CO2 removal for ventilatory support: a comparison of dialysis with and without carbonic anhydrase to a hollow fiber...

All CO2 in blood is in equilibrium, catalyzed by carbonic anhydrase (CA). This has prompted some investigators to consider treating ventilatory failure by using dialysis to remove HCO3-. Since there is at least 18 times more CO2 in the form of HCO3- than dissolved CO2, theoretically, lower blood flows could be used than with current extracorporeal support with artificial membrane lungs. HCO3- removal for ventilatory support has required alkalinization to compensate for the resulting acidosis and has been capable of removing 26 to 38 ml CO2/100 ml blood flow, compared to 14 ml CO2/100 ml for clinically employed silicone membrane lungs. We designed a HCO3- removal system using recirculation of dialysate through a membrane lung to remove CO2, rather than alkalinization of blood, and removed 8.8 ml CO2/100 ml. Adding CA improved this to 12.2 ml CO2/100 ml, but a conventional hollow fiber lung removed 30 ml CO2/100 ml. We conclude that the complexities of an HCO3- removal system may not be necessary with the advent of more efficient hollow fiber lungs.