Membrane materials for blood purification in critical care

Since therapeutic conditions, especially the amount of dialysate, are usually limited in continuous renal replacement therapy (CRRT), selecting an appropriate membrane is more crucial than that in chronic hemodialysis. Under such circumstances, the use of a membrane with adsorption is expected to remove a larger amount of target substances in CRRT. Five commercial dialyzers were investigated to demonstrate the importance of membrane characteristics. The adsorptive characteristics of polymethylmethacrylate (PMMA) membrane were relatively low for cytochrome c (MW 12,400), very strong for alpha-chymotrypsinogen A (MW 25,000) and relatively strong for albumin (MW 66,000), which may be understood that the adsorption in PMMA has the optimal molecular size. On the other hand, polyacrylonitrile showed relatively low affinity and polysulfone showed essentially no affinity to these protein molecules. Time- and concentration-dependent characteristics of clearance for these proteins were also demonstrated in PMMA. Then we concluded that adsorption found in PMMA may be due to the occlusion of protein molecules into pores of entirely dense membrane. Selecting membrane materials is, therefore, important not only in removing inflammatory cytokines but also in considering the loss of albumin in clinical treatments because even albumin can be adsorbed by the membrane used in blood purification therapies.