has been described in the literature.105

Relieve airway inflammation
Corticosteroids are the most effective anti-inflammatory agents that reduce airway
inflammation in heaves-affected horses. Nonetheless, inflammation will recur if the
steroid administration is discontinued unless exposure to potential allergens is reduced.
The deveIOpment of laminitis or Cushing-like syndromes in steroid treated horses is
always a concern but is over-emphasized. Consequently, the lowest effective dose to
maintain clinical remission is used to reduce potential side effects.99
Dexamethasone is the steroid of choice for treatment of heaves.106 Both oral and
injectable dexarnethasone preparations are proven to be effective in reducing airway
inflammation in horses. The traditional use of prednisone tablets for the treatment of
heaves is now abandoned. Recent investigations have shown that administration of
predinisone orally is ineffective in the treatment of heaves.m7

Inhaled corticosteroid therapy delivered by a hand-held metered dose delivery

device (3M Animal Care products, St. Paul, Minn.) has recently been shown to improve

33

pulmonary function in horses with heaves. In 1998, Rush et al. studied the effects of
beclomethasone delivered by aerosol in horses with heaves. In this study, the
investigator found significant improvement in pulmonary function in heaves-affected

horses treated with the inhaled steroids.108

Reasons for using heaves-aflected horses in this research

Throughout the years, numerous studies have answered many questions regarding
heaves in horses but, from this review, we can appreciate that there are still many
unsolved questions. In particular, there is a poor understanding of the relationship
between the pathogenesis and pathology of the disease. Recent studies have made it clear
that several inflammatory mediators are important in the pathogenesis of heaves but their
exact role is uncertain. Researchers have to assess these mediators at the cellular level by
evaluating their effects on pulmonary tissues. Pulmonary biopsy can provide us tissue
samples that can be utilized to observe and measure inflammatory and airway remodeling
changes using electron microscopy, immuno-histochemistry, and in situ hybridization.
The trafficking of cytokines and responsiveness to induced antigens and treatment
modalities (e. g., steroids and bronchodilators) can be evaluated by direct methods using a
biopsy specimen.

Because inflammatory mediators and therapeutic drugs work at different sites and
times, scientists must evaluate the cellular changes by examining multiple tissue samples
at different time intervals. Unfortunately, biopsy techniques described for horses are not
extremely safe and do not provide quality tissue samples that can be useful for pulmonary

research. Accordingly, there is a great need for a safe biopsy procedure that would allow

34

tissues to be taken repeatedly from the same horse during exposure to an antigen or
during a treatment regimen. Therefore, thoracoscopically guided pulmonary biopsy may
fulfill this need and become a usefiil tool for pulmonary research.

Thoracoscopy in clinical situations is meant to be utilized in horses with
pleuropulmonary diseases and the safety of the procedure in these horses needs to be
addressed before its clinical use. The use of heaves-affected horses in the study
presented in this thesis allowed us to evaluate the safety and physiological effects
associated with thoracoscopy in horses with chronic lung disease. I hypothesized that the

procedure is safe in these horses.

Summary

This literature review describes the indications, principles, and complications of
thoracoscopy and thoracoscopically guided lung biopsy. The clinical application of
thoracoscopy in horses has been proven, but the safety and efficiency of VATS to aid in
the acquisition of a puhnonary biopsy has not been studied. Evaluation of the technique
requires investigation of the pathophysiological consequences and safety of the procedure
during the surgery. In addition, the biopsy tissue sample obtained via this method must
be evaluated for adequate representation of the lung tissue. In order to investigate the
physiological effects of thoracoscopic pulmonary biopsy in horses and relate it to clinical
cases, normal horses and horses affected with heaves were selected for the study.

The experiment was designed to evaluate the safety of thoracoscopic-guided lung
biopsy during surgery and in the two weeks after surgery. The purpose of the study

described in this thesis was to evaluate the efficiency and safety of thoracoscopically

35

guided pulmonary wedge resection as a technique for lung biopsy in the standing, sedated

horse.

36

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37

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11.

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13.

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Dieter RS. The history of thoracoscopy. In Thoracoscopy for surgeons: Diagnostic
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45

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59: 1039-1043.

46

CHAPTER 2
THORACOSCOPIC PULMONARY BIOPSY: TECHNIQUE AND SAFETY IN

HORSES

Summary

Ob jective—To evaluate the safety of thoracoscopically guided lung biopsy in horses.
Animals—Ten horses (5 control, 5 affected with recurrent airway obstruction [heaves]).
Procedure—Horses underwent two thoracoscopic procedures. During the first procedure,
each horse had a thoracoscopic lung biopsy. At assigned intervals before, during, and
after the surgery, the following variables were measured: heart rate, respiratory rate,
arterial pH, Pa02, PaCOz, and systemic and puhnonary arterial pressures. Physical
examination, CBC, thoracic radiography, and ultrasound were performed 24 hours before
and 2 and 48 hours after surgery. Biopsy specimens were assessed subjectively by
histological examination. All horses underwent a second thoracoscopy 14 days later to
evaluate the biOpsy site.

Results—The technique provided an excellent approach for obtaining biopsy specimens
adequate for histological evaluation in all the horses. Heart rate and respiratory rate
decreased significantly following detomidine administration. The procedure had no
significant effect on arterial pH, PaCOz, or mean arterial and pulmonary arterial
pressures. A significant transient decrease in Pa02 was detected after pulmonary biopsy.
All horses except one were clinically normal after thoracoscopic surgery. One horse

developed hemothorax due to iatrogenic injury to the diaphragm with a trochar. The

47

second thoracosc0py revealed minimal inflammation and no adhesions in the thoracic
cavity.

Conclusion and Clinical Relevance—Thoracoscopic lung biopsy is well tolerated, and
provides a minimally invasive method to obtain lung specimens from both diseased and
healthy horses. This new technique may be applicable for the diagnosis of diseases

involving the lung and thorax in horses.

