Objective:Auto-positive end-expiratory pressure (auto-PEEP) is a physiologic phenomenon defined as the positive alveolar pressure that exists at the end of expiration. Normally, the alveolar pressure is near zero at the end of expiration. However, certain ventilatory and/or physiologic paradigms can cause the development of auto-PEEP during cardiopulmonary resuscitation (CPR). Auto-PEEP has a detrimental cardiovascular effect similar to that of positive end-expiratory pressure that is intentionally applied to the ventilatory circuit in a mechanically ventilated patient. The connection between auto-PEEP and its cardiovascular effects, however, may go undetected. In this study, the effect that ventilatory factors have on auto-PEEP in a simulation of patients with lung disease undergoing CPR was delineated.Design:A case control study.Setting:Laboratory of a university hospital anesthesia department.Subjects:A baseline quantification of breathing patterns that occur during CPR was obtained by recording observed respiratory rate and relative tidal volume during treatment of in-hospital cardiac arrests.Measurements and Main Results:A test lung was set up to mimic a series of different airway resistances and lung compliances as would be seen in different types of pulmonary pathology. A sensitivity analysis was performed on each of the factors of respiratory rate, tidal volume, and inspiratory/expiratory ratio as to the effect each of these factors has on the development of auto-PEEP. Our study suggests that in various combinations of airway resistances and lung compliances, auto-PEEP can be generated to substantial levels depending on the methods of ventilation performed.Conclusion:We conclude from our findings that ventilation techniques during CPR may need to be altered to avoid the development of what may be a hemodynamically significant level of auto-PEEP.