Page 395 - Small Animal Internal Medicine, 6th Edition

CHAPTER 23 Clinical Manifestations and Diagnostic Tests of Pleural Cavity and Mediastinal Disease 367

gravity-dependent sites (i.e., closer to costochondral junc- removed, except in patients with acute hemothorax (see
tions) and air from nondependent sites. Thoracic radio- Chapter 25).
VetBooks.ir graphs are useful in choosing sides for thoracocentesis in THORACOSCOPY AND THORACOTOMY
the event of unilateral effusion. Ultrasonography is useful for
guiding needle placement in patients in which fluid collection
proves difficult. A definitive diagnosis for the cause of pleural effusion is
A local anesthetic can be administered at the site of tho- sometimes elusive. In such cases, thoracoscopy or thora-
racocentesis. Sedation is rarely required but may be useful cotomy may be necessary to allow visual assessment of
for decreasing patient stress. The site is shaved and surgically the thoracic cavity and the collection of specimens for
prepared, and the procedure is performed using sterile tech- histologic and microbiologic analysis. Mesotheliomas and
nique. Most often, a butterfly catheter, a three-way stopcock, pleural carcinomatosis are often diagnosed through these
and a syringe are used. Removal of fluid or air by syringe is methods.
associated with movement of the syringe, and the tubing of
the butterfly catheter prevents this movement from affecting
the position of the needle within the thoracic cavity. Air and CHEST TUBES: INDICATIONS
most fluids can be retrieved through a 21-gauge butterfly AND PLACEMENT
catheter. A larger needle may be required to collect extremely
viscous fluids, such as fluid from FIP or pyothorax. The Chest tube placement is indicated for the management of
three-way stopcock is attached to the catheter to keep air pneumothorax, if air continues to accumulate despite mul-
from entering the thorax during emptying or changing of tiple thoracocenteses, and for the treatment of dogs and
the syringe. cats with pyothorax (see Chapter 24). If possible, needle
With the syringe snugly attached and the stopcock open thoracocentesis and therapy for shock are performed to sta-
between the catheter and the syringe (closed to room air), bilize dogs and cats in critical condition before chest tubes
the needle is advanced through the skin only. The needle and are placed.
the skin are then moved about two rib spaces to the actual The major complication of chest tubes is pneumothorax
collection site. This technique prevents air from entering the caused by a leak in the apparatus. Animals with chest tubes
chest through the needle tract after the procedure (an must be carefully monitored at all times to make sure that
unlikely scenario). The needle is then advanced into the they do not disrupt the tubing connections, pull the tube
thorax immediately in front of the rib to avoid the intercostal part of the way out of the chest so that there are fenes-
vessels and nerves. The needle is held with a hand resting on trations outside the body wall, or bite through the tubing.
the chest wall so it will not move relative to respirations or Any leaks in the system can result in a life-threatening
movement of the animal. Slight negative pressure is applied pneumothorax within minutes. If an animal with a chest
to the catheter by the syringe so that entry into the pleural tube must be left unattended, the tube should be clamped
space is immediately identified by the recovery of fluid or air. off close to the body wall and should be well protected
Once the needle has entered the pleural space, the tip is by bandage material. Hemothorax or pneumothorax can
aimed away from the lung by lowering the wings of the be caused by lung laceration during tube placement. Iat-
catheter toward the body wall. Ideally, the bevel of the needle rogenic pyothorax can result from bacteria introduced
should face toward the lungs. during placement or gaining entrance to the chest through
An alternative to a butterfly catheter is an intravenous the tube itself while it is in place. These complications are
over-the-needle catheter. In large dogs a 3 4 or 5 4 (8- or generally prevented through careful techniques and aseptic
1
1
13-cm) 14- to 16-gauge catheter can be used. These catheters practices.
are soft and produce less trauma than is produced by but- Pediatric chest tubes can be obtained from hospital supply
terfly catheters while in the pleural space; they permit the companies. These tubes have multiple fenestrations, are cali-
animal to be repositioned or rolled to improve fluid or air brated along their length, and are radiopaque. For treating
removal. The longer length, compared with a butterfly pyothorax, the tube should be as large as will fit between the
needle, may be needed to reach the pleural space in large- ribs. The size of the tube is less critical for control of pneu-
breed or obese dogs. Extension tubing and a three-way stop- mothorax. Before placement, the end of the tube is occluded
cock are attached to the catheter immediately after placement. with a syringe adapter, a three-way valve, and a hose clamp
A small skin incision, just slightly larger than the catheter, (Fig. 23.5, A).
will facilitate placement. As with the butterfly catheter, slight Sterile technique is used during placement of the chest
negative pressure is maintained by the syringe so that entry tube. In an animal with unilateral disease, the tube is placed
into the pleural space is immediately identified. The catheter in the involved side of the thorax. Either side can be used in
tip is then directed cranially to allow positioning of the cath- an animal with bilateral disease. The lateral side of the animal
eter between the lungs and the chest wall, preventing trauma over the caudal rib cage is shaved and surgically prepared.
to the lung tissue. The animal is anesthetized or heavily sedated. If the animal
After fluid specimens are saved for cytologic and is sedated, a local anesthetic is placed subcutaneously at the
microbiologic analysis, as much fluid or air as possible is tenth ICS and within the subcutaneous tissues, intercostal