Chest
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The purpose of this study is to describe an unexpected degree of differences between expiratory occlusion plateau pressure (EPO) and airway opening pressure (Pawo) measured level of intrinsic positive end-expiratory pressure above externally applied (auto-PEEP) that was found in six critically ill patients. In six patients (ten studies), the presence and degree of auto-PEEP found during the EPO maneuvers was not confirmed by Pawo measurements. ⋯ Because of the static nature of the EPO determination, a rise in pressure could conceivably be caused by the presence of subcutaneous or mediastinal emphysema and retrograde flow across the airway defect during exhalation. We suggest another cause for auto-PEEP-dynamic hyperinflation from extrapulmonary flow limitation.