Lung Abscess

Definition: Severe localised suppuration of lung associated with cavity formation on CXR (often with a fluid level) and NOT due to TB.

Causes:

most common is aspiration following loss of consciousness due to anaesthetics, trauma, intoxication, illicit drugs, sedatives, or opioids
more common in patients with periodontal disease.

Suppurative thromboembolism
(eg, septic embolism from IV drug use)Right-sided endocarditis

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hematogenous seeding of the lungs

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necrotizing pneumonia

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Abscess(may result in multiple lung abscesses)

Pathogens:

most common: aspiration are anaerobic bacteria, but about half of all cases involve both anaerobic and aerobic organisms
most common aerobic: streptococci and staphylococci(sometimes MRSA)
other: Klebsiella pneumonia,Pseudomonas aeruginosa, Other streptococci
anaerobic: Bacteroides, Clostridium
Immunocompromised: Nocardia, Mycobacteria sp, or fungi(Aspergillus,Cryptococcus neoformans)
Developing countries: Mycobacterium tuberculosis

Noninfectious causes:

Pathology:

Introduction of these pathogens into the lungs 🡪 causes inflammation 🡪 tissue necrosis 🡪 abscess formation
abscess 🡪 ruptures into a bronchus🡪contents are expectorated 🡪 leaving an air- and fluid-filled cavity.
1/3 rd of cases🡪 direct or indirect extension (via bronchopleural fistula) 🡪 into the pleural cavity 🡪 empyema(presence of pus in the pleural space).
Erosion of the infection to a pulmonary artery 🡪 haemoptysis

Clinical Features:

Symptoms:

productive cough – sometimes blood-stained, foul-smelling (anaerobic); sudden expectoration if abscess ruptures into bronchus
pleuritic pain
swinging fever
systemic upset (fever, wt loss, malaise)

Signs:

crackles over the affected area

egophony + dullness to percussion 🡪 effusion.

Investigations for lung abscess

blood culture—if haematogenous spread from Staphylococcus aureus bacteraemia or septic jugular thrombophlebitis is suspected, or the patient has sepsis or septic shock, collect three sets of blood samples for culture before starting antibiotic therapy.
sputum Gram stain and culture—collect a sputum sample for Gram stain and culture before starting antibiotic therapy. Ensure a good quality sample (eg presence of polymorphs, but few or no squamous epithelial cells on microscopy) is collected.
pleural ultrasound—if loculated parapneumonic effusion is a differential diagnosis, perform a pleural ultrasound. This test is usually superior to computed tomography (CT) in determining loculation.
CT of the chest—if the diagnosis is uncertain, perform CT of the chest to distinguish between a peripheral lung abscess and empyema.
echocardiogram—if bacteraemia is suspected in an adult, perform a transthoracic echocardiogram (TTE) or transoesophageal echocardiogram (TOE) to exclude endocarditis
bronchoscopy—if an obstructing tumour or aspirated foreign body (eg tooth, peanut) is suspected, perform bronchoscopy. In immunocompromised patients, bronchoscopy may be indicated to obtain samples for extensive microbiological testing, because infection with unusual pathogens is possible

Management

Non-severe lung abscess + do not have systemic features of infection or chest wall pain:	amoxicillin 1 g (child: 25 mg/kg up to 1 g) PO/IV, TDS PLUS metronidazole 400 mg (child: 10 mg/kg up to 400 mg) PO/IV, BD
Non-severe lung abscess + systemic features of infection or chest wall pain, use:	benzylpenicillin 1.2 g (child: 50 mg/kg up to 1.2 g) IV QID PLUS metronidazole 400 mg (child: 10 mg/kg up to 400 mg) PO/IV, BD
Community-acquired severe lung abscess due to aspiration of oral bacteria	Amoxicillin Clavulanate IV 1+0.2g QID if septic shock, add gentamicin and vancomycin
Lung abscess due to Staphylococcus aureus	flucloxacillin 2 g (child: 50 mg/kg up to 2 g) IV QID PLUS vancomycin (adult and child) 25 to 30 mg/kg intravenously