[Anesthesia machine malfunction caused by the blockade of an exhaust gas port].

We report an intraoperative case of anesthesia machine (ACOMA ANESPIRATOR KMA-1300III, ACOMA Medical Industry Co., Ltd., Tokyo) malfunction. The ventilator, which had run normally on the preanesthetic inspection, suddenly went out of order showing the negative circuit pressure. This accident was caused by the obstruction of the exhaust gas port with a vinyl bag, resulting in the failure in expansion of ventilator bellows. While minute volume exceeds fresh gas flow, the bellows are replenished with gases from the exhaust gas pocket connected to both the exhaust gas port and the excess gas aspirator. Mannual ventilation could be properly carried out. Our incident led the manufacturer to provide a safety device and to issue the notice of trouble.