Negative Pressure Pulmonary Oedema

Negative pressure pulmonary oedema (NPPE) is non-cardiogenic pulmonary oedema after forceful inspiration against an obstructed upper airway, most often laryngospasm.

Epidemiology. It affects about 0.05% to 0.1% of anaesthetics, mostly in young, fit, muscular men. Type 1 follows acute obstruction (laryngospasm, biting the tube, tumour). Type 2 follows relief of chronic obstruction (tonsillectomy, upper airway tumour excision).

Pathophysiology.

Forced inspiration against a closed glottis creates intrathoracic pressure down to minus 50 to minus 100 cmH2O. This raises venous return and left ventricular afterload, increases transcapillary hydrostatic gradient, and with hypoxia damages the alveolar capillary membrane.

Hypoxia, catecholamine surge and shift of blood to the lungs add to leakage.

Desaturation, frothy pink sputum, bilateral crackles, respiratory distress, tachypnoea and tachycardia, usually within minutes of relief of obstruction (delay up to 6 hours is described).

Red flags.

• Saturation under 90% despite oxygen.
• Haemoptysis.
• Hypotension or arrhythmia.

Clinical, with chest radiograph showing bilateral alveolar infiltrates and normal heart size. Echocardiography excludes cardiac failure. Blood gas shows hypoxaemia. Rapid resolution within 12 to 48 hours supports the diagnosis.

Differential diagnosis.

• Aspiration.
• Cardiogenic pulmonary oedema.
• Fluid overload.
• Anaphylaxis.
• Pulmonary embolism.
• Transfusion related lung injury.

Relieve the obstruction, give 100% oxygen and apply continuous positive airway pressure of 5 to 10 cmH2O. Intubate and ventilate with positive end expiratory pressure of 5 to 10 cmH2O (lung protective tidal volume 6 to 8 mL/kg ideal weight) if hypoxaemia persists.

• Furosemide: 20 to 40 mg IV once, repeated after 1 to 2 hours if volume overloaded; maximum 80 mg for this indication; monitor urine output, potassium and blood pressure; avoid in hypovolaemia (the usual state in NPPE) and reduce in renal impairment.

Diuretics are not routinely needed because patients are usually euvolaemic. Steroids have no proven benefit.

Prevention. Place a bite block before emergence and treat laryngospasm quickly.

Monitoring. Saturation, chest radiograph, blood gas and fluid balance for 12 to 24 hours.

Referral and escalation. Critical care for ventilatory support. Most cases resolve in 24 to 48 hours.