Heparin Resistance, Antithrombin III Treatment, and Activated Clotting Time Values

To the Editor: I read with great interest the article by Despotis et al. [1]. We have observed heparin resistance before cardiopulmonary bypass (CPB) in one patient and during CPB in two patients. Although heparin was administered sequentially 400 s (445-485 s). ATIII activity was 20% 20 min and 67% 40 min after ATIII administration. In Case 3, a 58-yr-old woman was scheduled for aortic valve replacement and open mitral commissurotomy. During CPB and despite the administration of heparin (total 609 U/kg), the ACT value was <400 s. After ATIII 1000 U was given, the ACT values remained between 407 and 547 s. We postulated that the decrease in ATIII activity was the likely cause of heparin resistance in all three patients. In the second patient, the decrease in ATIII activity may have been caused by preoperative heparin treatment [3]. We observed no thrombosis of the extracorporeal circuit and no excessive postoperative bleeding, and less protamine was required to neutralize the heparin. In conclusion, we recommend that ATIII supplementation should be considered to manage heparin resistance and to increase ACT values before or during CPB in patients undergoing open heart surgery. Meral Kanbak, MD Department of Anesthesiology and Reanimation; Hacettepe University; Ankara, 06100 Turkey