COMPARISON OF TESTS FOR DETECTING LEAKS IN THE LOW-PRESSURE SYSTEM OFANESTHESIA GAS MACHINES

Small leaks in the low-pressure system (LPS) of the anesthesia gas mac hine can cause hypoxia or patient awareness. We sought to determine th e relative sensitivities of the various tests recommended for detectin g LPS leaks before anesthesia. Special adapters were fashioned to crea te leaks of six different sizes in the LPS that were equivalent to the following: a single 25-, 22-, 20-, or 15-gauge needle, two 15-gauge n eedles, or a 2.5-mm endotracheal tube connector. With each leak condit ion, five different leak tests were performed on three each of the fol lowing machines: Ohmeda Modulus I(TM), Ohmeda Modulus II(R)-Plus, and North American Drager Narkomed (2A, 3 and 4), for a total of 54 leaks to be detected for each leak test (3 x 3 x 6). The number of leaks det ected with each test was compared by Fisher's exact test P < 0.05 bein g considered significant. Only the negative pressure leak test detecte d all 54 leaks, a significant difference from the positive pressure te st, which detected the least number of leaks, 28 (P < 0.05). Some leak tests are more suitable for specific anesthesia machines. Adoption of the negative pressure test as a universal LPS leak test may prevent t he risks associated with using the wrong test for the particular anest hesia machine: hypoxic gas or patient awareness.