Therapy and Monitoring of Heparin-Induced Thrombocytopenia Type II in Critically Ill Patients During Continuous Venovenous Hemodiafiltration: Comparison of aPTT and Ecarin Clotting Time for Monitoring of r-Hirudin Therapy

Abstract

We conducted a survey of therapy, complications, and monitoring of heparin-induced thrombocytopenia (HIT) type II in critically ill patients during continuous venovenous hemodiafiltration (CVVHDF). We also compared activated partial thromboplastin time (aPTT) and ecarin clotting time (ECT) for monitoring recombinant (r)-hirudin therapy. Six patients with HIT type II were treated with r-hirudin and were on CVVHDF due to acute renal failure (blood flow rate 90 ml/hr, dialysate flow rate 1 L/hr, substitution 1 L/hr predilution, acrylonitrile membrane 0.9 m²). The mean duration of CVVHDF was 6.2 ± 3.6 days (range 3-17 days). Diagnosis of HIT was established 5.0 ± 1.5 days (range 3-8 days) after a decrease in the platelet count. Three of six patients had other possible reasons for thrombocytopenia apart from HIT, such as massive transfusion, sepsis, or liver cirrhosis. Three thromboembolic events occurred before the diagnosis of HIT was established, none of them during treatment of HIT with r-hirudin. In all patients the platelet count doubled or increased up to 100/nl within 2.5 ± 0.5 days. The dose-response relationship of r-hirudin and aPTT was not satisfactory ( r = 0.371). In patients receiving CVVHDF with one of two different doses of r-hirudin (1 mg/hr versus 2 mg/hr), there was no difference in aPTT ( p < 0.77) but a significant difference in ECT ( p < 0.001). The correlation between r-hirudin dose and ECT was r = 0.654 ( p < 0.0001). r-Hirudin was safe and effective in the treatment of HIT type II in critically ill patients during CVVHDF. ECT seems to be superior to aPTT for monitoring r-hirudin therapy because it correlates better with the concentrations of r-hirudin.