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

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.