Pyothorax in cats: treatment with drainage and lavage

Question

3-year-old intact male cat with outdoor access, presenting with dyspnoea, fever and anorexia. Thoracocentesis yields a turbid, foul-smelling fluid with abundant degenerate neutrophils and mixed intra- and extracellular bacteria.

What is the most appropriate initial treatment?

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A. Oral amoxicillin-clavulanate for 2 weeks and recheck, without drainage

Pus in the pleural cavity is a closed abscess: without evacuating it, the antibiotic penetrates poorly and the cat remains dyspnoeic and septic.

B. Immediate exploratory thoracotomy in every cat with pyothorax

In cats most respond to medical treatment with drainage; surgery is reserved for identifiable foci (lung abscess, foreign body), loculated effusion or lack of response.

C. Corticosteroids to reduce pleural inflammation and thoracocentesis if it worsens

Corticosteroids are contraindicated in an active bacterial infection and do not replace draining the pus.

D. Chest drains (often bilateral), pleural lavage with warm saline and intravenous antibiotics covering anaerobes and Pasteurella

Correct. In cats pyothorax is usually due to bite wounds, with mixed oral flora: Pasteurella and obligate anaerobes. Draining and lavaging removes pus and fibrin; an intravenous beta-lactam with a beta-lactamase inhibitor is a good basis, widening gram-negative cover if culture or severity requires it.

lightbulb Key takeaway

Always send fluid for aerobic and anaerobic culture before starting antibiotics, and adjust afterwards. Total antibiotic treatment usually lasts several weeks. Watch for sepsis: hypoglycaemia, hypothermia, bradycardia and effusion in other cavities worsen the prognosis.

References: ISCAID: guías de uso de antimicrobianos en enfermedad respiratoria del perro y el gato (2017)

What is the most appropriate initial treatment?

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