Measurement of the activated clotting time during cardiopulmonary bypass: differences between Hemotec® ACT and Hemochron® Jr apparatus

Abstract

Background: Measurement of the activated clotting time (ACT) represents a standard method for coagulatory assessments. The test employs specific agents to trigger the coagulation process. The present study aimed to compare kaolin (Hemotec®) versus a combination of silica, kaolin and phospholipid (Hemochron® Jr) ACTs. Methods: Hemotec® and Hemochron® Jr ACT monitors were compared by simultaneous measurement of paired arterial blood samples ( n-114) with respect to precision and bias during clinical conditions of cardio-pulmonary bypass (CPB). The influence of haemodilution on the ACT was tested in an ex-vivo model. Results: The precision of Hemotec® and Hemochron®Jr ACT measurements attained 21±2.6 s versus 27.0±2.6 s( p= 0.126) during CPB and 2.5±2.2 s versus 9.4±6.9 s ( p= 0.000) after protamine administration, respectively. The Hemochron® Jr monitor was associated with a bias of −102±13.7 s compared to the Hemotec® ACT monitor ( p= 0.000) during CPB and −6.9±2.9 s after protamine ( p= 0.025). Linear regression analysis of ACT readings between monitors reached r- 0.526 ( p= 0.000). Hemochron® Jr ACT values correlated with the erythrocyte volume fraction r- 0.379 ( p= 0.000). Ex-vivo data indicated that the Hemotec® ACT monitor was associated with relatively higher ACT readings after haemodilution. Conclusion: The ACT is not a standardized measure. Test results are strongly associated with the specific compounds used to initiate the coagulation process.