[Cuff pressure changes due to diffusion of nitrous oxide. A contribution to the question of the in vivo-diffusion--area of the cuff].

The mechanisms of nitrous oxide-diffusion through the endotracheal tube-cuff wall are still unknown in detail. In 30 patients we observed the pressure in low and high pressure-cuffs during operations with extracorporeal circulation (ECC). Under the chosen circumstances we found in low pressure-cuffs an increase of the initial pressure of 15.15 mm Hg up to 74,7 mm Hg until the beginning of ECC. During the ECC cuff pressure decreased to 32.25 mm Hg and was dependent on the body-temperature of the patients. After ECC the cuff pressure increased again up to 79.05 mm Hg until the operation was finished. The pressure changes in high pressure-cuffs were similar at different pressure-levels. These results show that in vivo the whole cuff-wall is diffusion-area for nitrous oxide. The main part of gas diffusion occurs through the contact area of the cuff with the tracheal wall.