Small bowel tonometry is more accurate than gastric tonometry in detecting gut ischemia

Gastric tonometerPCO₂ measurement may help identifygut ischemia in critically ill patients but is frequentlyassociated with large measurement errors. We tested the hypothesis thatsmall bowel tonometer PCO₂measurement yields more accurate information. In 10 anesthetized,mechanically ventilated pigs subject to progressive hemorrhage, wemeasured gut oxygen delivery and consumption. We also measuredtonometer PCO₂ minus arterialPCO₂(PCO₂) and calculated the corresponding intracellular pH from tonometers placed in the stomach and jejunum. We found that the correlation coefficient(r²) forbiphasic gut oxygen delivery-PCO₂relationships was 0.29 ± 0.52 for the gastric tonometer vs. 0.76 ± 0.25 for the small bowel tonometer(P < 0.05). In addition, thecritical gastric tonometer PCO₂was excessively high and variable (62.9 ± 39.6) compared with thecritical small bowel tonometerPCO₂ (17.0 ± 15.0, P < 0.01). Small bowel tonometerPCO₂ was closely correlated withsuperior mesenteric vein PCO₂(r² = 0.81, P < 0.001), whereas gastrictonometer PCO₂ was not(r² = 0.13, P = not significant). Weconclude that measurement of gastric tonometerPCO₂ yields excessively noisy andinaccurate data on the onset of gut anaerobic metabolism in hemorrhagicshock. Small bowel tonometer PCO₂ isless noisy and, as a result, is superior in detecting gut hypoperfusionand the onset of anaerobic metabolism.