Continuous measurement of arterial and end-tidal carbon dioxide during cardiac surgery: Pa-ETCO2 gradient

There have been reports of a negative arterial to end-tidal CO2 gradient (Pa-ETCO2) during cardiac surgery, so we used capnometry and an intravascular blood gas sensor (Paratrend 7) to continuously monitor this gradient in 20 cardiac surgical patients. We also compared the values obtained from this sensor with those obtained from a standard blood gas analyser at seven time points. We found a significant change in Pa-ETCO2 after cardiopulmonary bypass (P < 0.001) though we were unable to demonstrate a negative Pa-ETCO2 at any time (95% CI 0-14%). There was clinically acceptable agreement between laboratory and Paratrend 7 measurements during and after cardiac surgery.