Positive end-expiratory pressure

Positive end-expiratory pressure (PEEP) is the pressure maintained in the lungs above atmospheric pressure at the end of expiration during mechanical ventilation. Clinicians apply extrinsic PEEP directly through the ventilator, commonly starting near 4 to 5 cmH2O to prevent alveolar collapse at the end of each breath, with higher levels used to improve oxygenation or reduce ventilator-associated lung injury in conditions such as acute respiratory distress syndrome. Intrinsic, or auto, PEEP instead develops unintentionally when a patient cannot fully exhale before the next breath begins, trapping air progressively, a risk with high respiratory rates or airway obstruction. Because raising lung pressure affects the chest and vessels together, PEEP can reduce cardiac output and blood pressure and carries a risk of barotrauma from overinflation, so clinicians balance its oxygenation benefit against these hemodynamic costs. The technique traces to English anaesthetist John Scott Inkster, who described it as Residual Positive Pressure in 1968.