Assessment of a new prototype hydrogel CO₂ sensor; comparison with air tonometry

a>Abstract a>Objective Gastrointestinal ischemia is always accompanied by an increased luminal CO2. Currently, air tonometry is used to measure luminal CO2. To improve the response time a new sensor was developed, enabling continuous CO2 measurement. It consists of a pH-sensitive hydrogel which swells and shrinks in response to luminal CO2, which is measured by the pressure sensor. We evaluated the potential clinical value of the sensor during an in vitro and in vivo study. a>Methods The response time to immediate, and stepwise change in pCO2 was determined between 5 and 15 kPa, as well as temperature sensitivity between 25 and 40 °C at two pCO2 levels. Three sensors were compared to air tonometry (Tonocap®) in healthy volunteers using a stepwise incremental exercise test, followed by a period of hyperventilation and an artificial CO2-peak. a>Results The in vitro response time to CO2 increase and decrease was mean 5.9 and 6.6 min. The bias, precision and reproducibility were +5%, 3% and 2%, resp. Increase of 1 °C at constant pCO2 decreased sensor signal by 8%. In vivo tests: The relation with the Tonocap was poor during the exercise test. The response time of the sensor was 3 min during hyperventilation and the CO2 peak. a>Conclusion The hydrogel carbon dioxide sensor enabled fast and accurate pCO2 measurement in a controlled environment but is very temperature dependent. The current prototype hydrogel sensor is still too unstable for clinical use, and should therefore be improved.