Sore throat after intubation of the trachea

Eighty female patients were allocated randomly to groups, divided in three ways, to investigate the effects of using cuffed p.v.c. v. red rubber tracheal tubes, intermittent adjustment of the cuff volume, and humidification of inspired gases on the incidence and severity of sore throat after tracheal intubation. In addition, the influence of the anaesthetist's participation in the trial was studied by assessing sore throat in a further 60 female patients where the anaesthetists were unaware of the trial. There were no significant differences between any of the groups despite using three sensitive methods of assessment. In terms of the simple discrimination between "sore throat" and "no sore throat" the 95% confidence limits of the differences of incidence were generally +/- 15-20%. If there are any real differences produced by these changes, and if any of them were as large as 15% then, to show with 95% confidence that any difference is at least 10%, would require a trial involving about 1400 patients. Retrospective analysis of the results showed no difference between patients who received suxamethonium and those who did not.