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

Manender Kumar Singla

doi:10.4172/2329-9126.1000159

Abstract

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.

Highlights

Capnography is routinely used in monitoring of intra-operative and postoperative mechanically ventilated patients [1]
There was a significant decrease in the value of cardiac index (CI) from point A to point B (2.33 vs. 1.75 L/min/m2, p
The decrease in EtCO2 had a positive correlation with the decrease in cardiac index

Summary

Introduction

Capnography is routinely used in monitoring of intra-operative and postoperative mechanically ventilated patients [1]. It is a non-invasive technique used for continuous measurement of exhaled carbon dioxide (CO2) throughout the respiratory cycle, commonly referred to as end-tidal CO2 (PEtCO2 or EtCO2) [2]. As PEtCO2 is governed by pulmonary blood flow, it may not be true in conditions with acutely low CO [1,8] In these situations, there is an increase ventilation-perfusion ratio (V/Q), which decreases PEtCO2 and increases P(a-Et)CO2 [1]. Capnography is widely used as a non-invasive monitoring technique for intra-operative and postoperative mechanically ventilated patients

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Conclusion