An in vitro method to measure permeability of gases through a cuff membrane of tracheal tube in conditions relevant to its clinical uses.

The cuff pressure on a tracheal tube while being used in a clinical setting is affected by various physiological conditions. Hence, it is difficult to accurately assess the tracheal tube cuff membrane permeability for gases. We developed an experimental system that enabled accurate assessment of the transition and permeability of gases through a cuff membrane. To simulate nitrous oxide anesthesia, the partial pressure about a cuff membrane was considered separately in oral side, pulmonary side, and intracuff. The cuff pressure of a newly developed tracheal tube with gas barrier materials was assessed, and the permeability through the cuff membrane was evaluated. As a result, the study condition of Experiment II (the cuff was inflated with a gas mixture of 50% nitrous oxide and 50% oxygen) was the most appropriate in which the intracuff was inflated with the same gas mixure because of no concentration gradient between intra- and extra-cuff space. In the schematic diagram of the intracuff pressure changes during anesthesia with nitrous oxide, because of concentration gradient of the gas mixture, gases flow from pulmonary side into the cuff and in the latter phase gases pass through the cuff membrane. Our in vitro experimental system was revealed to be useful in accurately assessing the gas permeability through the cuff membrane of a tracheal tube in conditions relevant to clinical uses.