Introduction

Thoracoscopic surgery, also know as video-assisted thoracic surgery (VATS), has
been applied in human medicine in the past decade to virtually every disease process
encountered in the thorax.1 Advances in endoscopy and laparoscopic surgical equipment
and the enthusiasm for minimally invasive procedures have resulted in the emergence of
refined surgical techniques that can be accomplished with the aid of the thoracoscope.
Lately, VATS has replaced many of the open thoracic surgical techniques because of its
efficacy and safety. Recent studies have shown that, in humans, post-operative pain is
markedly reduced, intensive medical services are minimized, hospitalization is shortened,
and recovery time is decreased, compared to patients in whom the traditional

(1.2'4 In addition, thoracoscopy now serves as a useful

thoracotomy was perfonne
modality for diagnosis of thoracic disease.

Veterinary practitioners report that respiratory diseases are second only to colic in
importance as a health problem of horses, but their diagnosis can be challenging and

fi'ustrating. 5 Modalities for diagnosis in equine thoracic diseases include thoracic

auscultation and percussion, radiography, ultrasonography, and analysis of tracheal

48

aspirates, bronchoalveolar lavage fluid, and/or pleural fluid. Despite these diagnostic
tools, accurate diagnosis and prognosis of certain pleuropulmonary diseases often
requires histopathological evaluation of the pulmonary tissue. Equine internists have used
transbronchial6 and especially percutaneous7’ 8 methods to obtain a lung biopsy from
horses. Savage et al. surveyed diplomates of the American College of Veterinary Internal
Medicine about percutaneous lung biopsy in horses. 9 Two major disadvantages were
reported: 1) the small sample size can lead to diagnostic misinterpretation, and 2) there
are a number of complications, including epistaxis, tachypnea, and respiratory distress.
In addition, the report also described other complications such as fatal puhnonary
hemorrhage and sudden collapse after the procedure. These possible complications make
percutaneous biopsy of the lung an undesirableprocedure for use in horses and there is a
great need for a safe biOpsy procedure. Thoracoscopically guided lung biopsy conducted
in the standing sedated horse may fulfill this need and become a valuable diagnostic and
therapeutic technique for horses.

Thoracoscopy has been used for diagnosis and surgery in horses on a very limited
basis. In three case reports, pleuroscopy was used for diagnosis of thoracic neoplasia in
horses. [0'12 Vachon and Fischer described the use of thoracoscopy for exploration of the
chest, biopsy of the lung and lymph node using uterine biopsy forceps, drain placement
into pleural effusion and abscesses, transection of pleural adhesions, and window
pericardectomy. They concluded that thoracoscopic surgery could be a useful diagnostic
and therapeutic tool in horses with thoracic disease but that there is a need for further
evaluation of this technique. 13 Recently, Peroni et al. demonstrated that thoracoscopy

performed in healthy horses under sedation did not have any detrimental effect on

49

cardiopulmonary fimction and did not cause any post-operative complications during or
after the surgery. 14

Because the thorax can be safely invaded and examined in the sedated standing
horse, a study was designed to determine the safety of lung biopsy conducted under
similar conditions. The purpose of the study was to evaluate the efficacy and safety of
thoracoscopically guided pulmonary wedge resection as a technique for lung biopsy in
horses. The objectives of this study were to evaluate the ability to obtain the desired
biopsy using a commercially available endoscopic cutter/stapler, to evaluate the
cardiopulmonary function of horses during surgery, to evaluate the morbidity and
complications during and after the surgery, and to evaluate the quality of the tissue
sample that was obtained. We began with healthy horses and then studied the use of the

technique in horses with chronic lung disease.

Materials and Methods

Horses

Ten adult horses (8 geldings and 2 mares, age 3 to 20 years, weight 420 to 510
kg) were used in the study. Five horses served as controls and five were affected with
recurrent airway obstruction (heaves). To be designated as controls, animals had to have
no history of respiratory disease; no abnormal respiratory sounds on auscultation; no
evidence of pleuritis, pneumonia, pneumothorax, or neoplasia on thoracic radiographs;
and normal arterial oxygen tension (Pa02 > 85 mmHg). Bronchoalveolar lavage fluid

(BALF) had to have less than 10% neutrophils in the cytology distribution. Heaves-

50

affected horses were from the Michigan State University Pulmonary Laboratory research
herd. These horses had a history of environmentally induced measurable airway
obstruction that was partially reversible after atropine administration. In addition,
exposure to hay dust resulted in an increased number of neutrophils in bronchoalveolar
lavage fluid. ‘5 Lung biopsy of the heaves-affected horses was conducted when they
were in clinical remission without signs of respiratory distress. All of the horses in the
study underwent two thoracoscopic surgeries. In the first surgery, a thoracoscopically
guided lung biopsy was performed. Fourteen days after the first surgery, a second
thoracosc0py was performed to evaluate the pleural cavity and pulmonary biopsy site.
The All-University Committee on Animal Use and Care of Michigan State University

approved this survival study.

Cardiopulmonary function

A 14 gauge, 13.3 cm (5.25 inches) intravenous catheteral was placed in the right
jugular vein for drugs and fluid administration. To measure pulmonary arterial pressures,
a balloon-tipped, 7 French, 110 cm (44 inches) Swan-Ganz catheter was placed through
the left jugular vein until the catheter floated into the puhnonary artery outflow tract.
Location of the catheter in the pulmonary arterial outflow tract was confirmed by the
shape of the pressure wave as recorded by the pressure transducer and observed on the
monitor. Mean arterial blood pressure was monitored during the procedure by
introducing an intra-arterial catheterb (20 gauge, 2.5 cm, [1- inch] catheter) in the

transverse facial artery. The catheters were then connected to the pressure transducer.

51

The same intra-arterial catheter was used to obtain arterial blood samples for blood gas
analysis.

The intra-arterial and the Swan-Ganz catheters were connected to a physiological
data collection systemc to simultaneously measure systemic and pulmonary arterial
pressures. Pressure transducers were calibrated against a mercury manometer and placed
at the level of the point of the shoulder that is level with the right atrium. The pressure
transducers were connected to a computer that allowed the on-screen monitoring and
storage of data.

