Comparison of tests for detecting leaks in the low-pressure system of anesthesia gas machines

Small leaks in the low-pressure system (LPS) of the anesthesia gas machine can cause hypoxia or patient awareness. We sought to determine the relative sensitivities of the various tests recommended for detecting LPS leaks before anesthesia. Special adapters were fashioned to create 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 needles, or a 2.5-mm endotracheal tube connector. With each leak condition, five different leak tests were performed on three each of the following machines: Ohmeda Modulus I, Ohmeda Modulus II-Plus, and North American Dräger 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 detected with each test was compared by Fisher's exact test, P < 0.05 being considered significant. Only the negative pressure leak test detected all 54 leaks, a significant difference from the positive pressure test, 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 the risks associated with using the wrong test for the particular anesthesia machine: hypoxic gas or patient awareness.