Extracorporeal membrane oxygenation and V/Q ratios: an ex vivo analysis of CO2 clearance within the Maquet Quadrox-iD oxygenator

Abstract

While hypercapnia is typically well treated with modern membrane oxygenators, there are cases where respiratory acidosis persists despite maximal extracorporeal membrane oxygenation support. To better understand the physiology of gas exchange within the membrane oxygenator, CO2 clearance within an adult Maquet Quadrox-iD oxygenator was evaluated at varying blood CO2 tensions and V/Q ratios in an ex vivo extracorporeal membrane oxygenation circuit. A closed blood-primed circuit incorporating two Maquet Quadrox-iD oxygenators in series was attached to a Maquet PLS Rotaflow pump. A varying blend of CO2 and air was connected to the first oxygenator to provide different levels of pre-oxygenator blood CO2 levels (PvCO2) to the second oxygenator. Varying sweep gas flows of 100% O2 were connected to the second oxygenator to provide different V/Q ratios. Exhaust CO2 was directly measured, and then VCO2 and oxygenator dead space fraction (VD/VT) were calculated. VCO2 increased with increasing gas flow rates with plateauing at V/Q ratios greater than 4.0. Exhaust CO2 increased with PvCO2 in a linear fashion with the slope of the line decreasing at high V/Q ratios. Oxygenator dead space fraction varied with V/Q ratio—at lower ratios, dead space fraction was 0.3-0.4 and rose to 0.8-0.9 at ratios greater than 4.0. Within the Maquet Quadrox-iD oxygenator, CO2 clearance is limited at high V/Q ratios and correlated with elevated oxygenator dead space fraction. These findings have important implications for patients requiring high levels of extracorporeal membrane oxygenation support.