Accuracy of the tonometric function of recycled gastric tonometer catheters

We investigated the accuracy of recycled gastric tonometer catheters, using a prospective laboratory model, within the Intensive Care Unit of a University teaching hospital. Ten used tonometer catheters and three new catheters were exposed to known constant PCO2 levels between 23-65 torr (3.06-8.66 kPa) in a gas mixing chamber, at a temperature of 35.5-38 degrees C and a relative humidity > 95%. The tonometer balloons were primed with normal saline, and after a 30-minute equilibration time, the saline was sampled for PCO2 measurements. Steady-state PCO2 (PCO2(SS)) and gastric mucosal pH (pHi) values were derived using a correction factor and the Henderson-Hasselbalch equation. There was no difference in the mean or distribution of PCO2(SS) values between recycled and new catheters. The PCO2(SS) values of recycled catheters were within the 95% confidence limits of those of new catheters. Individual catheter values did not differ significantly from each other (ANOVA P = 0.05). Using an arterial HCO3- value of 21 mmol/l, the calculated pHi values of used catheters varied < 1.5% of the mean pHi of new catheters. The tonometric performance of recycled gastric tonometer catheters was similar to that of new catheters when tested in vitro.