Modified occlusion tests for the Bain breathing system.

Undetected defects in the inner tube of the Bain coaxial anaesthetic breathing system may result in a greatly increased apparatus deadspace. Several authorities have advocated tests intended to detect inner tube problems; however, the efficacy of these tests has never been validated. In this study none of the tests were able to detect all the induced defects. A modification of an existing test using the backbar pressure-relief valve and a new double occlusion test were sufficiently sensitive to detect all defects.