Unexpected intraoperative hypercapnia due to undetected expiratory valve dysfunction--a case report.

The normally functioning of anesthetic circle system depends mainly on the integrity of both inspiratory and expiratory unidirectional valves which keep the inspiratory gas will not be contaminated by the expired CO2. In case there is a leakage defect in one or both of these valves, i.e. inability to keep tightly closed during the cycle, retrograde gas flow may happen and the exhaled CO2 may get into the inspiratory limb, resulting in rebreathing and hypercapnia with disastrous aftermath. Here we report a rather rare incident of unrecognized expiratory valve insufficiency that was not detected before anesthesia in a 40-year-old female patient who developed intraoperative hypercapnea during general anesthesia with mechanical ventilation. Discussions on the causes, management, and prevention of hypercapnia due to respiratory valve dysfunction are presented.