Pre-anesthetic cimetidine and gastric pH.

Abstract

The effects of pre-anesthetic cimetidine on gastric fluid pH and volume were studied. Twenty-three patients scheduled for elective operation were randomized into two groups. Nasogastric tubes were placed and gastric fluid volume, pH, free acid, and total acid concentration measured the night before operation. Eleven patients received cimetidine, 300 mg IV, 2 hours before induction of anesthesia while the other 12 patients were given glycopyrrolate, 0.3 mg IM, 1 hour before induction of anesthesia. Gastric fluid volume, pH, free acid, and total acid concentration were determined hourly for 2 hours after cimetidine and 1 hour after glycopyrrolate before the induction of anesthesia. The results showed cimetidine to be statistically significantly superior after 1 hour (p < 0.05) and 2 hours (p < 0.001) compared to glycopyrrolate after 1 hour in increasing gastric fluid pH. Cimetidine increased the mean pH from 1.73 ± 0.07 (SE) to 4.43 ± 0.54 (p < 0.001) after 1 hour and to 7.23 ± 0.15 (p < 0.001) after 2 hours. Glycopyrrolate increased the pH from 1.59 ± 0.50 to 2.83 ± 0.49 (p c 0.025) after 1 hour. Total acid concentration decreased significantly in both groups. In those given cimetidine, the total acid concentration decreased 98% from 47.4 ± 4.5 mEq/L to 0.8 ± 0.79 mEq/L after 2 hours. This 98% decrease in total acid was significantly greater than the 5090 decrease observed 1 hour after glycopyrrolate (from 70 ± 4.6 mEq/L to 35 ± 5.7 mEq/L). Gastric fluid volume decreased in both groups. In patients given cimetidine, volume decreased from 69.9 ± 17.7 to 24 ± 7.2 ml, 2 hours after cimetidine. In patients given glycopyrrolate gastric volume declined from 76.4 ± 13.6 to 21.0 ± 2.7 ml 1 hour after glycopyrrolate. These findings demonstrate that cimetidine markedly increases gastric pH from an acid to a neutral range and also decreases gastric fluid volume in preoperative surgical patients.