We sought to determine the optimal concentration of nitrous oxide (N(2)O) for inflating endotracheal tube cuffs, to avoid overinflation and air leaks. Female patients undergoing endotracheal intubation (inner diameter 7.5 mm) during anesthesia with 67% N(2)O were randomly assigned to five groups of 25 subjects each, in which cuffs were inflated with 0% (Air), 30% (N30), 40% (N40), 50% (N50), or 67% (N67) N(2)O. The cuff pressure and the N(2)O concentration in the cuff were measured. In an additional 15 patients (N40-a group), pilot balloons were replaced with metal tubes, and the mouths and noses of the patients were wrapped with tape, to minimize N(2)O efflux into the air. Postoperative sore throats were evaluated in double-blinded interviews. Cuff pressures increased significantly in the Air and N30 groups but decreased in the N67 group. Cuff pressures were <22 mm Hg in the N40 and N50 groups, but the N50 group had air leaks. The N(2)O concentration in the cuff in the N40 group was significantly smaller than that in the N40-a group, suggesting N(2)O rediffusion. The incidence of sore throats (40% in the Air group) was reduced significantly in the N40 and N50 groups. Therefore, 40% N(2)O is optimal for filling the cuff during anesthesia with 67% N(2)O.
Implications: Nitrous oxide (N(2)O) diffuses into the cuff, equilibrating at a smaller concentration than the gas mixture with which patients are ventilated. Our data indicate that inflation of the cuff with 40% N(2)O is recommended to prevent both excessive endotracheal cuff pressure and air leaks during anesthesia with 67% N(2)O, reducing postoperative sore throats.