A complication of mechanical ventilation in which the ventilator does not permit the patient sufficient time to exhale. This causes air to be trapped in the lungs, particularly the alveoli. If continued, auto-PEEP causes respiratory muscle fatigue and can cause rupture of the lung (i.e., pneumothorax). Auto-PEEP may be corrected by increasing exhalation time, decreasing the ventilator rate, or switching the ventilation mode so that the patient’s spontaneous respiratory pattern governs the inspiratory and expiratory times.