title: Gastric tonometry in healthy volunteers: effect of ranitidine on calculated intramural pH.
abstract: OBJECTIVE
  To determine if intraluminal production of CO2 leads to underestimation of gastric intramural pH (pHi) by tonometry.
  
  
  METHODS
  Nonrandomized controlled study.
  
  
  METHODS
  Healthy volunteers.
  
  
  METHODS
  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).
  
  
  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.
authors.affiliation: Department of Anesthesiology, University of Massachusetts Medical Center, North Worcester 01655.
authors.forename: S O
authors.initials: SO
authors.lastname: Heard
authors.forename: C M
authors.initials: CM
authors.lastname: Helsmoortel
authors.forename: J C
authors.initials: JC
authors.lastname: Kent
authors.forename: A
authors.initials: A
authors.lastname: Shahnarian
authors.forename: M P
authors.initials: MP
authors.lastname: Fink
mesh_terms: D005745:Gastric Acidity Determination; D006801:Humans; D008722:Methods; D011899:Ranitidine / Q000494:pharmacology*
chemical_list: D011899:Ranitidine