Automated regional citrate anticoagulation: technological barriers and possible solutions.

Background: Large-scale adoption of regional citrate anticoagulation (RCA) is prevented by risks of the technique as practiced traditionally. Safe RCA protocols with automated delivery on customized dialysis systems are needed.

Methods: We applied kinetic analysis of solute fluxes during RCA to design a protocol for sustained low-efficiency dialysis (SLED) for critically ill patients. We used a high-flux hemodialyzer, a zero-calcium (Ca) dialysate, a dialysis machine with online clearance and access recirculation monitoring, and a separate optical hematocrit (Hct) sensor. Flow rates were Q(B) = 200 ml/min for blood; Q(D) = 400 ml/min for dialysate, with Na = 140 mmol/l and HCO(3) = 32 mmol/l; Q(citrate) = 400 ml/h of acid citrate dextrose A; ultrafiltration as indicated. The Q(Ca) was infused into the return blood line, adjusted hourly based on online Hct and a <24-hour-old albumin level.

Results: Using the SLED-RCA protocol in an anhepatic, ex vivo dialysis system, ionized Ca (iCa) was >1 mmol/l in the blood reservoir and <0.3 mmol/l in the blood circuit after citrate but before Ca infusion (Q(Ca)) with normal electrolyte composition of the blood returning to the reservoir. Clinically, SLED-RCA completely abrogated clotting, without adverse electrolyte effects. The Q(Ca) prediction algorithm maintained normal systemic iCa (0.95-1.4 mmol/l) in all patients. The high citrate extraction on the dialyzer prevented systemic citrate accumulation even in shock liver patients. Safety analysis shows that building a dialysis system for automated SLED-RCA is feasible.

Conclusion: Using predictive Q(Ca) dosing and integrating control of the infusion pumps with the dialysis machine, SLED-RCA can be near-automated today to provide a user-friendly and safe system.