In vitro evaluation of intragastric PCO2 measurement by air tonometry

Objective. To assess the in vitro performance of a new device, the Tonocap(R), for semi-continuous air tonometry of regional PCO2 in the gastrointestinal tract. Methods. The tonometer consists of an air filled balloon-tipped catheter, connected to a prototype Tonocap(R) system. The tonometer was placed in saline baths at steady-state PCO2's ranging from 0 to 105 torr, to evaluate bias, precision and reproducibility to PCO2 measurements. The response time was defined as the time needed to detect 95% of an instantaneous change in bath PCO2. Results. The bias of the PCO2 measurement (mean +/- SD) was -2 +/- 2% and reproducibility (coefficient of variation) was 2 +/- 1%. The response time was 19 +/- 2 min. Conclusions. Tonocap(R) air tonometry is simple and eliminates most sources of error associated with conventional saline tonometry. The bias, precision, reproductibility and response time in vitro are consistent with a clinically reliable device.