Gastric tonometry in healthy volunteers: effect of ranitidine on calculated intramural pH
Department of Surgery; Department of Anesthesiology
Medical Subject Headings
*Gastric Acidity Determination; Humans; Methods; Ranitidine
OBJECTIVE: To determine if intraluminal production of CO2 leads to underestimation of gastric intramural pH (pHi) by tonometry. DESIGN: Nonrandomized controlled study.
PATIENTS: Healthy volunteers.
INTERVENTIONS: NG tonometers were placed in healthy volunteers. Some of the volunteers (n = 11) were pretreated with ranitidine to prevent secretion of protons into the gastric lumen. Others (n = 13) were untreated (i.e., gastric acid secretion was uninhibited).
MEASUREMENTS AND MAIN RESULTS: Gastric pHi was calculated from the arterial (HCO3-) and the tonometrically determined intraluminal PCO2 using the Henderson-Hasselbalch equation. Intraluminal PCO2 was significantly higher in the control group (54 +/- 14 torr [7.2 +/- 1.9 kPa]) than in the ranitidine-treated group (42 +/- 4 torr [5.6 +/- 0.4 kPa], p = .02). Mean gastric luminal pH was 1.9 +/- 0.6 in the control group as compared with 6.7 +/- 0.7 in volunteers treated with ranitidine (p less than .01). Mean calculated gastric pHi was 7.30 +/- 0.11 in the untreated group and 7.39 +/- 0.03 in the ranitidine-treated group (p less than .03).
CONCLUSIONS: These data suggest that intraluminal production of CO2 from the titration of gastric HCO3- by secreted H+ can result in the underestimation of gastric pHi by tonometry. This phenomenon can be eliminated by H2-receptor blockade.
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Citation: Crit Care Med. 1991 Feb;19(2):271-4.