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High dose thrombin time versus the activated clotting time during cardiopulmonary bypass
1University Hospital Rotterdam, Department of Extracorporeal Circulation, The Netherlands.
Insights
The High Dose Thrombin Time (HiTT) may not reliably predict adequate Activated Clotting Time (ACT) levels during cardiopulmonary bypass. Individual patient testing is recommended to establish safe HiTT targets for heparin monitoring.
Area of Science:
- Cardiovascular Science
- Hematology
- Medical Device Technology
Background:
- Activated Clotting Time (ACT) and High Dose Thrombin Time (HiTT) are used to monitor anticoagulation during cardiopulmonary bypass (CPB).
- Manufacturer recommendations suggest comparative ACT/HiTT assays in cardiac surgery patients.
Purpose of the Study:
- To compare the High Dose Thrombin Time (HiTT) with the Activated Clotting Time (ACT) during cardiopulmonary bypass (CPB).
- To evaluate the reliability of a standardized HiTT target for achieving adequate ACT levels in non-aprotinin treated patients.
Main Methods:
- Comparison of HiTT and ACT values in 20 non-aprotinin treated patients undergoing CPB.
- Heparinization administered at 300-400 IU/kg body weight.
- Analysis of correlation between HiTT and ACT before and during CPB.
Main Results:
- 8 out of 20 patients failed to reach the target ACT of 480 seconds despite HiTT values exceeding the target of 190 seconds.
- A poor correlation (r = 0.38) was observed between HiTT and ACT.
- Patients receiving 400 IU/kg heparin showed low ACT and high HiTT values.
Conclusions:
- A standardized HiTT target of 190 seconds does not guarantee an adequate ACT of 480 seconds for individual patients.
- The determination of target HiTT values requires careful consideration.
- Individualized comparative ACT/HiTT assays are suggested to establish safe target times for heparin monitoring during CPB.
Abstract:
In this study we compared the High Dose Thrombin Time (HiTT) with the Activated Clotting Time (ACT) during cardiopulmonary bypass (CPB) in non-aprotinin treated patients. On the advice of the HiTT test manufacturer each institution should perform comparative ACT/HiTT assays in the cardiac surgery population. In previous tests our target ACT value of 480 seconds corresponds with a mean HiTT value of 190 seconds. Our results showed that after heparinization (300-400 IU/kg body weight) 8 out of 20 patients did not reach the target ACT of 480 seconds, while the HiTT results in those 8 patients were higher than our target time of 190 seconds. Four heparin pretreated patients who received 400 IU/kg heparin, had relatively low ACT values (467 +/- 14 sec.) and high HiTT values (324 +/- 47 sec.). Before and during CPB there was a poor correlation between the HiTT and ACT (r = 0.38). The results of this study show that for the individual patient the target HiTT of 190 seconds is no guarantee for reaching an adequate ACT of 480 seconds. Although the HiTT may be a very useful assay for monitoring heparin effects during CPB, the determination of the target time can be a point of discussion. In contrast of the advice of the manufacturer we therefore suggest that comparative ACT/HiTT assay should be done in every individual patient to determine a safe target HiTT time, instead of the whole group of patients.