Cimetidine as a prophylactic against acid aspiration at tracheal extubation.

Gastric acidity was studied immediately after induction of balanced anaesthesia and again just before extubation of the trachea in 76 elective surgical patients. In 26 patients who were not given cimetidine before operation, the mean gastric [H+] at intubation was 2.6 x 10(-2) +/- 2.3 x 10(-2) mEq/l (pH 2.02 +/- 0.22) and was more than 3.16 x 10(-3) mEq/l (pH less than 2.5) in 53 per cent at extubation (mean [H+] 3.0 x 10(-2) +/- 2.2 x 10(-2) mEq/l; pH 1.83 +/- 0.22). In contrast, of those premedicated with intravenous cimetidine 45 minutes before tracheal intubation, none had a gastric [H+] more than 3.16 x 10(-3) mEq/l (pH less than 2.5) irrespective of the duration of the operation (15-180 minutes). However, of those patients receiving cimetidine 15 minutes before intubation, one-third failed to achieve a gastric [H+] less than 3.16 +/- 10(-3) mEq/l (pH greater than 2.5) at the time of extubation. Properly timed premedication with intravenous cimetidine will reduce the risk of acid-related pulmonary damage if aspiration occurs at the time of intubation or extubation. Repeated administration should be considered when the interval between premedication and extubation exceeds four hours.