Changes in Intracuff Gas Volune, Pressure and Gas Conponent with Nitrous Oxide Anaesthesia

To clarify the characteristics of endotracheal cuffs made of polyvinyl chloride (PVC),latex rubber (LR), and silicone rubber (SR), we made a comparative study on the change of intracuff pressure as well as on intracuff gas volume, gas component, and
gas concentration in nitrous oxide. These changes were measured in a plastic bag filled with nitrous oxide. Nitrous oxide diffused into all cuffs in a concentration and time-related fashion. The rates of nitrous oxide diffusion in SR cuffs were　considerable compared with those in LR and PVC cuffs. SR cuffs were also more permeable to oxygen and nitrogen than LR and PVC cuffs. Gas volume in SR cuffs rapidly increased within a short time and then decreased, though intracuff pressures did not change from the control values. On the other hand, gas volume and intracuff pressure in LR and PVC cuffs increased continuously with time. These findings suggest that the overexpansion of SR cuffs may cause tracheal obstruction and the high lateral pressure of PVC and LR cuffs may induce damage in the tracheal wall.