Management of the feline pyothorax patient | VETgirl Veterinary Continuing Education Videos

In this VETgirl online veterinary continuing education video, we review pyothorax in a cat. Pyothorax is defined as the accumulation of septic purulent fluid within the pleural space, and can cause life-threatening respiratory distress and sepsis. When an exudative effusion begins to develop in the pleural space, secondary inflammatory changes occur that may worsen the effusion. Release of inflammatory cytokines and vasoactive mediators can affect capillary permeability and lymphatic flow, raise body temperature and cause endothelial damage, and thicken the pleura, preventing fluid resorption. Bacteria can enter the pleural space via damage anywhere along the respiratory tract (thoracic wall, trachea, bronchi, lung parenchyma) or via the esophagus. Pathogenic organisms can enter the thoracic cavity by trauma (e.g., bite wounds), vascular system (e.g., sepsis), infection from adjacent tissues, damage to the esophagus or trachea, etc. In cats, the most common isolates are Pasteurella and anaerobes.

In this video, a 5-year-old, male neutered, DSH, presented with fever, lethargy, weight loss, and tachypnea. This cat was an outdoor barn cat, often known to fight with other stray cats. On physical exam, the patient was febrile and had a shallow, rapid, dysynchronous respiratory pattern. Clinicopathologic testing revealed a negative FeLV/FIV status, increased globulins, and severe pleural effusion on radiographs. Thoracocentesis revealed a thick, viscous, opaque fluid, consistent with pus. Long filamentous bacteria were seen on cytology, and fluid analysis was submitted for culture.

The two main components of treatment for pyothorax are antimicrobial therapy and some type of thoracic drainage. Antibiotics should be broad-spectrum to start, with tailoring once culture and sensitivity results are available. Thoracic drainage is recommended in all cases of pyothorax to relieve the patient’s symptoms, minimize the potential for further procedures, remove as much infected fluid as possible and optimize imaging. Debate exists in human and veterinary medicine about medical versus surgical management of pyothorax. Either thoracostomy tube placement alone (for medical management) or surgical thoracic exploratory (typically via median sternotomy) can be performed. The benefit of surgical management of pyothorax is that it allows visualization of all the lung lobes (while also allowing chest tube placement). NOTE: Intermittent thoracocentesis is not recommended due to increased morbidity and risk. Chest tubes may be large bore (placed surgically) or small bore (placed via Seldinger technique) as both seem to be effective in draining fluid, and may be unilateral or bilateral depending on the distribution of fluid. Radiographs should always be performed following placement of chest tubes to ensure correct placement. There is no evidence to support flushing of the chest tubes, but possible benefits of lavage with warm saline include reduction of pleural fluid viscosity, facilitation of drainage, prevention of tube obstruction and dilution of bacteria. Little evidence exists to support intrapleural fibrinolytics or heparin.

In this patient, a single chest tube was placed for repeated thoracic lavage. To lavage the thoracic cavity, one should first remove as much pleural effusion as possible. Then, slowly instill 5-10 mL/kg warm sterile saline, gently roll the cat around, then suction back until negative pressure (VETgirl uses 20 ml/kg slowly). Note that all the instillate will not be obtained. This process can be continued several times a day initially, then tapered and used as needed. Chest tubes can be removed depending on clinical improvement, but can generally be considered when fluid production is less than 2 ml/kg/day, cytologic evidence of infection has resolved, and radiographs are improving. Complications of chest tubes include ascending infection, pain, clogging, or pneumothorax. Ultimately, the prognosis for cats with pyothorax is guarded, with about a 20% mortality rate. Generally, if cats survive beyond the first 2 days of treatment, they will typically have a good outcome. Owners should be warned of the prognosis and risk of recurrence (which is estimated to be approximately 15%).

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