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Correlation of ACT as measured with three commercially available devices with circulating heparin level during
S D Niles1, R G Sutton, J Ploessl
1Perfusion Technology Program, University of Iowa Hospitals and Clinics, Iowa City 52242, USA.
Insights
Automated activated clotting time (ACT) devices struggle to accurately measure heparin levels during cardiopulmonary bypass (CPB). These ACT devices showed poor correlation with heparin concentrations, especially during CPB procedures.
Area of Science:
- Cardiovascular Surgery
- Hematology
- Medical Device Technology
Background:
- Activated clotting time (ACT) is crucial for monitoring anticoagulation during cardiopulmonary bypass (CPB).
- Factors like hypothermia and hemodilution can significantly impact ACT device accuracy.
- The Thrombolytic Assessment System (TAS) was suggested to be less affected by these CPB-related changes.
Purpose of the Study:
- To evaluate the correlation of the Thrombolytic Assessment System (TAS) and two other automated ACT devices (HemoTec, Hemochron) with circulating heparin levels during CPB.
- To compare the performance of these ACT devices against a reference standard for heparin quantification.
Main Methods:
- Nineteen patients undergoing moderate hypothermic CPB were studied.
- Blood samples were collected at baseline, post-heparinization, during CPB, and post-protamine.
- Circulating heparin levels were determined using an anti-factor Xa inactivation assay.
- Three automated ACT devices (TAS, HemoTec, Hemochron) were used for ACT measurements.
Main Results:
- High correlation was observed between HemoTec and Hemochron (r=0.99).
- All three ACT devices showed negative correlations with patient hematocrit during CPB (p < 0.05).
- Device correlation with the anti-Xa assay revealed significant discrepancies, particularly during CPB.
Conclusions:
- Automated ACT devices, including TAS, HemoTec, and Hemochron, exhibit an inability to accurately predict circulating heparin levels essential for CPB.
- The discrepancies in ACT device performance are amplified during CPB procedures.
- Current ACT monitoring may not provide reliable heparin assessment in CPB patients.
Abstract:
Automated activated clotting time (ACT) is utilized as the primary means of assessing anticoagulation status for cardiopulmonary bypass (CPB) procedures. Influences on the clotting cascade during CPB such as hypothermia, hemodilution, and platelet dysfunction are known to affect ACT. The recently introduced Thrombolytic Assessment System (TAS) has been reported to be less sensitive to changes in hemodilution and hypothermia during CPB than more conventional ACT devices. This study evaluated the ability of TAS, and two other commercially available automated ACT systems, the HemoTec and Hemochron, to correlate with circulating heparin levels. Reference standards for circulating heparin were determined by inactivation of factor Xa assay. Nineteen patients undergoing moderate hypothermic CPB served as subjects for this investigation. Blood samples were obtained for study at four time periods: 1) baseline (control), 2) post heparin administration (300-400 U/kg) prior to CPB, 3) during CPB, and 4) post protamine. Study results demonstrated a high correlation between the HemoTec and Hemochron (r = 0.99), increased heparin dose response on CPB compared to pre-CPB activity (p < 0.05), and a significant (p < 0.05) negative correlation between devices and patient hematocrit during CPB. Additionally, device correlation with anti-Xa assay during collection periods 2 and 3 showed negative correlations in each of the three devices evaluated. We conclude that all automated devices tested demonstrated an inability to predict circulating heparin at levels necessary for CPB, and that these discrepancies become magnified during CPB procedures.