Oxygen fail-safe device for an anaesthetic apparatus.

There are circumstances when the oxygen supply to an anaesthetic apparatus can fail. If this is not noticed immediately, the patient becomes anoxic. Many of the oxygen failure warning devices available at the present time only give a visual or audible signal of the failure and they rely on a second gas supply (usually nitrous oxide) and/or batteries for their operation (Falkner Hill, 1956; Hospital Equipment Information, 1965; Grogono. 1965; Wilson, 1965; Adler and Burn, 1967; Cooke and Waine, 1967; Ward, 196Sb). Recently others (Epstein et al., 1962; Lucas and Fisher, 1967; Ward, 1968a; Matteo, Gissen and Lee, 1969) have been described which not only signal the failure of the oxygen supply but also switch or cut off the supply of all other anaesthetic gases. These latter mechanisms go a long way to providing improved safety, but some hazards still remain.