Page 404 - Small Animal Internal Medicine, 6th Edition

376 PART II Respiratory System Disorders

pleural surfaces may respond to palliative therapy with intra- tube, and radiographic monitoring are indicated. If abnor-
cavitary infusions of cisplatin or carboplatin (Moore, 1992), mal radiographic opacities persist without improvement for
VetBooks.ir with or without concurrent chemotherapy. Placement of longer than several days in trauma patients, further diagnos-
tic tests should be performed, as described for spontaneous
pleuroperitoneal shunts or intermittent thoracocentesis to
alleviate the degree of respiratory compromise can be con-
over time may necessitate surgical intervention. Treatment
sidered to prolong the life of patients that have no clinical pneumothorax. Failure of resolution of the pneumothorax
signs beyond those resulting from the accumulation of with an autologous blood-patch has shown promise in
pleural effusion. patients for which surgery is not an option (Oppenheimer
et al., 2014).

PNEUMOTHORAX SPONTANEOUS PNEUMOTHORAX
Spontaneous pneumothorax is much less common than
Pneumothorax is the accumulation of air in the pleural traumatic pneumothorax and occurs more often in dogs
space. The diagnosis is confirmed by means of thoracic radi- than in cats. Thoracocentesis is useful for initial stabilization
ography. The pleural cavity is normally under negative pres- of the animal’s condition. If frequent thoracocentesis is
sure, which keeps the lungs expanded in health. However, if needed to control the pneumothorax, a chest tube is placed
an opening forms between the pleural cavity and the atmo- (see Chapter 23).
sphere or the airways of the lungs, air is transferred into the Dogs and cats are evaluated for underlying disease with
pleural space because of this negative pressure. A tension thoracic radiography (repeated after full lung expansion),
pneumothorax occurs if a one-way valve is created by tissue computed tomography of the thorax, multiple fecal examina-
at the site of leakage, such that air can enter into the pleural tions for Paragonimus ova (see Chapter 20), heartworm
space during inspiration but cannot return to the airways or testing, and possibly tracheal wash fluid analysis or bron-
atmosphere during expiration. Increased intrapleural pres- choscopy. Computed tomography is much more sensitive for
sure and resultant respiratory distress occur quickly. the identification of bullae and should be performed before
Leaks through the thoracic wall can occur after a trau- thoracotomy. In a study by Au et al. (2006), thoracic radiog-
matic injury or as the result of a faulty pleural drainage raphy identified bullae or blebs in only 2 of 12 dogs with
system. Air can also enter the thorax during abdominal spontaneous pneumothorax, whereas computed tomogra-
surgery through a previously undetected diaphragmatic phy was successful in identifying lesions in 9 of these dogs.
hernia. These causes are readily identified. Pneumothorax in patients with Paragonimus infection
Pneumothorax resulting from pulmonary air can occur may respond to treatment with anthelmintics (see Chapter
after blunt trauma to the chest (i.e., traumatic pneumotho- 22) and supportive therapy as described for traumatic pneu-
rax) or as a result of existing pulmonary lesions (i.e., spon- mothorax. Retrospective studies support surgical interven-
taneous pneumothorax). Traumatic pneumothorax occurs tion for most dogs with spontaneous pneumothorax. In a
frequently, and findings of the history and physical examina- review of 21 cases, Holtsinger et al. (1993) found that most
tion allow this to be diagnosed. Pulmonary contusions are dogs with spontaneous pneumothorax managed medically
often present in these animals. with chest tubes and suction ultimately required surgery
Less commonly, pneumothorax is a result of tracheal during initial hospitalization or upon subsequent recurrence
trauma. Tracheal tears within the thorax are usually the of pneumothorax to resolve the problem. Because unob-
result of overinflation of endotracheal tube cuffs, a particular served recurrence of spontaneous pneumothorax can be
concern in cats. Trauma to the cervical trachea more often fatal, conservative treatment is believed to carry greater risk
results in subcutaneous emphysema, though dissection of air than is associated with surgery. Furthermore, a report of 64
can occur into the mediastinum or thorax. cases by Puerto et al. (2002) showed that recurrence and
Spontaneous pneumothorax occurs when preexisting mortality rates for dogs with spontaneous pneumothorax
pulmonary lesions rupture. Cavitary lung diseases include were lower in dogs that had surgery compared with dogs that
blebs, bullae, and cysts, which can be congenital or idio- were treated conservatively. Similar data are not available to
pathic, or can result from prior trauma, chronic airway guide the management recommendations for cats with spon-
disease (particularly in cats), or Paragonimus infection. taneous pneumothorax, but supportive therapy is preferred
Necrotic centers can develop in neoplasms, thromboembo- for most cats. In a retrospective study of 35 cats, mortality
lized region (e.g., from dirofilariasis) abscesses, and granu- was high regardless of treatment, with only 19 cats (54%)
lomas involving the airways; these can rupture, allowing air surviving to discharge (Mooney et al., 2012). Only 1 of 5 cats
to escape into the pleural space. (See Chapter 20 for further that had thoracotomy survived.
discussion of cavitary lesions.) For patients undergoing thoracotomy, a median sternot-
omy is generally recommended to allow exposure of all lung
TRAUMATIC PNEUMOTHORAX lobes because it is often not possible to localize all cavitary
Dogs and cats with pneumothorax and a recent history of lesions preoperatively (Fig. 24.4). Abnormal tissue is evalu-
trauma are managed conservatively. Cage rest, removal of ated histologically and microbiologically for a definitive
accumulating air by periodic thoracocentesis or by chest diagnosis.