- Meeting abstract
- Open Access
A comparison of the response of the tonocap and saline tonometry to a change in CO2
© Current Science Ltd 1997
Published: 1 March 1997
Gastrointestinal tonometry has proven to be a useful technique to evaluate gut mucosal perfusion. The most commonly used method is saline tonometry which does not allow rapid assessment of gut luminal CO2 and is subject to sampling errors. The Tonocap (Tonometrics Division, Instrumentarium Corp, Helsinki, Finland) is a new device which can be used with the established tonometric catheters. The Tonocap fills the tonometer balloon with air rather than saline. Following an equilibration period, the gas is automatically sampled, measured with an infra-red sensor and PCO2 and calculated intramucuosal pH (pHi) are displayed. We studied the in vitro response of the Tonocap and traditional saline tonometry to a step change in PCO2.
Two TRIP sigmoid tonometers (Tonometrics Division, Instrumentation Corp, Helsinki, Finland) were placed in an air tight test chamber. In one set of experiments, the chamber was perfused with saline in a closed circuit with a roller pump and a membrane oxygenator. The oxygenator allowed for rapid change of PCO2 in the fluid. In the other set of experiments, the chamber was flushed with calibration gas. The two systems mimic the clinical situations of a fluid filled viscus or a gas filled viscus. The CO2 in the chamber could be fully changed from 0 to 5 or 10% within 60 s in the saline system, and 30 s in the gas system. One catheter was connected to the Tonocap, the other was filled with 2.5 cc saline that was analysed with an IL1610 blood gas analyser. CO2 readings were taken at different times of equilibration after a step change in CO2 from 0. Between each reading, each catheter was flushed to eliminate CO2 in the dead space. CO2 versus equilibration time was fit to an exponential function and a time constant was derived.