Page 399 - Small Animal Internal Medicine, 6th Edition

CHAPTER 24
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Disorders of the Pleural

Cavity and Mediastinum

PYOTHORAX Identification of a septic exudate by pleural fluid analy-
sis establishes the diagnosis of pyothorax. Septic suppura-
Etiology tive inflammation is a consistent finding in pleural fluid
Septic exudate in the pleural cavity is referred to as pyotho- examined cytologically, except in animals receiving antibi-
rax. It is most often idiopathic in origin, particularly in cats. otics (Fig. 24.1; see also Chapter 23). Pleural fluid should
Barrs et al. (2009) propose that the source of organisms in be further evaluated by Gram staining, and aerobic and
these cases is the oropharynx. Pyothorax can result from anaerobic bacterial cultures. These tests may identify organ-
foreign bodies, puncture wounds through the chest wall, isms not apparent by routine cytologic staining and may
esophageal tears (usually from ingested foreign bodies), and provide valuable information for antibiotic selection. Anaer-
extension of pulmonary infection. Thoracic foreign bodies obes are usually present in the fluid, and in many dogs and
are usually migrating grass awns. They are rare in cats and cats more than one type of bacteria is present. All of the
are most common in sporting breeds of dogs in states where types of bacteria involved may not grow in the laboratory in
there is a large concentration of foxtail grasses (e.g., spite of cytologic evidence of their presence, possibly because
California). of competition between organisms or an inhibitory effect
of the exudative fluid. Organisms such as Actinomyces and
Clinical Features Nocardia particularly do not grow well if specimens have
Dogs and cats with pyothorax have clinical signs referable to been cultured using routine procedures, and the labora-
a closed site of infection (abscess) and pleural effusion. Signs tory should be notified of the possibility of these organisms.
may be acute or chronic. Tachypnea, decreased lung sounds, Absence of growth of bacteria does not rule out a diagnosis
increased abdominal excursions, and paradoxical breathing of pyothorax.
(abdomen and chest expanding asynchronously) are typical Evaluation of the patient’s systemic status may reveal
of pleural effusion. In addition, fever, lethargy, anorexia, and evidence of active inflammation, systemic inflammatory
weight loss are common. Animals may be presented in septic response syndrome, or sepsis. A normal leukogram does not
shock or may demonstrate signs of systemic inflammatory rule out the possibility of pyothorax.
response syndrome.
Treatment
Diagnosis Medical therapy for pyothorax includes antibiotics, drainage
The diagnosis of pyothorax is made through thoracic radi- of the pleural cavity, and appropriate supportive care (e.g.,
ography and cytologic evaluation of pleural fluid. Thoracic fluid therapy). At first, empirically selected antibiotics are
radiographs are used to confirm the presence of pleural effu- administered intravenously. Results of Gram staining and
sion and to determine whether the disease is localized, uni- culture and sensitivity testing are helpful in adjusting antibi-
lateral, or bilateral. In most animals, fluid is present otic protocols as they become available. Recently published
throughout the pleural space. The finding of a localized accu- antimicrobial guidelines for the treatment of respiratory
mulation of fluid indicates the possible presence of pleural tract disease in dogs and cats (Lappin et al., 2017) recom-
fibrosis, mass lesions, or lung lobe torsion. Thoracic radio- mend initial treatment of an injectable fluoroquinolone (e.g.,
graphs are taken again after removal of the fluid to evaluate enrofloxacin or marbofloxacin) with a penicillin (e.g., ampi-
the pulmonary parenchyma for evidence of underlying dis- cillin with sulbactam) or clindamycin. The penicillin or
order (e.g., bacterial pneumonia, foreign body) that may clindamycin should be continued regardless of culture results
have caused the pyothorax. Ultrasonography is also useful because of the difficulty in growing some anaerobes in the
for identifying adhesions or pockets of fluid. laboratory.

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