Postoperative Pneumonia

Postoperative pneumonia is lung infection arising within 30 days of surgery, mostly in the first 5 to 7 days. It is hospital acquired (onset over 48 hours after admission) or follows aspiration.

Epidemiology. It occurs in about 1% to 5% of noncardiac surgery and 10% to 20% after upper abdominal, thoracic, oesophageal and aortic surgery. Mortality is about 20% to 30%.

Causes. Gram negative bacilli (Klebsiella, Escherichia coli, Enterobacter, Pseudomonas), Staphylococcus aureus including meticillin resistant strains, Streptococcus pneumoniae, Haemophilus influenzae, oral anaerobes in aspiration, and rarely Legionella.

Risk factors. Age over 65, COPD, smoking, albumin under 35 g/L, heart failure, functional dependence, long or emergency surgery, nasogastric tube, dysphagia, reflux, reintubation, prolonged ventilation and residual neuromuscular block.

Pathophysiology.

Impaired cough, atelectasis, microaspiration and mucociliary dysfunction allow colonising organisms to reach the lower airway.

Postoperative immune suppression and pain related splinting favour infection.

Fever over 38.0 C, new or worse cough, purulent sputum, dyspnoea, pleuritic pain, tachypnoea, hypoxaemia, crackles, bronchial breathing, confusion, and leucocytosis or leucopenia.

Red flags.

• Sepsis or shock.
• Saturation under 90% on oxygen.
• Respiratory rate over 30/min.
• Delirium.
• Empyema signs with persisting fever and pleuritic pain.

Diagnosis needs a new or progressive infiltrate on imaging plus at least two of: fever, white cell count over 12 or under 4 x 10^9/L, purulent secretions, and hypoxaemia.

Investigations.

• Blood cultures (2 sets) before antibiotics.
• Sputum or endotracheal aspirate culture.
• Full blood count, C-reactive protein, procalcitonin as an adjunct, lactate, urea, creatinine, blood gas.
• MRSA nasal screen.
• Legionella and pneumococcal urinary antigens when indicated.
• Pleural ultrasound and CT for effusion or complicated disease.

Differential diagnosis.

• Atelectasis.
• Cardiogenic pulmonary oedema.
• Pulmonary embolism.
• Acute respiratory distress syndrome.
• Aspiration pneumonitis (chemical, usually without need for antibiotics unless it persists beyond 48 hours).
• Pleural effusion.
• Transfusion related lung injury.

Supportive. Oxygen to saturation 94% to 98% (88% to 92% if hypercapnic risk), fluids, analgesia, chest physiotherapy, mobilisation, swallow assessment, venous thromboembolism prophylaxis, and CPAP or non-invasive ventilation for hypoxaemic or hypercapnic failure.

Antibiotics. Start within 1 hour if septic or in shock, otherwise within 4 hours, then narrow at 48 to 72 hours using culture results. Usual duration is 7 days if the response is good.

• Piperacillin-tazobactam: 4.5 g IV every 6 hours (extended infusion over 4 hours is acceptable); duration 7 days; maximum 18 g daily; monitor creatinine, full blood count and sodium; for creatinine clearance 20 to 40 mL/min give 3.375 g every 6 hours, under 20 mL/min give 2.25 g every 6 hours.
• Cefepime (alternative): 2 g IV every 8 hours; duration 7 days; maximum 6 g daily; monitor for neurotoxicity; for creatinine clearance 30 to 60 mL/min give 2 g every 12 hours, 11 to 29 mL/min give 2 g every 24 hours, under 11 mL/min give 1 g every 24 hours.
• Meropenem (resistant organisms): 1 g IV every 8 hours; duration 7 days; maximum 3 g daily; monitor seizures and creatinine; for creatinine clearance 26 to 50 mL/min give 1 g every 12 hours, 10 to 25 mL/min give 500 mg every 12 hours, under 10 mL/min give 500 mg every 24 hours.
• MRSA cover, vancomycin: 25 to 30 mg/kg IV loading dose, then 15 to 20 mg/kg every 8 to 12 hours; continue for the course; monitor levels (area under the curve 400 to 600) and creatinine; extend the interval in renal impairment. Alternatively linezolid 600 mg IV or orally every 12 hours; maximum 1200 mg daily; monitor platelets and avoid serotonergic drugs.
• Severe immediate penicillin allergy: aztreonam 2 g IV every 8 hours plus an MRSA agent; for creatinine clearance 10 to 30 mL/min halve the dose, under 10 mL/min give a quarter.

Complications. Drain empyema or complicated effusion. Intubate for refractory hypoxaemia, exhaustion or airway failure.

Monitoring. Temperature, saturation, respiratory rate, white cell count, C-reactive protein, creatinine and drug levels. Repeat imaging at 72 hours if no response.

Referral and escalation. Critical care if non-invasive ventilation, vasopressors, respiratory rate over 30/min or PaO2/FiO2 under 250 are present. Respiratory or thoracic surgical review for empyema or abscess.