Inadequate gas supply to patients with an adjustable pressure-limiting valve in the fully opened position.

With spontaneous ventilation, sufficient exhaust resistance at the adjustable pressure-limiting (APL) valve when fully opened ensures that the reservoir bag fills and adequately supplies gas to patients. A lack of exhaust resistance with the APL valve fully open caused inadequate gas supply to patients with four types of anesthesia machines: SA2 (Dräger), Excel-210 SE (GE), Fabius (Dräger), and Cato (Dräger). Mechanically, the SA2 and Excel-210 SE APL valve systems, which are of the spring-loaded disc type positioned horizontally, cannot maintain sufficient exhaust resistance with the APL valve fully open. As for the Fabius and Cato, an exhaust valve independent of the APL valve should maintain sufficient exhaust resistance continuously. However, accumulated viscous substances on the thin diaphragm of the exhaust valve contributed to hindrance of diaphragm closure.