Continuous Measurement of Arterial and End-Tidal Carbon Dioxide during Cardiac Surgery: P a-ET co 2 Gradient

There have been reports of a negative arterial to end-tidal CO₂ gradient (P_a-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 P_a-ETco₂ after cardopulmonary bypass (P<0.001) though we were unable to demonstrate a negative P_a-ETco₂ at any time (95% CI 0–14%). There was clinically acceptable agreement between laboratory and Paratrend 7 measurements during and after cardiac surgery.