Detecting unidirectional valve incompetence by the modified pressure decline method.

The 1993 Food and Drug Administration anesthesia apparatus checkout recommendation provides guidance for a standardized circle system checkout but, we believe, inadequately tests unidirectional valve (UDV) function. We developed the modified pressure decline method (MPDM) for checking UDVs. The test involves pressurizing reservoir bags downstream of the UDVs to check for competency. Thirty-six UDVs in 18 anesthesia circle systems were evaluated using the MPDM. One Draeger (Draeger Medical Inc., Telford, PA) and one Ohmeda (Datex-Ohmeda Inc., Madison, WI) machine were then retested using incompetent valve discs. One incompetent UDV (3%) was identified of the 36 valves tested in 18 anesthesia machines. The MPDM detected the valve leak (Draeger 0.6 L/min flow leak; Ohmeda 0.9 L/min flow leak) when the incompetent valve discs were intentionally introduced into each type of machine. MPDM provides a quick and effective way of identifying incompetent UDVs.