Journal of General Practice

End-tidal CO2 Should not be a Parameter for Ventilatory Adjustment during Low Cardiac Output States Like Off-pump Coronary Artery Bypass Grafting

Abstract

Manender Kumar Singla, Kanwalpreet Sodhi, Anupam Shrivastava, Manpreet Singh Salooja, Kishore C. Mukherjee and Sonia Saini

Background: Capnography is widely used as a non-invasive monitoring technique for intra-operative and postoperative mechanically ventilated patients. Aim: To study whether the EtCO2 values should be used to adjust mechanical ventilation during low cardiac output states such as off pump cardiac bypass surgery (OPCABG). Setting and design: Prospective study in 50 patients undergoing OPCABG. Material and Methods: The values of cardiac index (CI), EtCO2, PaCO2 and P(a-Et)CO2 gradient were compared at two time points during OPCABG: immediately before skin incision and during grafting of obtuse marginal artery, as usually OM grafting is considered to be associated with low cardiac output. Statistics: Data was analysed using student’s t-test. Results: There was a significant decrease in the value of CI from point A to point B (2.33 vs. 1.75 L/min/m2, p<0.001), significant decrease in EtCO2 from 25.28 to 21.88mmHg (p<0.001) and statistically significant increase in P(a-Et)CO2 gradient 4.39 at point A to 9.18 mmHg at point B (p<0.003). Conclusion: The decrease in EtCO2 had a positive correlation with the decrease in cardiac index. So during the low flow periods as found in OPCABG, EtCO2 cannot reliably estimate the adequacy of ventilation.