Continuous monitoring of membrane lung carbon dioxide removal during ECMO: experimental testing of a new volumetric capnometer

Abstract

Background: Extracorporeal membrane oxygenation constitutes a complex support modality, and accurate monitoring is required. An ideal monitoring system should promptly detect ECMO malfunctions and provide real-time information to optimize the patient-machine interactions. We tested a new volumetric capnometer which enables continuous monitoring of membrane lung carbon dioxide removal (V'CO₂ML), to help in estimating the oxygenator performance, in terms of CO₂ removal and oxygenator dead space (VDsML).

Methods: This study was conducted on nine pigs undergoing veno-arterial ECMO due to cardiogenic shock after induced acute myocardial infarction. The accuracy and reliability of the prototype of the volumetric capnometer (CO₂RESET^™, by Eurosets srl, Medolla, Italy) device was evaluated for V'CO₂ML and VDsML measurements by comparing the obtained measurements from the new device to a control capnometer with the sweep gas values. Measurements were taken at five different levels of gas flow/blood flow ratio (0.5-1.5). Agreement between the corresponding measurements was taken with the two methods. We expected that 95% of differences were between d - 1.96s and d + 1.96s.

Results: In all, 120 coupled measurements from each device were obtained for the V'CO₂ML calculation and 40 for the VDsML. The new capnometer mean percentage bias (95% confidence interval limits of agreement) was 3.86% (12.07-4.35%) for V'CO₂ML and 2.62% (8.96-14.20%) for VDsML. A negative proportional bias for V'CO₂ML estimation with the new device was observed with a mean of 3.86% (12.07-4.35%). No correlations were found between differences in the coupled V'CO₂ML and VDsML measurements and the gas flow/blood flow ratio or temperature. Coupled measurements for V'CO₂ML showed strong correlation (r_s = 0.991; p = 0.0005), as did VDsML calculations (r_s = 0.973; p = 0.0005).

Conclusion: The volumetric capnometer is reliable for continuous monitoring of CO₂ removal by membrane lung and VDsML calculations. Further studies are necessary to confirm these data.

Keywords: ECLS; ECMO; V′CO2; capnometer; extracorporeal membrane oxygenation monitoring; membrane lung carbon dioxide removal; membrane lung function; oxygenator performance.