Feasibility of continuous CO2 removal with hydrophilic membranes at low blood flow rates

In the conventional treatment of acute respiratory distress syndrome (ARDS), high O2 concentrations and mechanical ventilation may damage the lung tissue. Extracorporeal membrane oxygenation limits damage, provides the needed O2 supply and improves survival of ARDS neonates, but not of adults. Hydrophilic membranes used in hemodialysis are more non-thrombogenic and biocompatible than those used in blood oxygenation, but their O2 transport capacity is not as high. In recent years, CO2 removal at low blood flow rates combined with apneic oxygenation and low frequency ventilation has proved promising in the treatment of ARDS. This approach makes O2 supply across ECMO membranes unnecessary; it also makes hydrophilic membranes candidates for extracorporeal CO2 removal to minimize anticoagulation and immune system activation. This paper reports on the in vitro capacity of hydrophilic polysulphone membranes to remove CO2 from carbonated pig blood into an oxygen-rich gas stream. Experiments were performed on clinical-size dialysis modules and their capacity to remove CO2 as a function of blood flow rate and membrane surface area was investigated. Membranes effectively removed CO2 , more so at increasing blood flow rates and membrane surface areas, at rates of up to 15% of the CO2 metabolic production rate. The specific CO2 removal rate was comparable to that of blood oxygenators equipped with microporous hydrophobic membranes. It is concluded that CO2 removal from slowly flowing blood with hydrophilic membranes is feasible.