Spontaneous Bacterial Empyema

Spontaneous bacterial empyema is infection of a hepatic hydrothorax (pleural effusion in cirrhosis) without pneumonia. It is the pleural counterpart of spontaneous bacterial peritonitis.

It affects 10% to 15% of patients with hepatic hydrothorax, which itself occurs in about 5% to 10% of patients with cirrhosis and ascites. Right sided effusions predominate (about 85%). Mortality is about 20% in hospital.

Diagnosis needs a pleural fluid neutrophil count of 250 cells/mm3 or more with a positive culture, or 500 cells/mm3 or more with a negative culture, and no pneumonia. Organisms are mostly Gram negative enteric bacteria (Escherichia coli, Klebsiella) and Streptococcus and Enterococcus.

Pathophysiology.

Ascitic fluid passes through diaphragmatic defects into the pleural space, and bacterial translocation from the gut seeds the fluid. Low opsonic activity in cirrhotic effusion fluid allows infection.

Fever, pleuritic chest pain, dyspnoea, cough, abdominal pain, worsening encephalopathy, acute kidney injury and sepsis. About a third have no symptoms. Spontaneous bacterial peritonitis coexists in about 40%.

Red flags.

• Hypotension or sepsis.
• New acute kidney injury.
• Worsening encephalopathy.
• Respiratory failure.

Diagnostic thoracentesis with pleural fluid cell count and differential, culture (inoculate blood culture bottles at the bedside), protein, lactate dehydrogenase, glucose and pH. Perform diagnostic paracentesis to exclude peritonitis. Chest radiograph or CT excludes pneumonia and parapneumonic effusion. Blood cultures, creatinine and liver tests are sent.

Differential diagnosis.

• Parapneumonic effusion or empyema.
• Tuberculous pleuritis.
• Malignant effusion.
• Uninfected hepatic hydrothorax.
• Pulmonary embolism.
• Heart failure effusion.

Start antibiotics promptly, without waiting for culture. Avoid chest tube drainage unless the fluid is frankly purulent, because tube placement carries high rates of complications, protein loss and persistent leak.

• Ceftriaxone: 2 g IV once daily; 5 to 7 days (extend to 14 days if slow response); maximum 4 g daily; monitor culture, renal function and response with repeat thoracentesis at 48 hours; no dose reduction in renal impairment, and reduce to 2 g daily maximum in combined severe renal and hepatic impairment.
• Cefotaxime (alternative): 2 g IV every 8 hours for 5 to 7 days; maximum 12 g daily; monitor renal function; reduce the dose when creatinine clearance is under 10 mL/min.
• Albumin 20%: 1.5 g/kg IV on day 1 (maximum 100 g) and 1 g/kg on day 3 (maximum 100 g) when creatinine is over 90 micromol/L, urea over 11 mmol/L or bilirubin over 68 micromol/L; monitor for pulmonary oedema, and stop when the patient is fluid overloaded; extrapolated from peritonitis, so the evidence in empyema is limited.

Stop diuretics and non-selective beta blockers during hypotension or acute kidney injury. Tailor antibiotics to culture and local resistance. Refer for liver transplant assessment and consider a transjugular intrahepatic portosystemic shunt in refractory hydrothorax.

Secondary prophylaxis.

• Ciprofloxacin: 500 mg orally once daily; long term while hydrothorax persists; maximum 500 mg daily; monitor QTc, tendon pain and Clostridioides difficile; reduce to 250 mg daily when creatinine clearance is under 30 mL/min.

Monitoring. Temperature, renal function and pleural fluid neutrophil counts at 48 hours.

Referral and escalation. Hepatology and respiratory medicine; critical care for sepsis; transplant centre.