During each measurement period, systemic and pulmonary arterial pressure data
were recorded for 2 minutes. Mean systemic arterial and mean pulmonary arterial
pressures were calculated by the equation: mean MAP or PAP= mean diastolic pressure +
[(mean systolic-mean diastolic pressure) / 3]. Other variables measured during each
interval were heart rate and respiration rate.

At each measurement period, 2 to 3 ml of arterial blood were drawn in
heparinized syringes and were immediately sealed and maintained in ice until analyzed
(within one hour of collection). Arterial blood gas analyses were performed using a Stat
Profile Plus 9 blood gas and electrolyte analyzerd. Blood gas analyses included arterial
pH, Pa02, PaCOz, and 802%. Blood gas partial pressures were measured at 37°C and

values were corrected to the rectal temperature of the horse.
Experimental design

Twenty-four hours before surgery, all the animals in the study had a series of

procedures to evaluate their health status, in particular their respiratory system.

52

Diagnostic procedures included physical examination, a complete blood count and
fibrinogen, measurement of arterial blood gases, thoracic radiographs, thoracic
ultrasound, and bronchoalveolar lavage. Physical examination included measurement of
heart and respiratory rate and rectal temperature, thoracic auscultation, and assessment of
mucous membrane color and capillary refill time. Bronchoalveolar lavage technique and
BALF analysis were performed as previously described. 14

During the surgical procedure, the following variables were monitored and
recorded: arterial blood gases (arterial pH, Pa02, PaCOz), systemic arterial pressure,
pulmonary arterial pressure, hematocrit (PCV) and total protein (TP), heart rate
(beats/min), and respiratory rate (breaths/min). Data were recorded at six intervals: before
sedation (baseline), after administration of detomidine HCl and butorphanol tartrate
(sedation), immediately after induction of the pneumothorax, one minute before
puhnonary wedge resection (pre-biopsy), one minute after pulmonary wedge resection
(post-biospy), and immediately after reinflation of the lung and removal of the
thoracoscope. After surgery, all the horses were hospitalized for 48 hours at the Large
Animal Clinic for follow-up evaluation and observation.

Two hours after surgery, horses received complete physical examinations, arterial
blood gas analysis thoracic radiographs, and ultrasound examination to evaluate the
animals for possible complications such as pneumothorax and hemothorax. After surgery,
the horses were monitored every 2 hours for behavioral signs of pain or discomfort
(agitation, pawing, and signs of colic), epistaxis, and/or respiratory distress. For the first
24 hours, horses received physical examinations every 6 hours. In addition, PCV and TS

were measured every 6 hours for 48 hours. The same follow-up protocol was performed

53

48 hours after surgery, including measurement of blood gases, complete blood counts,
and a chemistry profile.

All of the horses underwent a second thoracoscopy 14 days after the lung biopsy
procedure. The second surgery was necessary to evaluate the biopsy site and the pleural
cavity for signs of pleural lesions and intrathoracic adhesions. To evaluate health status
before surgery, a physical examination was performed, and blood samples were
submitted for measurement of CBC, fibrinogen, and chemistry profiles. The horses had
the same surgical and anesthesia protocol as for the first surgery but with no pulmonary

biopsy.

Surgical procedure

The instruments used for thoracoscopy were 30°, 10 mm x 58 cm rigid
laparoscope“, videocamera°, light cable, and a 250-watt xenon light sourcef. All of the
procedures were observed on a video monitor and recorded on a digital videocarnerag.
Endoscopic forcepsh (10 mm atraumatic Babcock forceps) were used to manipulate the
lung. An endoscopic staplerh (EZ 45 endoscopic linear cutter, 45 mm) was used to
perform the lung biOpsy.

Two hours before surgery and for 24 hours thereafter, systemic antibiotics
(arnpicillin trihydratei 10 mg/kg IV q 8 h and gentomicin sulfatei 6.6 mg/kg IV q 24 h)
were administered to each horse for infection prophylaxis. In addition, the non-steroidal
anti-inflammatory drug flunixin megluminek (1.1 mg/kg IV q 12 h) was given for the
same period. The surgical procedure was performed with the animal restrained in stocks

and sedated by means of a continuous IV drip infusion of detomidine HCl1 (6 rig/kg

54

loading dose followed by 0.8 ug/kg/min to effect). At the time of surgery, analgesia was
provided by a single bolus of butorphanol tartratem (0.04 mg/kg IV) and local infusion of
20 to 30 ml of 2% carbocaine" into the subcutaneous tissue and intercostal musculature at
each surgery site.

The right thoracic chest wall was clipped and aseptically prepared for surgery. A
1-cm stab incision was made through skin and muscles at the 13th intercostal space
approximately 5 cm ventral to the epaxial muscles. In order to prevent damage to the
lung by the trochar through which the thoracoscope was inserted, a pneumothorax was
induced by inserting a teat cannula into the thoracic cavity through the incision and
intercostal muscles. The first trochar/cannulah (dilating tip 10/ 12 mm) system for the
telesc0pe was placed. Once the telesc0pe was inserted, the thorax was explored and a
site for lung biopsy was chosen. A biopsy specimen of the caudal aspect of the left
caudal lung lobe was targeted. To achieve triangulation, two additional instrument portals
were made at least 2-3 intercostal spaces apart to avoid obstruction of vision or restriction
of manipulations of instruments (Fig l). Thoracoscopic viewing of the surgical field
prevented injuries to thoracic structures during insertion of the two instrument trochars.
Instrument portals were placed as follows: one trochar was placed one or two intercostal
spaces cranial to and about 15 cm ventral to the first trochar; and the other instrument
portal was placed at intercostal space 15 about 10 cm ventral to the first trochar. The
tissue to be removed was grasped with atraumatic forceps and, using endoscopic
staplers,h the biopsy sample was obtained (Fig 2). On each discharge, this special
endoscopic stapler inserted and closed two staggered rows of titanium staples, while it

simultaneously separated the biOpsy sample from the lung. The endosc0pic staple

55

cartridge we used was 45 mm in total length with a staple size of 4.1 mm. When
necessary, the lung clamp and staple device were interchanged between portals to
facilitate the approach to the tissue specimen. Because the biopsy sample was too large to
be withdrawn through the cannula, the latter was withdrawn and, at the same time, the
sample was gently retrieved through the incision. The biopsy site and thoracic cavity
were inspected one final time for hemorrhage, and thoracic negative pressure was
reestablished by removing all the air from the chest through a suction system connected
to the thoracoscope cannula. Lung reinflation was observed through the telescope, which
was retracted as inflation occurred. Skin incisions were closed using # 0 PDSh in a
horizontal mattress pattern. Duration of surgery was recorded and the procedure was
digitally recorded on videotape for subsequent viewing. Images in this thesis are

presented in color.

