In patients receiving
mechanical ventilation there occasionally occurs an unintentional
positive end-expiratory pressure, known as
auto-PEEP, a phenomenon that can easily go undetected. Potential adverse effects of
auto-PEEP include misleading hemodynamic information, cardiopulmonary morbidity, or both. Our study was designed to evaluate the incidence of
auto-PEEP, its magnitude, and factors influencing it in a university hospital. Every patient receiving ventilation was evaluated for controlled ventilation and
auto-PEEP in medical and
surgical intensive care units during a 3-month period. Expiration was stopped at the instant that the next inspiration would have been delivered. At this moment, when the pressures in the lung and the
ventilator circuit had equilibrated, the level of
auto-PEEP was systematically measured. Of 57 patients undergoing controlled
mechanical ventilation, 27 (47%) had 1 to 6 cm H2O of
auto-PEEP. The incidence of
auto-PEEP increased significantly when the minute ventilation exceeded 18.4 L/min, the respiratory rate was higher than 27 breaths/min, or the set PEEP was greater than or equal to 10 cm H2O. Therefore,
auto-PEEP is the result of several
ventilator-related factors. Because
auto-PEEP occurred in 47% of the patients in the study, routine monitoring for
auto-PEEP in patients receiving controlled ventilation is recommended. Further studies of
auto-PEEP and its clinical impact are warranted.