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Incompetent expiratory valve: Signs

Any obstruction to outflow can potentially lead to increased airway pressure, reduced minute ventilation, lung hyperinflation, and subsequent cardiopulmonary effects (ex. hypotension due to decreased venous return, lung injury due to volutrauma/barotrauma). The capnograph may show a prolonged expiratory upstroke (similar to in COPD)

An expiratory valve stuck in the open position may be detected by failure of capnogram to return to zero.

Expiratory Valve Dysfunction

  • Stuck Closed: rise in airway pressures, reduced MV
  • Stuck Open: failure of capnogram to return to zero


  1. S T Pyles, L S Berman, J H Modell Expiratory valve dysfunction in a semiclosed circle anesthesia circuit–verification by analysis of carbon dioxide waveform. Anesth. Analg.: 1984, 63(5);536-7 PubMed Link