Tissue Processing

The line of staples was removed from biopsy specimens. The tissue samples were
immediately fixed by immersion in a solution of phosphate-buffered 4% formalin at the
time of biopsy and stored in a large volume of this fixative for at least twenty-four hours
until further processing for light microscopy. The fixed specimens were embedded in
either paraffin or plastic (glycol methacrylate°) and sectioned at a thickness of 5-6

microns or 1-2 microns, respectively. All of the sections were stained with hematoxylin

and eosin prior to microscopic examination by the study pathologist (JRH).

56

Statistical analysis

A two-factor repeated measures ANOVA was used to evaluate the effects of time
and horse groups. When significant differences (p < 0.05) were detected, post hoc
comparisons were made using the Student-Newman-Keul’s test. To compare values
between and within groups at specific intervals, a t-test and one-way repeated measures
AN OVA were used. Hematology values were also evaluated by two-factor repeated
measures AN OVA to evaluate the effects of time and groups and compare values before
and after surgery. Statistical analyses were performed by means of a computer software

program”. Significant difference was set at p < 0.05.

Results

There was excellent visibility of intrathoracic structures in all thoracoscopies, the
desired biopsy specimen was easily identified, and specimens were successfully obtained
in all horses. Three horses demonstrated minor signs of discomfort (agitation,
restlessness, and decreased level of sedation) during manipulation of the rigid telescope.
These signs were rapidly abolished after infusing additional local anesthetic deeper at the
incision sites in these three horses and subsequently in the remaining horses. Using the
mentioned portal sites, good manipulation of instruments was possible. In the first two
horses, one trochar required repositioning for better tissue handling. During surgery, the
lung did not collapse as well in heaves-affected'horses as it did in control horses, but that
did not limit our ability to obtain the biopsy. The endoscopic staple device provided

excellent hemostasis, was very easy to handle, and never misfired. No intra-operative

57

complications were noticed during any of the surgeries. The mean surgical time was 28 i

5 minutes.

Pulmonary function

There was a significant group difference in respiration rate between heaves-
affected (28.6 i 10.3 breaths/min) and control horses (17.4 i 6 breaths/min) and a
significant effect of time. With respect to baseline, there was a significant decrease in
respiration rate that began following sedation and persisted throughout the protocol (Fig
3). Examination of the data shows that the decrease in respiration rate was greater in
control than in heaves-affected horses. Indeed, when the data were evaluated by one-way
repeated-measures AN OVA, the decrease in respiration rate was significant in controls
but not in heaves-affected animals. Arterial pH and PaCOz did not change over time and
there was no difference between groups (Fig 3). There was no significant difference in
PaOz between groups; however, the mean Pa02 of heaves-affected horses showed a trend
(P = 0.06) to being lower than controls at all times. Pa02 had a tendency to decrease
following administration of detomidine and butorphanol. Immediately after the biospy
sample was taken, mean P302 was 70.9 113.3 mmHg and was significantly lower than
at baseline (86.8 i 10.9 mmHg), after sedation (81.2 i 12.6), after pneumothorax (81.7 i
12.9 mmHg ) and before biopsy (79.1 ;1; 13.7). Once the lung was re-inflated, PaOz
increased significantly (81.7 :13 mmHg Pa02 alter reinflation) and was no longer
different from baseline. The lowest PaOz (53 mmI-Ig) was recorded in a 21-year-old

heaves-affected horse immediately after the biopsy.

58

Cardiovascular fimction

Mean systemic arterial pressures did not change over time as a result of the
surgical procedure but there was a significant difference between groups. Heaves-
affected horses had a lower mean systemic arterial pressure (95 i 16.2 mmHg) than
controls (119 1 15.34 mmHg) (Fig 4). Pulmonary arterial pressures did not change over
time and there was no difference between groups (Fig 4). When compared to baseline,
heart rate decreased significantly following sedation and remained lower than baseline

throughout the procedure. There was no significant difference in heart rate between

groups.

Post-operative evaluation

All but one horse recovered after thoracoscopy without major postoperative
complications such as hemothorax, tension pneumothorax, pulmonary edema. With the
exception of the horse that developed hemothorax, the other nine horses never showed
signs of pain and/or discomfort after surgery. Two hours after surgery, one horse became
uncomfortable, sweated, and had tachycardia with pale mucous membranes. Follow-up
thoracic radiographs and ultrasound examination revealed excessive fluid accumulation
in the cranio-ventral aspect of the thorax. A thoracocentesis supported the diagnosis of
hemothorax. Intravenous isotonic fluids (20 liters bolus followed by 60ml/kg/24 hours
for 2 days), antibiotics (ampicillin trihydratei 10 mg/kg IV q 8 h and gentomicin sulfatej
6.6 mg/kg IV q 24 h for 10 days), and non-steroidal anti-inflammatory drugs (flunixin
meglunrine 1 mg/kg q 12 hours for 5 days) were administered. The horse's condition

continued to improve, and normal attitude, appetite, heart rate, and respiratory rate were

59

noticed on day 4 after surgery. An ultrasonographic examination of the thorax performed
on day 14 after biopsy did not reveal any evidence of pleural effusion. Recovery was
uneventful. Another horse showed a residual pneumothorax on the 2-hour postoperative
radiographic evaluation. The pneumothorax resolved 48 hours after surgery without any
intervention or complication. This horse never developed respiratory distress.

