The effect on intracuff pressure of various nitrous oxide concentrations used for inflating an endotracheal tube cuff

We sought to determine the optimal concentration of nitrous oxide (N2O) for inflating endotracheal tube cuffs, to avoid overinflation and air leaks. F emale patients undergoing endotracheal intubation (inner diameter 7.5 mm) d uring anesthesia with 67% N2O were randomly assigned to five groups of 25 s ubjects each, in which cuffs were inflated with 0% (Air), 30% (N30), 40% (N 40), 50% (N50), or 67% (N67) N2O. The cuff pressure and the N2O concentrati on in the cuff were measured. In an additional 15 patients (N40-a group), p ilot balloons were replaced with metal tubes, and the mouths and noses of t he patients were wrapped with tape, to minimize N2O efflux into the air. Po stoperative sore throats were evaluated in double-blinded interviews. Cuff pressures increased significantly in the Air and N30 groups but decreased i n the N67 group. Cuff pressures were <22 mm Hg in the N40 and N50 groups, b ut the N50 group had air leaks. The N2O concentration in the cuff in the N4 0 group was significantly smaller than that in the N40-a group, suggesting N2O rediffusion. The incidence of sore throats (40% in the Air group) was r educed significantly in the N40 and N50 groups. Therefore, 40% N2O is optim al for filling the cuff during anesthesia with 67% N2O.