Lung abscess and aspiration pneumonia in ICU

Also known as Lung abscess · Pulmonary abscess · Aspiration pneumonia · Necrotising pneumonia · Empyema · Mendelson syndrome

Lung abscess: localised collection of pus in lung parenchyma (cavity with air-fluid level). Primary abscess arises from aspiration of oropharyngeal contents (anaerobes, S. milleri) in a host with impaired consciousness or swallow — alcoholism, seizure, stroke, poor dentition. Secondary abscess follows bacteraemic seeding — right-sided endocarditis (S. aureus in IVDU), septic thrombophlebitis (Lemierre, Fusobacterium), infected lines — or bronchial obstruction (cancer, foreign body). Necrotising pneumonia is a severe, confluent tissue-destructive process (PVL-producing S. aureus, Klebsiella, type 3 pneumococcus). Aspiration PNEUMONIA (bacterial infection after macro-aspiration, 24-48 h onset, dependent segments, anaerobes) is distinct from aspiration PNEUMONITIS (Mendelson syndrome — sterile chemical injury from acidic gastric contents, onset within hours, no routine antibiotics). Treatment: prolonged antibiotics typically 3-6 weeks (clindamycin or amoxycillin/clavulanate for aspiration; organism-directed for necrotising), percutaneous drainage for large or non-responding abscesses, surgical resection for failure or massive haemoptysis, and treatment of the underlying cause plus an aspiration prevention bundle.

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8 MCQs

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Lung abscess: cavity with air-fluid level in lung parenchyma. Primary — aspiration (anaerobes, S. milleri) in impaired consciousness/swallow; secondary — bacteraemic (right-sided endocarditis, Lemierre, infected line) or bronchial obstruction (cancer, foreign body). Aspiration pneumonia: bacterial infection 24-48 h after macro-aspiration (altered consciousness, dysphagia) — different from aspiration pneumonitis (Mendelson): sterile chemical injury from acidic gastric contents, onset within hours, no routine antibiotics. Treatment: prolonged antibiotics — typically 3-6 weeks (clindamycin or amoxycillin/clavulanate for aspiration; organism-directed for necrotising), percutaneous/surgical drainage if the abscess is large, non-responding or complicated, treat the underlying ca…

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Management of lung abscess

Recognise — fever, cough, foul-smelling sputum, weight loss. Chest X-ray/CT: cavity with air-fluid level, thick wall
Identify cause — aspiration (alcoholism, seizure, stroke), necrotising pneumonia (S. aureus, Klebsiella), septic emboli (endocarditis — examine for murmur, IVDU), bronchial obstruction (cancer, foreign body), immunocompromise
Antibiotics (prolonged) — IV initially, then oral. Aspiration/anaerobic: clindamycin OR amoxycillin/clavulanate (clindamycin outperformed penicillin in the classic RCT). Necrotising: cover specific organism (flucloxacillin/vancomycin for S. aureus). Duration: typically 3-6 weeks (until cavity resolves or stable) — median 38 days in a contemporary cohort
Source control — percutaneous drainage (large abscess, no response to antibiotics, deterioration, or coexisting empyema). Surgical resection (if drainage fails, massive haemoptysis, malignancy)
Treat underlying cause — dental hygiene (aspiration), alcohol rehabilitation, seizure control, stroke rehabilitation, endocarditis treatment, relief of obstruction
Nutrition — these patients are often malnourished (alcoholism, chronic illness). Enteral nutrition, thiamine and B vitamins in alcohol use disorder
Follow-up — repeat imaging (ensure cavity resolving). Bronchoscopy if not resolving (exclude malignancy, foreign body, obstruction)

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SAQ — Cavitating lung lesion in a chronic alcoholic

10 minutes · 10 marks

A 58-year-old man with chronic alcohol use disorder is admitted from the ED with a two-week history of productive cough, fever, 8 kg weight loss and foul-smelling sputum. He has poor dentition. Chest X-ray shows a 5 cm cavitating lesion with an air-fluid level in the posterior segment of the right upper lobe. CRP 240, WCC 18.4,Albumin 28.

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SAQ — Aspiration pneumonia versus aspiration pneumonitis (Mendelson syndrome)

10 minutes · 10 marks

A 72-year-old man is admitted to ICU three hours after a large witnessed aspiration of gastric contents during a generalised tonic-clonic seizure. He has a residual dense right hemiparesis from an ischaemic stroke four months ago. He is tachypnoeic, SpO2 88 per cent on room air, diffusely wheezy with crackles in the right lower lobe. CXR shows new bilateral basal infiltrates.

