A Study on the Determination of Extracorporeal Blood Flow Rate for Extracorporeal Carbon Dioxide Removal(ECCO2R)

Lee, Kook Hyun; Kwak, Il Yong

Abstract

Extracorporeal membrane oxygenation(ECMO) is to be recommended when hypoxemia and hepercarbia are refractory to conventional treatments. Neonatal venoarterial(VA) ECMO in the USA is recognized as a therapeutic modality to neonatal respiratory failure and extracorporeal carbon dioxide removal(ECCO2R) in Europe is used for adult respiratory distress syndrome. The partial bypass using the membrane oxygenator aims at lung rest while relieving the hard ventilatory setting on the diseased lung. ECCO2R adopts low-flow venovenous(VV) bapss. VV bypass provides gas exchange without cardiac support. Venous drainage and perfusion catheters are placed in the right atrium or vena cavae via the femoral or internal jugular veins. Compared to VA bypass, the consequences of embolizations are potentially fewer and no major artery is sacrificed in ECCO2R. Highly oxygenated blood flows into pulmonary circulation which may relieve pulmonary hypertension. To evaluate the effectiveness of ECCO2R, we developed an experimental model on 7 mongrel dogs. Under general anesthesia with i. v. pentobarbital, two thin-walled polyurethane tubes in the external jugular vein and the femoral vein were connected with the extracorporeal circuit. Without ventilating the oxygenator duting VV bypass, control hemodynamic and blood gas values under conventional mechanical ventilation(CMV) were obtained. We proceeded to oxygen insufflation(OI), and extra- corporeal CO2 removal (ECCO2R) in that order. Oxygen was delivered at 300ml/min to the animal lung for OI and ECCO2R and was added at 21/min to the oxygenator only for ECCO2R. Hemodynamic parameteres did not vary among CMV, OI and ECCO2R. Arterial PH in CMV was 7.35+/-0.07 and was decreased to 7.19+/-0.05 in OI due to the increase of PaCO (70+/-3 mmHg). PaO2 was remained constant through the experiment. Mixed venous PH in CMV was 7.31+/-0.05 and was decreased to 7.15+/-0.08 in OI, Blood gas analysis values were same between CMV and ECCO2R. Carbon dioxide removal through the lung (V(L)CO2) were 47+/-3 ml/min in CMV, 9+/-3 ml/min in OI and 8+/-2 ml/min in ECCO2R. The amount of carbon dioxide removed via the oxygenator (VoCO2) was 38+/-5 ml/min in ECCO2R. The total amount of CO2 removal (VCO2) between CMV and ECCO2R was same statistically. The bypass flowrate at the lowest E(T)CO2 (end-tidal CO2) was 60+/-9 ml/min, resulting in 35+/-4% of bypass ratio. It can be concluded that ECCO2R can alleviate hypercapnea using a low flow VV bypass and may be used as an altermative of mechanical ventilator in the setting of acute respiratory failure.