The activated clotting time in cardiac surgery: should Celite or kaolin be used?

Objectives: Both kaolin- and Celite-activated clotting times (ACT) are used to guide anticoagulation during cardiopulmonary bypass. It is unknown whether these methods lead to similar management procedures for anticoagulation in patients and are thus interchangeable in terms of bias, precision and variability.

Methods: We randomized 97 patients undergoing coronary artery bypass grafting or aortic valve replacement to either kaolin- or Celite-guided anticoagulation. The ACT was measured simultaneously with the other method. We administered 300 IU/kg heparin to obtain initial ACT values greater than 400 s and additional heparin in each group using the minimum value of duplicate measurements according to a predefined protocol. The primary end point was the total heparin dose and the number of heparin supplements.

Results: The total heparin dose per patient in the 48 Celite-guided patients was 35 271 ± 12 406 IU with 51 supplements and in the 49 kaolin-guided patients, 35 997 ± 11 540 IU ( P  = 0.77) with 56 supplements ( P  = 0.53). Postoperative thrombin generation time, fibrinolytic response time, chest tube loss and transfusion requirements were not different between the two groups. However, the methods differed in individual patients with regard to supplemental heparin ( P  = 0.002). Bias between methods at baseline was +10.3%, Celite being higher, and changed to a value of -12.9% at 2 h bypass. The coefficient of variation at baseline for individual patients was 2.6 times larger with kaolin than with Celite ( P  < 0.001). Correlation between ACT values at baseline was only 45%.

Conclusions: Kaolin- and Celite-guided management of anticoagulation is clinically not different, but the methods are not interchangeable.

Clinical registration number: www.trialregister.nl identifier 1738.