AKT · Respiratory/Respiratory infectionlow yield

Empyema & lung abscess

Pus in the pleural space (empyema) / a localised cavity of pus in the lung (abscess)

Overview

Suppurative complications of chest infection. Empyema is pus in the pleural space (a complicated parapneumonic effusion), suspected when a patient with pneumonia has persistent/swinging fever; pleural fluid that is purulent, pH <7.2, low glucose or organism-positive needs a chest DRAIN. Lung abscess is a localised cavity of pus (air-fluid level on imaging) from aspiration, obstruction or necrotising infection, treated with prolonged antibiotics ± drainage.

Recognise

Empyema: ongoing/swinging fever and raised inflammatory markers in a patient with pneumonia/effusion, pleuritic pain, breathlessness; loculated effusion on imaging
Lung abscess: swinging fever, productive cough of foul/purulent sputum, weight loss, clubbing; CXR/CT shows a cavity with an AIR-FLUID LEVEL
Risk factors: aspiration (alcohol, reduced consciousness, poor dentition), bronchial obstruction (tumour), necrotising pneumonia (Staph, Klebsiella)

Red flags

Empyema (pleural fluid pH <7.2 / pus / low glucose / organisms) → CHEST DRAIN — antibiotics alone won't clear it
Lung abscess from bronchial obstruction → exclude an underlying tumour (bronchoscopy/CT)

Differentials & how to tell them apart

Uncomplicated parapneumonic effusionpleural fluid pH >7.2, not purulent — may resolve with antibiotics alone (no drain)

Cavitating lung cancer / TBcavity with weight loss/haemoptysis — CT/bronchoscopy/sputum AFB

Malignant effusionexudate with malignant cytology

Investigations

CXR/CT chest (loculated effusion → empyema; cavity with air-fluid level → abscess); PLEURAL ASPIRATION for empyema (pH <7.2, low glucose, pus, microscopy/culture); blood cultures, inflammatory markers; bronchoscopy if obstruction/tumour suspected.

Management

Empyema → chest drain + antibiotics; lung abscess → prolonged (anaerobic-cover) antibiotics ± drainage

1Suspect a complication when pneumonia doesn't settle (persistent/swinging fever). Image (CT) and ASPIRATE a parapneumonic effusion: empyema (pus, pH <7.2, low glucose, organisms) → CHEST DRAIN plus antibiotics.Gate: Pleural fluid pH <7.2 / pus / low glucose defines an empyema needing drainage — antibiotics alone are insufficient; a lung abscess from obstruction needs an underlying tumour excluded.
2Lung abscess → prolonged antibiotics with anaerobic cover ± drainage; treat aspiration risk; surgery (VATS/decortication) for empyema not resolving with drainage.

Empyema: CHEST DRAIN + prolonged antibiotics — intercostal drainage is essential; antibiotics cover the likely organisms (incl. anaerobes); surgery (VATS/decortication) if not resolving

Lung abscess: prolonged antibiotics (often weeks, anaerobic cover) — covers aspiration/anaerobic organisms; postural drainage/physiotherapy

Drainage for a large/non-resolving abscess — percutaneous or bronchoscopic; surgery rarely

Treat the cause — address aspiration risk; exclude/treat an obstructing tumour

Key points

Pneumonia + persistent/swinging fever → think empyema: aspirate — pus / pH <7.2 / low glucose = empyema → CHEST DRAIN (not antibiotics alone). Cavity + air-fluid level + foul sputum = lung abscess → prolonged anaerobic-cover antibiotics ± drainage; exclude an obstructing tumour.

Monitor & prognosis

Fever/inflammatory markers, drain output, imaging resolution; bronchoscopy if obstruction.

Good with timely drainage/antibiotics; delayed empyema needs surgery.

Source: BTS pleural disease; NICE