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©2013 UpToDate ® Print Email Trigger threshold for auto-PEEP Effect of auto-PEEP on elevation of the triggering threshold in a mechanically ventilated patient with obstructive airways disease. This graphic representation shows airway pressure over time; the solid blue line demonstrates the circuit pressure as measured by the ventilator manometer, and the dashed red line is the alveolar pressure. In the absence of auto-PEEP, the sensitivity setting of -1 cm H 2 O would be achieved by the patient making inspiratory efforts at the end of expiration, when airway pressure is at its minimum. In the presence of auto-PEEP, alveolar pressure remains positive. In this setting, the patient's inspiratory effort needs to decrease airway pressure not only by the -1 cm H 2 O sensitivity set on the machine, but also by the amount of positive alveolar pressure (auto-PEEP). In this graph, the patient's inspiratory efforts are insufficient to trigger the ventilator and the patient is "locked out," being unable to get a breath because of an inability to overcome the elevated effective triggering threshold rendered by auto-PEEP. PEEP: positive end-expiratory pressure. Adapted from Puritan-Bennett 1994, Form AA-1888.