Continuous monitoring of gastric carbon dioxide with optical fibers: European project COMOCADOF, in vitro evaluation

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Introduction

Gastric mucosal PCO₂ is an important parameter to evaluate the splanchnic perfusion and to estimate the prognosis of critically ill patients. Saline and gas tonometry are the existing measurement methods, with air tonometry being the golden standard. The main disadvantage of this method is the relatively long equilibrium time, which only allows intermittent registrations and therefore cannot reflect rapid changes of PrCO₂.The target of the COMOCADOF project was the development of an optical fiber sensor capable of a continuous monitoring of PCO₂ inside the stomach, with high accuracy and long-term stability, able to track rapid PrCO₂ changes.

Objectives

Evaluation of the feasibility of a measurement device using an optical fiber sensor for continuous measurement of gastric PCO₂.

Methods

The COMOCADOF system consists of a fiberoptical catheter and the measurement unit. A CO₂-sensitive polymer layer is inserted into a probe head, which is fixed at the end of the optical fiber. The in vitro tests were performed in a glass test-tube containing 20 ml of sample solution, which was maintained at a temperature of 37°C. The sample solution (either physiological saline or a physiologically adjusted hydrochloric acid of pH 1.0) was flushed with 6 gas mixtures containing 0.0 to 15.0% CO₂ for defined time intervals and at a gas flow rate of 50 ml/min. The sampling rate was typically 0.8 s. The tests were performed over a period of up to 48 h. In addition, the influence of gastric juice, colored or turbid samples (such as e.g. enteral nutrition) on the stability of the optochemical sensor was tested.

Results

The table shows the original minimum requirements (target at the beginning of the project) and the achievements obtained up to now with the optical sensor for the detection of gastric carbon dioxide.

No significant influence of gastric juice, physiologically adjusted hydrochloric acid of pH 1.0, colored or turbid samples (such as e.g. enteral nutrition) was seen.

Conclusion

The COMOCADOF System allows direct continuous measurement of CO₂ in gastric juice. The main targets of the project (response time, long-term stability and accuracy) were achieved. The system seems to perform better than the existing air tonometry method. Comparative studies with an air tonometry system both in vitro and in vivo are in progress.

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