When comparing pre-surgical arterial pH, PaCOz, Pa02, with values obtained 2
and 48 hours after surgery, there were no significant differences over time and between
groups. The mean total white blood cells count 48 hours after surgery was lower than
before surgery and 14 days after surgery (Table 1). However, no difference between the
two groups was observed. In addition, a significant difference was found between groups
in fibrinogen values (heaves-affected: 0.35 1.15 gm/dl, controls: 0.28 1.08 gm/dl)
(Table 1). However, the range and mean values for both total white blood cell count and

fibrinogen were within normal.

Biopsy samples and histopathology

BiOpsy samples were 4x3x2 cm in size and weighed 1.53 1 0.92 grams and were
judged subjectively to be adequate for histological examination of the puhnonary tissue.
Most of the specimens consisted of a triangular section of peripheral lung tissue bordered
on two sides by pleura and on one side by compressed alveolar parenchyma adjacent to
the suture site. Besides the small amount of compressed alveolar parenchyma and
occasional associated hemorrhage near the suture, the biopsy specimens contained no
histologic artifacts due to the sampling or processing procedures (Fig 5a). Most of the

alveolar parenchyma was well aerated, which allowed for unhindered examination of

60

alveolar septa, alveolar ducts, preterrninal and terminal bronchioles, and pulmonary
vessels. Interestingly, a few samples also contained cross-sectional or longitudinal
profiles of small bronchi with intramural cartilage. Both paraffin- and plastic-embedded
sections were suitable for histopathologic evaluation (Fig 5b). The thinner (1-2 micron
thick) plastic-embedded sections provided excellent cellular detail due to the elimination
of overlapping cellular profiles (Fig 5b).

Puhnonary biopsies from horses with clinically documented heaves were
characterized by small airway lesions consisting primarily of mild to marked chronic
bronchiolitis with adjacent overdistention of alveoli and alveolar dusts (hyperinflation)
and/or alveolar fibrosis (Fig 6). Affected bronchioles contained hyperplastic surface
epithelium with numerous mucous goblet cells, lurninal accumulation of secreted mucus
with or without inflammatory cells (mainly neutrophils with lesser numbers of
mononuclear cells), and a mixed inflammatory cell infiltrate of lymphocytes, plasma

cells, and neutrophils in the peribronchiolar interstitiurn.

2nd thoracoscopy: 14-dayfollow-up

When the biopsy site and thorax were re-examined two weeks after surgery, the
thorax and lung were in excellent condition. There were no intrathoracic adhesions and
there was focal visceral pleural fibrosis at the biopsy site. All of the biopsy sites were
considered to have healthy granulation tissue and normal wound contraction.
Thoracoscopy of the horse that had developed hemothorax revealed a large hematoma at
the area of the central tendon of the diaphragm, presumably the site of origin of the

internal bleeding. The injury most likely happened while placing one of the

61

fl

trochar/cannula systems. Another thoracosc0pic examination was performed in this
horse 4 weeks after surgery. This revealed resolution of the hematoma and minor

fibrinous tags on the diaphragm at the site of injury.

Discussion

In the present study, a thoracoscopic lung biOpsy was safely conducted in
standing sedated horses with the aid of thoracoscopy by means of commercially available
endoscopic staples. All horses survived the surgery and, with the exception of one, all
animals recovered well without major complications. Although the use of thoracoscopy
has been reported in veterinary medicine, there are few reports of thoracoscopic surgery

10-14

in horses. Furthermore, a technique for thoracoscopic pulmonary wedge resection in

the horse has never been reported. Working in our institution, Peroni et al. demonstrated

14 The intention

that thoracoscopy is a very safe procedure in the healthy, sedated horse.
of the study reported here was to determine if thoracoscopy could be used to acquire lung
tissue samples adequate for histological evaluation with minimal post-operative
complications. Because lung biopsy is most likely to be performed in animals with
compromised lung function, we evaluated the technique in horses with pulmonary disease
in addition to animals with normal lungs. As our animal disease model, we used heaves-
affected horses in remission.

As has been observed by others,”’15 the administration of detomidine HCl and
butorphanol to the horses caused a decrease in respiratory rate. However, significant

hypoxemia only occurred immediately after lung biopsy, especially in the heaves-

affected horses. This hypoxemia was transient and was due to ventilation/perfusion

62

mismatch rather than to hypoventilation (PaCOz remained constant).
Ventilation/perfirsion mismatch was not simply the result of pneumothorax and sedation
but was the result of the additional procedures necessary to obtain the biopsy. During this
phase of surgery, manipulation of instruments in and out of the chest was frequent, which
probably allowed more movement of air into the pleural cavity, thus worsening the
pneumothorax.

Horses with heaves have diffuse airway obstruction, some of which may persist
during clinical remission. ‘6 This was reflected by our observation that horses with
heaves tended to have a lower Pa02 than controls. Even though the heaves-affected
horses had compromised lung function, their decrease in Pa02 after biopsy was no greater
than that of controls. In the heaves-affected animals, therefore, the baseline level of Pa02
rather than the complications of the biopsy procedure determined the Pa02 immediately
after lung biopsy.

The cardiovascular changes associated with thoracoscopy were minimal and
mainly due to the negative effects of detomidine on heart rate. Despite the decreased
heart rate, and presumably cardiac output, systemic and pulmonary vascular pressures
were maintained.

Throughout the study, heaves-affected horses showed lower mean systemic
arterial pressures than controls. This result contradicts those of Nyman et al., who found
no difference when comparing systemic arterial pressures in normal horses and horses
affected by heaves.l7 Unlike the situation in our study, the heaves-affected horses of
Nyman et al. were showing clinical signs at the time that pressure measurements and

values were compared to values of normal horses. In the present study, the lack of

63

difference in heart rate ruled out the possibility of a more profound effect of detomidine
in the heaves-affected horses. We speculate that the difference between groups was
caused by a greater stress effect and increased sympathetic tone in the control horses,
which were new to the laboratory environment and naive to experimental procedures. By
contrast, our heaves-affected horses were well adapted to research procedures, such as
pulmonary fimction testing.

