[Contact phase activation can occur with certain types of activated carbon]

HFR is an integrated hemodiafiltration system that utilizes a double chamber filter to separate convection from diffusion. The ultrafiltrate is regenerated by passage through a sorbent cartridge made up of resin and activated carbon. A small percentage of patients using this technique had gastrointestinal symptoms that included nausea/vomiting, diarrhea and/or stomach cramps approximately 1-2 hours after the start of HFR. We undertook a series of investigations to try and elucidate the cause of these reactions. Since the majority of the patients were taking ACE inhibitors, attention was focused on contact phase activation. Healthy and uremic plasma were incubated with different components of the HFR circuit. The activated carbon caused a moderate activation of factor XII and production of kallikrein, while there was no activation for the lines, double filter or resin. Patients taking ACE inhibitors may be at risk for treatments involved with contact phase activation as ACE inhibitors also block the degradation of bradykinin. A new sorbent cartridge has now been developed that contains only resin.