A new simple tool for tonometric determination of the PCO2 in the gastrointestinal tract:: in vitro and in vivo validation studies

Background and objective: Following the discovery of the feasibility of assessing the adequacy of the splanchnic perfusion by means of gastrotonometry, this technique became extensively used in clinical practice and in research. At present, high-technology instruments are available for the purpose. However, there is still a need for a simple, cheap tool that is easily applicable for patients of all ages. The present article describes such a tool and presents the results of in vitro and in vivo validation measurements with it. Methods: Balloon-free tonometric probes consisting of silicone rubber tubes were developed. In vitro measurements of the uptake of CO2 inside the probes and for comparison in a conventional ballooned intestinal tonometer were made in a closed container maintained at 37 degrees C. In in vivo studies in anaesthetized dogs, the tonometric PCO2 values were determined with a tonometric probe and catheter introduced simultaneously into the ileum of the animals and the results were analysed by the Bland-Altman method. Results: The in vitro equilibration studies revealed that the filling media inside the probes equilibrated rapidly with the PCO2 content of the chamber. The data obtained from the in vivo investigations with the two different methods demonstrated a statistically significant linear association (correlation coefficient: 0.778, significance: P < 0.001). Conclusion: The new simple tonometric probe described appears to be a reliable tool with certain advantages for gastric tonometry. However, further studies are warranted before its general clinical use.