In the present study, minor signs of discomfort were noticed during the surgery in
three of the ten horses. As previously observed and described by Peroni et al., the source
of pain in these horses was excessive distraction of ribs while moving the telescope
and/or instruments.18 Deeper infusion of the local anesthetic at the incision site
dramatically reduced the discomfort caused by manipulation of the instrument in these
three horses, and subsequently, in the remaining horses. Diffusion of lidocaine into
deeper structures may have desensitized the non-myelinated C-fibers of the pleura, thus
providing better local analgesia. Due to the minimally invasive nature of the procedure
and the analgesia created by local anesthetics that likely lasted into the postoperative
period, the horses level of comfort and behavior after surgery was similar to the level
prior to surgery in all of the horses except the one that deveIOped hemothorax. When
thoracoscopic surgeries are performed, major muscles are not divided, ribs are not spread,
dislocated, or broken, and ligaments, nerves, and blood vessels are not severely
damaged.2 The avoidance of these adverse events leads to an accelerated recovery and
reduced postoperative pain. F urtherrnore, the small intercostal incisions do not seem to
contribute to postoperative pain and ventilation dysfunction, as the thoracic cage is not

severely traumatized.2

With the exception of one horse, all of the horses recovered well from the surgery.
Physical examinations, hematology values, thoracic radiographs, and ultrasound images
were normal at the follow-up postoperative evaluations, indicating no adverse clinical
manifesation from the procedure. The follow-up thoracoscopy showed normal wound
healing and no intra-thoracic adhesions. The horse that developed hemothorax was the
only one that had small fibrinous tags at the site of injury.

Inadvertent injury to the diaphragm while inserting a trochar/cannula system
caused the hemothorax found in one horse. The injury occurred while placing the
telescope portal at intercostal space 16. At this level, the space between the diaphragm
and the thoracic wall is minimal. After reviewing the video of this horse’s surgery, we
could not detect any hemorrhage and/or site of injury. We hypothesize that at the time of
the injury, the horse did not bleed because of the effect of pneumothorax on the vessels
supplying the diaphragm. The increase in pleural pressure during pneumothorax probably
increased the vascular transmural pressure, causing the diaphragmatic vessels to collapse.
As soon the negative pressure was reestablished, the vessels probably opened and
hemorrhage began. The horse was treated and observed for 10 days. Recovery was
uneventful. Injury to vital organs can be avoided by 1) induction of pneumothorax to
completely collapse the ipsilateral lung before insertion of trochars; and 2) direct
thoracoscopic observation during insertion of instrument portals and during manipulation
of instruments and organs.

One horse developed radiographic signs of pneumothorax two hours after surgery.
Because the horse lacked signs of respiratory distress, it is our opinion that the

pneumothorax was due to failure to fully reinflate the lung rather than to air leakage at

65

the biopsy site. Prolonged air leakage from the pulmonary resection is the most comrhon
complication of thoracoscopically guided lung biopsy in humans and is accompanied by
respiratory distress due to the tension pneumothorax. 19’ 20 Air leakage is found more
often in patients with interstitial pulmonary diseases treated preoperatively with
steroids.19 This is a very important point to remember if using this technique in horses
undergoing steroid treatment.

The use of commercially available endoscopic staples facilitated the resection of
the puhnonary tissue. The instrument provided excellent hemostasis at the pulmonary and
biopsy incision sites, was easy to handle, and never misfired. If a larger tissue sample is
desired, multiple wedge excisions can be employed. Other techniques of lung biopsy
using endoscopic endoloops have been described for both humans and dogs. 21’ 22
However, hemorrhage because of slippage of the endoloop is a reported complication.
Therefore, the authors believe that it is better to use the endoscopic staple/cutter.

In humans, thoracoscopic pulmonary wedge resection is becoming the procedure
of choice to obtain a lung biopsy sample for the diagnosis of many lung diseases and as
an adjunct to conventional respiratory diagnostic tests. 19’ 21’ 23 The main advantage of
thoracoscopic surgery over the open thoracotomy technique is the minimally invasive
nature .of the procedure. Human patients undergoing thoracoscopic. surgery for lung
biopsy and/or peripheral lung resection have less morbidity and post-operative pain,
shorter post-operative stays in hospital, and need less intensive medical care.
Thoracoscopic pulmonary wedge resection is preferable to other techniques because it

allows removal of large tissue samples from multiple segments of the lung and resection

of wide surgical exposure, and it leads to little post-operative trauma.4

66

Examination of biopsies confirmed the presence of adequate pulmonary
architecture with minimal artifacts. Unlike percutaneous and transbronchial lung biopsy,
thoracoscopic wedge resection provides an excellent tissue sample for both histologic and
microbiologic examination. An advantage of surgical biopsies is that the specimen
obtained can contain both normal and diseased tissue. Direct observation of the surgical
procedure and excellent hemostasis avoid complications reported by others when
performing percutaneous lung biopsies. 9 F urtherrnore, multiple resections can be
performed or larger wedge resections obtained if necessary. The main disadvantage of
this technique is that the biopsy sample is limited to the periphery of the lung. Therefore,
the biopsy sample will be useful only for peripheral lesions or diffuse interstitial diseases.
In some instances, puhnonary lesions located on the broad surface of the lung may not be
amenable to pulmonary wedge resection with an endoscopic stapler. Such lesions can be
seen during thoracoscopy, and biopsy can be performed with fine needle aspirates,
endoscopic biopsy forceps, tru-cut biopsy instruments, or neodynimnzyttriurn-aluminium-
garnet laser (NszAG) to yield a diagnostic sample. In humans, the Nd:YAG laser is
frequently used as an adjunct to the stapler and for control of bleeding and air leaks.21

In conclusion, thoracoscopically guided pulmonary wedge resection is safe and
well tolerated in horses, and provides a minimally invasive method for lung biopsy in
horses. The procedure can be used for both clinical diagnosis and pulmonary research.
Careful surgical technique will prevent injury to vital organs. We believe that this

procedure deserves additional evaluation in clinical situations and for research purposes.

