Positive end-expiratory pressure (PEEP) is a mode of therapy used in conjunction with mechanical ventilation. It is the pressure in the lungs above atmospheric pressure that exists at the end of expiration. PEEP is used to maintain the patients airway pressure above the atmospheric pressure at the end of mechanical or spontaneous exhalation. The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by an incomplete exhalation) . PEEP is a therapeutic parameter set in the ventilator (extrinsic PEEP), or a complication of mechanical ventilation with air trapping (auto-PEEP) .

PEEP is used to prevent the collapse of distal alveoli and to promote recruitment of collapsed alveoli. It can improve oxygenation by recruiting otherwise closed alveoli, thereby increasing the surface area for gas exchange. PEEP can also increase the compliance of the lung, which is the relationship between the change in volume and the change in pressure in the lung. With PEEP, less pressure is needed to get the same volume of air into the lung as the alveoli are already partially inflated and therefore do not need that high initial pressure to open them.

However, PEEP can cause some problems for patients who have airway obstruction, such as asthmatics and those with chronic obstructive pulmonary disease (COPD) . High PEEP can lead to barotrauma and a drop in cardiac output, so protocols should be in place to counter these complications. All healthcare professionals who look after ventilated patients should know the indications and potential adverse effects of PEEP. The ventilator settings should only be changed by one dedicated person, namely the respiratory therapist, and any time a change is made, it should be charted.