Clinical pearls

High-yield lung abscess / aspiration pneumonia points for CICM/FFICM exam

Aspiration is the #1 cause of lung abscess. Risk factors: ALCOHOLISM (most common), seizure disorder, stroke (dysphagia), altered consciousness (sedation, anaesthesia, drug overdose), oesophageal disease (achalasia, strictures, Zenker's diverticulum), poor dental hygiene. The aspirate is ORAL FLORA — anaerobes (Peptostreptococcus, Prevotella, Fusobacterium) and streptococci (S. milleri group).^[2]
Foul-smelling (putrid) sputum = anaerobic infection. Anaerobes produce volatile fatty acids → putrid odour. If sputum smells foul → anaerobes (aspiration). Do not waste time on anaerobic culture of expectorated sputum (contaminated by oral flora, slow, fastidious) — start empiric anaerobic cover (clindamycin or amox-clav) and rely on aspirate/BAL if needed.^[1]^[23]
Cavity with air-fluid level on imaging = lung abscess. Chest X-ray: round opacity with an air-fluid level (only if the cavity communicates with a bronchus). CT (definitive): thick-walled cavity, air-fluid level, surrounding consolidation. LOCATION follows gravity: dependent segments — posterior segment of the UPPER lobe and superior segment of the LOWER lobe (aspiration in the supine patient); basal lower lobe (aspiration in the upright patient).^[3]
Necrotising pneumonia — aggressive organisms. S. aureus producing Panton-Valentine leucocidin (PVL), Klebsiella pneumoniae (especially hypervirulent capsular serotype K1/K2 in East Asia), type 3 S. pneumoniae, Pseudomonas, and group A streptococcus. Causes RAPID tissue necrosis, cavitation, multi-focal abscesses and often an empyema. High mortality — needs aggressive antibiotics plus source control.^[4]
Antibiotics for aspiration pneumonia/abscess: clindamycin OR amoxycillin/clavulanate. Cover anaerobes + streptococci. In the classic randomised trial, clindamycin beat penicillin for anaerobic lung abscess — shorter febrile period (4.4 vs 7.6 days), fewer days of fetid sputum, no treatment failures or relapses, and cure in all 13 evaluable clindamycin patients vs 8 of 15 on penicillin. Duration: typically 3-6 weeks for abscess (no relapse with clindamycin given for 3 or 6 weeks; median 38 days in a contemporary Danish cohort) — substantially longer than for uncomplicated pneumonia.^[23]^[24]
Percutaneous drainage for large or non-responding abscess. Image-guided (CT or ultrasound) catheter drainage. Indications: a large abscess, no clinical/radiographic response to an adequate antibiotic course, clinical deterioration, or coexisting empyema. Avoid if the abscess is adjacent to major vessels (bleeding risk) or if the route crosses uninvolved lung (risk of bronchopleural fistula). Surgical resection if drainage fails or for massive haemoptysis.^[14]
Aspiration PNEUMONITIS vs PNEUMONIA — different conditions. PNEUMONITIS (Mendelson syndrome): chemical injury from acidic gastric aspiration (pH < 2.5) — sterile, acute onset within hours, NO antibiotics initially (unless infection develops over 48-72 h). PNEUMONIA: bacterial infection 24-48 h after macro-aspiration — needs antibiotics covering aerobes + anaerobes. If macro-aspiration occurs, observe for infection and treat only if fever, rising WCC, purulent sputum, or progressive infiltrates appear.^[5]
Prevention of aspiration in ICU. Head-of-bed elevation 30-45°, avoid unnecessary sedation, good oral hygiene (chlorhexidine / toothbrushing reduces oropharyngeal bacterial load), formal swallow assessment post-extubation, decompress the stomach (NGT), and use a subglottic suction ETT in the ventilated patient (reduces micro-aspiration around the cuff).^[22]
Septic emboli cause multiple peripheral abscesses. Sources: right-sided endocarditis (IVDU — S. aureus), septic thrombophlebitis of the internal jugular vein (Lemierre's syndrome — Fusobacterium necrophorum), and infected central venous catheters. Imaging: multiple peripheral nodules/cavities ("cannonball" lesions) with a feeding vessel sign. Treatment: treat the source (endocarditis, line removal), organism-directed antibiotics, and anticoagulation only if Lemierre with thrombosis.^[16]
Empyema — complication of pneumonia/abscess. Pus in the pleural space; suspect it with purulent fluid or a loculated effusion with a low pH and glucose and high LDH. Treatment: chest drain (large bore), intrapleural tPA/DNase if loculated, and VATS (video-assisted thoracoscopic surgery) for failure or multi-loculated collections. Streptokinase alone is NOT effective. Untreated, may progress to fibrothorax requiring surgical decortication.^[12]^[13]
Lung abscess vs cavitating lung cancer. Squamous cell carcinoma (primary) and squamous metastases (head and neck, cervix) can cavitate. Clues to malignancy: older smoker, weight loss, a thick, irregular cavity wall, eccentric or nodular inner wall, no surrounding consolidation, no air-fluid level (classically). Bronchoscopy with biopsy if suspicious — always consider malignancy in a cavitating lesion, especially one not responding to antibiotics.^[3]
Aspiration in stroke — dysphagia. Stroke (especially brainstem or large MCA territory) → dysphagia → aspiration. Assess swallow BEFORE oral intake (formal bedside swallow screen within 24 h). If dysphagic: NPO, NG or PEG feeding, speech-language therapy. A formal dysphagia screening protocol reduces post-stroke pneumonia.^[9]
Duration of antibiotics — typically 3-6 weeks. Lung abscess requires PROLONGED antibiotics (unlike uncomplicated pneumonia). Continue until: cavity resolves on imaging, OR cavity is stable and the patient is clinically well (a small stable residual cavity is acceptable). Contemporary cohorts report a median of 38 days (IQR 30-51); a Japanese series used a mean of 26 days, with Actinomyces and Nocardia infections needing months (76-189 days).^[24]^[3]
Bronchoscopy if not resolving. If a lung abscess is not improving despite an adequate course of appropriate antibiotics → bronchoscopy to: exclude obstruction (foreign body, tumour), obtain microbiology (BAL, protected specimen brush), and rarely to drain. A persistent cavity despite treatment prompts investigation for antibiotic resistance, undrained collection, an underlying lesion (cancer, foreign body), or immunodeficiency.^[3]

References25Show

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