67

Manufacturers' addresses

aAngiocath, Becton Dickinson, Sandy, Utah, USA

bInsyte, Becton Dickinson, Sandy, Utah, USA

CColburn Instruments (model Ll9-69)Allentown, Pennsylvania, USA
dNova Biomedical, Waltham, Massachusetts, USA

°Storz Veterinary Endoscopy, Santa Clara, California, USA

f Stryker Quantum 3000, Santa Clara, California, USA

gSony Electronics, Inc. New York, New York, USA

hEthicon Endo-Surgery, Inc., Cincinnati, Ohio, USA

iArnpicillin, Apothecon, Princeton, New Jersey, USA

jGentocin, Boehringer Ingelheirn, Inc., St. Joseph, Missouri, USA
kBanamine, Schering Plough, Kenilworth, New Jersey, USA
lDormosedan, Pfizer Animal Health, Exton, Pennsylvania, USA
rr'Torbugesic, Fort Dodge, Iowa, USA

"Carbocaine, Sanofi-Winthrop, New York, New York, USA
°Irnmuno-BedEl, Electron Microsc0py Sciences, Ft. Washington, Pennsylvania, USA

pSigma Stat 2.03, San Rafael, California, USA

68

REFERENCES FOR CHAPTER 2

69

REFERENCES FOR CHAPTER 2

1. Shrager JB, Kaiser LR. Thoracoscopic lung biopsy: Five commonly asked questions
about video-assisted thoracic surgery. Post Grad Med 1999;106:139-152.

2. Lewis RL, Caccavale RJ, Sisler GE, et al. One hundred consecutive patients
undergoing video-assisted thoracic operations. Ann Thorac Surg1992;54:421-426.

3. Miller DL, Allen MS, Trasteck VF, et al. Videothoracoscopic wedge excision of the
lung. Ann Thorac Surg 1992;54:410-414.

4. Mack MJ, Aronoff RJ, Acuff TE, et al. Present role of thoracoscopy in the diagnosis
and treatment of diseases of the chest. Ann Thorac Surg 1992;54:403-409.

5. Traub-Dargatz J L, Salman MD, Voss J L. Medical problems of adult horses, as ranked
by equine practitioners. J Am Vet Med Assoc199l;198:1745-1747.

6. Muir T. Diagnostics techniques for the lower respiratory tract diseases. In: Robinson
NE, ed. Current Therapy in Equine Medicine 3. Philadelphia, PA: WB Saunders;
1992:302-303

7. Raphael CF, Gunson DE. Percutaneous lung biopsy in the horse. Cornell Vet
1981;71:439-448.

8. Shatzmann U, Straub R, Gerber H. Percutaneous lung biopsy in the horse. Vet Rec
1974;94:588-590.

9. Savage CJ, Traub-Dargatz J L, Mumford EL. Survey of the large animal diplomates
of the American College of Veterinary Internal Medicine regarding percutaneous lung
biopsy in the horse. J Vet Intern Med 1998;12:456-464.

10. Ford TS, Vaala WE, Sweeney CR, et al. Pleuroscopic diagnosis of gastroesophageal
squamous cell carcinoma. J Am Vet Med Assoc 1987;190:1556-1558.

ll. Mueller PO, Morris DD, Carmichael KP, et al. Antemortem diagnosis of
cholangiocellular carcinoma in a horse. J Am Vet Med Assoc 1192;201:899-901.

12. Rossier Y, Sweeney CR, Heyer G, et al. Pleuroscopic diagnosis of disseminated
hemangiosarcoma in a horse. I Am Vet Med Assoc 1990;196:1639-1640.

13. Vachon, AM, Fisher AT. Thoracoscopy in the horse: diagnostic and therapeutic
indications in 28 cases. Equine Vet J 1998;30:467-475.

70

l4. Peroni JF, Robinson NE, Stick J A, FJ Derksen. Pleuropuhnonary and cardiovascular
consequences of thoracoscopy performed in healthy standing horse. Equine Vet J
2000;32:280-286.

15. Lavoie JP, Phan TH, and Blais D. Effects of a combination of detomidine and
butorphanol on respiratory function in horses with or without chronic obstructive
pulmonary disease. Am J Vet Res 1996;57:705-709.

16. Robinson NE, Derksen FJ, Olszewski MA, et al. The pathogenesis of chronic
obstructive pulmonary diseases in horses. Br Vet J 1996;152:283-305.

17. Nyman G, Linderberg R, Weckner D, et al. Pulmonary gas exchange correlated to
clnical signs and lung pathology in horses with chronic bronchiolitis. Equine Vet J
1991 ;23:253-260.

18. Peroni JF, Homer NT, Robinson NE, Stick JA. Equine thoracoscopy: normal
anatomy and surgical technique. Equine Vet J 2001 ;33:23 1-237.

19. Krasna MJ, White CS, Aisner SC. The role of thoracoscopy in the diagnosis of
interstitial lung disease. Ann Thorac Surg 1995;59:348-351.

20. Krasna MJ, Deshmukh S, Mc Laughlin J S. Complications of thoracoscopy. Ann
Thorac Surg 1996;61:1066-1069.

21. Stanley DG. Video thoracoscopic resection of primary lung lesions. In: Dieter RA,
Thoracoscopy for surgeons: diagnostics and therapeutics. New York, NY: Igaku-Shoin
1995: 90-148.

22. Faunt KK, Jones PD, Turk, JR, et al. Evaluation of biopsy specimen obtained during
thoracoscopy from lungs of clinically normal dogs. Am J Vet Res 1998;59:1149-1152.

