Oxygenator exhaust capnography: An in vitro evaluation

Abstract

The aim of the study was to examine whether oxygenator exhaust capnography could be used to monitor blood carbon dioxide tension in an in vitro cardiopulmonary bypass model. Carbon dioxide tension in the oxygenator s exhaust gas was measured by a capnograph and compared with that in the blood measured by blood gas analysis. Also investigated was the relationship between the capnograph's measurements and blood pH. The effects of gas and blood flow, temperature, and pH on the measurements were examined. A good correlation was found between PCO 2 measured by the capnograph and by the blood gas analyzer ( r = 0.997, P < 0.001). When the capnograph's results were corrected for 95% oxygen, the accuracy improved further. There was a significant correlation between oxygenator exhaust PCO 2 and temperature ( rs = 0.843, P < 0.05), but the difference in PCO 2 was small in the range examined. No significant correlation was found between oxygenator exhaust PCO 2 and blood or gas flow. A reasonable correlation between blood pH and oxygenator exhaust PCO 2 ( r = 0.965, P < 0.001) was found, but the metabolic component of pH could be altered without correlation with exhaust PCO 2 ( rs = 0.203). In conclusion, oxygenator exhaust capnography was used with reasonable accuracy and reliability to monitor blood PCO 2 in an in vitro cardiopulmonary bypass model.