Development and validation of a technique for continuous monitoring of gastric intramucosal pH

A novel method for continuously monitoring gastric intramucosal PCO2 and pH was developed and tested. Gas was continuously circulated through a modified balloon-tipped catheter connected to an external closed system fitted with an infrared CO2 sensor to monitor PCO2. Performance of the capnometric recirculating gas tonometry (CRGT) system was tested in vitro using an equilibration chamber and in vivo in six anesthetized dogs. Serial PCO2 measurements were made using CRGT and compared with intermittent PCO2 values obtained by conventional tonometry catheters. In the animal experiments, gastric intramucosal PCO2 and pH were determined before and after inducing hypoxia by decreasing the Flo2 to 0.08. After initial placement, PCO2 determined by the CRGT reached a near plateau within 45 min, and at that time point values were comparable to those obtained by conventional intermittent tonometry. Significant increases in gastric intramucosal PCO2 were detectable by CRGT within 5 min of inducing systemic hypoxia, and there was a concomitant significant decrease in intramucosal pH. Continuous monitoring of gastric intramucosal PCO2 and pH is feasible, has potential advantages over conventional methods, and can provide significant trending information over intervals as short as 5 min.