Intravascular carbon dioxide monitoring using micro-flow colorimetry.

An intravascular carbon dioxide sensor is investigated which employs continuous perfusion of micro-quantities of reagent through silicone membrane tubing in contact with blood. Blood is sampled from a vessel by periodic withdrawal-reinfusion through a catheter and passes by the sensor membrane tubing integrated into the catheter system. Blood CO2 equilibrates across the silicone membrane causing a color change in the reagent micro-flow stream that is detected by an optical cell external to the vessel. In vivo trials on pigs demonstrate a stable sensor response, a fast response time, and high signal-to-noise ratios. The sensor also exhibits an immunity to temperature changes, reduced intravascular blood flow, photobleaching, and leaching. It has a 2 min response time, a +/-2 mmHg resolution, and minimal drift over a 12 h duration. Using a pig model, measured values compared with true values indicate a 0.998 correlation coefficient, a 1.3 mmHg precision, and a 1.7 mmHg bias.