23. McKeown PP, Conant P, Hubbell DS. Thoracoscopic lung biopsy. Ann Thorac Surg
1992;54:490-492.

71

Table 1 — Total and differential white blood cell count, packed cell volume, total protein,
Pa02, PaCOz, and pH before surgery (baseline), 2 hours after surgery, 48 hours after
surgery, and 14 days after surgery for both groups of horses (controls and heaves). Data
are means 1 sd. ;* significantly different (p < 0.05) from baseline; + significantly

different (p < 0.05) between groups.

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Figure l—Diagrarn showing the position of portals to perform a thoracoscopic pulmonary
wedge resection in a horse. lSt portal: telescope portal, intercostal space 13th ventral to
epaxial muscles; 2nd portal: endoscopic staple/cutter; intercostal spaces 11 or 12 about 15
cm ventral to first portal, and 3rd portal: atraumatic Babcock forceps, intercostals space

15, 10 cm ventral to the 1st portal; red circle represents the selected site for lung biopsy.

74

Figure 2-Technique for thoracoscopic pulmonary wedge resection. Top left: The biopsy
site is grasped with atraumatic Babcock forceps; Top right: Endoscopic staple/cutter
crossed over and clamped the puhnonary wedge; Bottom left: Biopsy sample obtained
after pulmonary wedge resection; Bottom right: Pulmonary site after wedge resection

showing good hemostasis.

76

 

Figure 2

Figure 3—Effects of detomidine and thoracoscopic lung biopsy on respiration
rate, Pa02, PaCOz, and arterial pH. Data are expressed at mean 1 s.e.m; * =
significantly difference (p<0.05) from baseline; 1; = significantly difference
(p<0.05) between groups. Grey bars = control animals, Red bars = heaves-
affected horses. Immediately after the biopsy (post biopsy), mean Pa02 decreased
significantly and became lower than at baseline, after sedation, after
pneumothorax and before biopsy. Once the lung was re-inflated, Pa02 increased

significantly and was no longer different from baseline.

 

Rap. (Melanin)

P102 (mmHg)

P8002 (mmHg)

 

Figure 3

Figure 4—Effects of thoracoscopic lung biopsy on mean heart rate and systemic and
pulmonary arterial pressures. Data are expressed at mean 1 s.e.m.; * = significantly
difference (p<0.05) from baseline; 1 = significantly difference (p<0.05) between groups.

_ Gray bars = control animals, Red bars = heaves-affected horses.

80

HR (boatsIman

 

140
120
100

MAP (mmHg)

 

PAP (mmHg)

 

Figure 4

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Figure S-Light photomicro graph of 1-2 micron sections from lung biopsy samples taken
from control (A and C) and heaves-affected (B and D) horses in clinical remission.
Figures A and B, bar = 500 microns; figures C and D, bar = 100 microns, H & E stain. a
= alveolar parenchyma, b = bronchioles, p = pleura. Figure A, note the well-preserved
alveolar parenchyma and the compression of the parenchyma close to the staple line
(arrow). The high magnification of alveolar parenchyma from a control horse (figure C)
shows individual capillaries containing erythrocytes (arrow). The low magnification
photomicrograph fiom a heaves-affected horse shows peribronchial thickening. Figure D
shows peribronchial interstitial fibrosis with epithelial hyperplasia and mucous cell

metaplasia (arrows) in a heaves-affected horse.

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Figure 5

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Figure 6—Light photomicrograph of 1-2 micron sections of bronchioles from lung biopsy
samples taken from a control (A) and a heaves-affected (B) horse. Epithelium (e) and
smooth muscle (sm) are clearly visible, as are mucous accumulation in the airway lumen
(open arrow) and mild peribronchial inflammation (dark arrow) in the heaves-affected

horse. Bar = 50 microns, H & E stain.

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Figure 6

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SUMMARY, CONCLUSIONS AND FUTURE INVESTIGATIONS

This research demonstrated that thoracoscopically guided lung biopsy provided a
minimally invasive and effective method to obtain lung biopsy specimens in both normal
horses and horses with chronic pulmonary disease. Examination of biopsies demonstrated
excellent preservation pulmonary architecture with minimal artifacts. This technique will
be useful only for peripheral pulmonary lesions or diffuse pulmonary diseases because
the biopsy sample is limited to the periphery of the lung. Since we were able to
demonstrate the safety of thoracoscopic pulmonary biopsy, we believe this technique
deserves further investigation in pulmonary research and its use in clinical situations
should be encouraged.

Thoracoscopically guided lung biopsy provides excellent tissue samples suitable
to study equine pulmonary diseases such as heaves and exercise-induced pulmonary
hemorrhage. Biopsy samples can be utilized to observe and measure inflammatory and
airway remodeling changes using electron microscopy, immuno-histochemistry, and in
situ hybridization. The trafficking of cytokines and responsiveness to induced antigens,
and treatment modalities (e.g., steroids and bronchodilators) can be evaluated by direct
methods using a biopsy specimen, thus decreasing the number of horses killed for
research. Before using this biopsy sample to study the airways, we have to answer a
simple question: how representative is this puhnonary sample from the whole lung? We
hypothesize that the biopsy sample obtained by this technique is an excellent
representation of the lung tissue, but future investigations should objectively answer this

question.

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Operative thoracoscopic procedures in horses are technically feasible and are
associated with numerous advantages, including diminished postoperative pain and
morbidity. Although thoracoscopic procedures in equine surgery are still in the
developmental phase, I anticipate that the trend toward clinical application will escalate.
Future investigations regarding thoracoscopy in horses should be conducted: a) to
evaluate the effects of multiple thoracoscopic lung biopsies performed during consecutive
days, b) to evaluate thoracoscopic surgery performed under general anesthesia and single
lung ventilation, c) and to develop thoracoscopic surgical techniques for the treatment of
diaphragmatic hernias and congenital vascular anomalies in horses.

In conclusion, thoracoscopic pulmonary biopsy has been shown to be an effective
and safe method for lung biopsy in horses. This new technique may be applicable for the

diagnosis and treatment of pleuropulmonary diseases in horses.

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