Atanassoff and colleagues evaluated the effects of ranitidine (R) with 0.3 molar (M) sodium citrate (SC) and plain SC on gastric pH in 25 patients who were undergoing elective surgery.

After induction of general anesthesia, gastric contents were removed using a nasogastric tube, and a pH electrode was placed in the stomach.

Eight patients were given oral ranitidine 300 mg and SC dose (Group R300), ten patients were given ranitidine 150 mg and SC dose (Group R150), and seven patients were administered 50 ml SC alone (Group SC). This was a double-blind study. Investigators measured gastric pH continuously over a 24-hr period.

• Mean (range) baseline pH value was 1.2 (0.8–1.8) in the R300 group, 1.3 (1.0–1.8) in R150 group, and 1.2 (0.9–1.6) in SC group (P = NS among groups).
• The corresponding pH values, at emergence from anesthesia, were 7.0 (6.2–7.5), 6.9 (6.3–7.3), and 4.9 (1.9–7.3), respectively (P < 0.05 for R300 vs SC and R150 vs SC).
• Two minutes after R300 and R150 administration, the mean (range) gastric pH was 6.8 (5.8–7.5), and 5.6 (1.2–7.0), respectively. It continued to be above 2.5 for 14 hr (P = NS).
• With SC alone, the gastric pH increased within two minutes to 6.8 (6.7–7.0), and remained over 2.5 for six hours (P < 0.05 for R300 vs SC at 8, 10, 12, and 14 hr after induction).

Combined use of ranitidine and SC and SC alone can both rapidly neutralize gastric acid after induction of anesthesia.

If gastric pH above 2.5 is desired to be maintained for more than six hours, ranitidine plus SC combination should be given.

Source: Atanassoff PG, Rohling R, Alon E, Brull SJ. Effects of single-dose oral ranitidine and sodium citrate on gastric pH during and after general anaesthesia. Can J Anaesth.1995;42:382.