in vitro evaluation of intragastric pco2 measurement by air tonometry

Objective. To assess the in vitro performance of a new device,the Tonocap®, for semi-continuous air tonometry of regionalPCO2 in the gastrointestinal tract. Methods. Thetonometer consists of an air filled balloon-tipped catheter, connected to aprototype Tonocap® system. The tonometer was placed in saline baths atsteady-state PCO2’s ranging from 0 to 105 torr, toevaluate bias, precision and reproducibility to PCO2measurements. The response time was defined as the time needed to detect 95%of an instantaneous change in bath PCO2. Results. Thebias of the PCO2 measurement (mean ± SD) was−2 ± 2% and reproducibility (coefficient ofvariation) was 2 ± 1%. The response time was 19 ± 2 min.Conclusions. Tonocap® air tonometry is simple andeliminates most sources of error associated with conventional salinetonometry. The bias, precision, reproducibility and response time invitro are consistent with a clinically reliable device.