單向閥失能導致手術中高二氧化碳意外之病例報告

Unexpected Intraoperative Hypercapnia due to Undetected Expiratory Valve Dysfunction-- A Case Report

單向閥在閉鎖式或半閉鎖式呼吸迴路中，須確保病人呼出之氣體必定經過soda lime後才與新鮮氣體混合，然後再被病人吸入，才能保障病人吸入之氣體絕不含二氧化碳。若單向閥關閉不良，將導致雙向氣流，於是病人呼出之含二氧化碳氣體將被病人重新吸入，造成有致命危險的高二氧化碳現象。一40歲婦女在全身麻醉下接受闌尾切除手術時，因吐氣閥關閉不良而引發高二氧化碳。我們在此討論相關的成因，處置及預防方法。

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.