Purpose: This study compares the balloon air tonometry method of measuring gastric mucosal CO2 to standard saline tonometry. Also, this study investigates the effect of histamine-2 receptor blockade on the precision of tonometric measures of gastric mucosal PCO2 (PtCO2).
Materials and methods: We obtained hourly measurements of PtCO2 from two gastric tonometers inserted orally in 19 healthy volunteers. One tonometer measured PtCO2 by the intermittent saline method, whereas the other measured PtCO2 using a newer continuous air method. Subjects received intravenous 5% dextrose during the first 6 hours of the experiment followed by a continuous infusion of a solution of ranitidine in 5% dextrose for another 6 hours. The ranitidine infusion was titrated to maintain gastric fluid pH > or = 4.
Results: Comparison of air to saline tonometry yielded a bias of -1.3 mm Hg with a limit of agreement of 6.6 mm Hg under optimal conditions of optimal gastric fluid pH (gastric fluid pH > or = 5.0). Measures of PtCO2 were lower with ranitidine for either group, 45.3 +/- 1.3 mm Hg versus 39.7 +/- 0.5 mm Hg for saline (P < .01) and 45.9 +/- 1.0 versus 41.3 +/- 0.5 for air (P < .01). The mean PCO2 gap (PtCO2-P(arterial)CO2) at gastric fluid pH > or = 5.0 was 1.4 mm Hg, with a standard deviation of 2.7 mm Hg. A span of three standard deviations yields a normal limit for PCO2 gap of 9.5 mm Hg.
Conclusion: Measures of PtCO2 with the air tonometer method are similar to those obtained with saline tonometry. The reliability of PtCO2 measurements with either method improved with the use of ranitidine to maintain gastric fluid pH > or = 5.