Effects of single-dose oral ranitidine and sodium citrate on gastric pH during and after general anaesthesia

Abstract

The effects on gastric pH of the H2-receptor antagonist ranitidine (R) with 0.3 molar (M) sodium citrate (SC) as an oral effervescent and those of plain SC were studied in 25 patients scheduled for elective surgery. Following induction of general anaesthesia, the gastric contents were evacuated via a nasogastric tube, and a pH electrode was placed in the stomach. Then, eight patients received R 300 mg plus SC dose (Group R300), ten received R 150 mg plus SC dose (Group R150), and seven received 50 ml SC alone (Group SC). The drugs were administered orally in a double-blind fashion, and the gastric pH was recorded continuously over a period of 24 hr. Mean (range) baseline pH values were 1.2 (0.8-1.8), 1.3 (1.0-1.8), and 1.2 (0.9-1.6) in the R300, R150, and SC groups, respectively (P = NS among groups). These values increased to 7.0 (6.2-7.5), 6.9 (6.3-7.3), and 4.9 (1.9-7.3), respectively, at emergence from anaesthesia (P < 0.05 for R300 vs SC and R150 vs SC). Two minutes after administration of R300 and R150, a mean (range) gastric pH of 6.8 (5.8-7.5), and 5.6 (1.2-7.0), respectively, was reached, and remained above 2.5 for 14 hr (P = NS). Plain SC increased the gastric pH within two minutes to a mean of 6.8 (6.7-7.0), and maintained it above 2.5 for six hours (P < 0.05 for R300 vs SC at 8, 10, 12, and 14 hr after induction). We conclude that both the combination of R plus SC, and SC alone are rapidly effective in neutralizing gastric acid when administered orally after induction of anaesthesia. However, the effectiveness of plain SC is shorter-lived, and if maintenance of gastric pH above 2.5 for longer than six hours is needed, the R plus SC combination should be administered. © 1995 Canadian Anesthesiologists.