Journal Scan: Current concepts in the diagnosis and management of pyothorax

Why they did it

A lack of consensus exists on the appropriate approach to managing pyothorax in dogs and cats. Despite the many treatment options, the optimal therapeutic approach is unclear, and the prognosis for successful outcome is variable.

What they did

The authors present an overview of the current literature with respect to the pathophysiology, diagnosis and treatment of pyothorax in dogs and cats. They provide instruction for the placement of a small-gauge thoracic drain.

What they found

Pathophysiology. The origin of pyothorax often remains unknown in dogs and cats, but recent evidence suggests that parapneumonic spread-pleural infection arising as a result of pneumonia or lung abscess-may be the most common route of infection in cats. In dogs on the other hand, the cause of pyothorax may depend more on geographic region (e.g. migration of grass awns in endemic areas). The authors note that infection with feline leukemia virus or feline immunodeficiency virus has not been associated with pyothorax in cats.

Diagnosis. The introduction of bacteria and inflammatory cells into the pleural space and disruption of Starling's forces and lymphatic drainage that govern pleural fluid drainage lead to fluid accumulation. The authors discuss the need for cytologic analysis as well as aerobic and anaerobic bacterial culture of pleural fluid to provide a definitive diagnosis. Polymicrobial infections are common. Common aerobic organisms isolated from feline and canine pyothorax patients include Escherichia coli and Pasteurella, Actinomyces, Nocardia, Streptococcus, Staphylococcus and Corynebacterium species. Common anaerobic organisms include Peptostreptococcus anaerobius and Fusobacterium, Bacteroides, Prevotella and Porphyromonas species.

Sepsis may occur in up to 40% of cats with pyothorax, and cats may present with bradycardia and hypothermia. In addition to thoracic radiographic and ultrasonographic examinations, thoracic computed tomography may be beneficial in assessing patients with pyothorax and identifying the need for surgical intervention (e.g. foreign body, pulmonary abscess). Blood and pleural N-terminal pro-B-type natiuretic peptide (NT-proBNP) concentrations may be useful in differentiating cardiac from noncardiac causes of pleural effusion in cats, but the authors noted that overlapping values between these two groups limit the diagnostic utility of this test in cases of pyothorax.

Treatment. Antimicrobial therapy and thoracic drainage are considered the cornerstone of therapy for patients with pyothorax. Antibiotic selection should be based on culture and sensitivity data when at all possible. Broad-spectrum therapy to address both aerobic and anaerobic pathogens is recommended. Empiric therapy for dogs may include a potentiated penicillin in combination with a fluoroquinolone; monotherapy with a potentiated penicillin may be sufficient in cats. Intravenous administration should be considered until the patient is stable and eating; however, the optimal duration of therapy is unknown and is commonly two weeks past radiographic resolution of effusion.

Mechanical removal of infected pleural fluid is also integral to successful management, but there are no data in veterinary medicine as to which method is superior-needle thoracocentesis versus chest tube placement. Similarly, there is controversy regarding the utility of thoracic lavage or use of intrapleural medications. For patients with thoracostomy tubes, there is a lack of consensus on whether intermittent versus continuous drainage is best. Thoracotomy or video-assisted thorascopic surgery may be considered for patients in which there is an indication for surgery (e.g. foreign body) or for patients that do not appear to be responding to aggressive medical management. The ideal type and timing of surgical interventions, however, is unclear.

Take-home message

No evidence-based recommendations or consensus of opinion has been established on the best way to treat dogs and cats with pyothorax. The prognosis is variable, but good outcomes may be achieved with appropriate care. Patients that present with evidence of sepsis or respiratory decompensation have a worse prognosis.

Stillion JR, Letendre J. A clinical review of the pathophysiology, diagnosis, and treatment of pyothorax in dogs and cats. J Vet Emerg Crit Care 2015;259(1):113-129.

Link to abstract: http://onlinelibrary.wiley.com/doi/10.1111/vec.12274/abstract