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©2013 UpToDate ® Print Email Quantification of the auto-PEEP effect During mechanical ventilation of the patient with airflow obstruction, expiratory flow is too slow to allow complete deflation of the lung to its normal relaxed state before the ventilator delivers another breath. Slow flow continues until interrupted by the next inflation. Upper panel: Alveolar pressure remains positive at end exhalation (15 cmH2O) but is not measured by the ventilator manometer (0 cmH2O) located downstream from the site of increased airway resistance. Lower panel: Alveolar pressure at end-exhalation can be quantified by stopping flow transiently at the end of a set exhalation period, thereby allowing equilibration of pressures. Adapted from O'Quinn, R, Marini, JJ, Am Rev Respir Dis 1983; 128:319.