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Whole blood activated clotting time in infants during extracorporeal membrane oxygenation
T P Green1, B Isham-Schopf, R H Steinhorn
1Department of Pediatrics, University of Minnesota, Minneapolis.
Insights
The activated clotting time (ACT) test monitors heparin during extracorporeal membrane oxygenation (ECMO) in infants. While ACT correlates with heparin levels, multiple tests are needed for precise anticoagulation monitoring to prevent bleeding complications.
Area of Science:
- Pediatrics
- Cardiovascular Surgery
- Hematology
Background:
- Bleeding complications are a major risk for infants on extracorporeal membrane oxygenation (ECMO).
- Heparin therapy is crucial for anticoagulation during ECMO but requires careful monitoring.
- The activated clotting time (ACT) test is the standard method for monitoring heparin during ECMO.
Purpose of the Study:
- To investigate the relationship between ACT values and blood heparin concentration in infants undergoing ECMO.
- To assess the precision and accuracy of the ACT test for heparin monitoring in this population.
- To inform strategies for optimizing anticoagulation and reducing bleeding risks during ECMO.
Main Methods:
- Studied nine infants receiving ECMO.
- Measured whole blood ACT and simultaneously determined heparin concentration.
- Analyzed the correlation between ACT and heparin, and evaluated the impact of other factors like platelet count.
- Assessed the precision of ACT measurements through duplicate determinations.
Main Results:
- A significant correlation was found between ACT and heparin concentration (r = .55 for all samples, r = .92 for mean values).
- Platelet count, fibrinogen, and fibrin degradation products did not significantly affect the ACT-heparin relationship within the studied range.
- Individual ACT results showed limited precision (mean difference of 9.2% in duplicates), with a 32% coefficient of variation for heparin estimation from a single ACT.
Conclusions:
- The ACT test is a cost-effective bedside tool for achieving target heparin concentrations in infants on ECMO.
- Satisfactory precision in heparin monitoring requires multiple ACT determinations (duplicate or serial).
- These findings support future research into optimal heparin concentrations to balance anticoagulation and bleeding risk during ECMO.
Abstract:
Bleeding complications are the principal cause of morbidity and mortality in infants treated with extracorporeal membrane oxygenation (ECMO). The whole blood activated clotting time (ACT) test is used universally to monitor heparin therapy during this procedure. To enhance our understanding of this test and improve our management of anticoagulation, we studied the relationship between the ACT and blood heparin concentration in nine infants during ECMO. The activated clotting time correlated with the simultaneously determined heparin concentration (r = .55, p less than .001 for all patients samples; r = .92, p less than .001 for mean patients values). Within the range of values found in our patients, platelet count, fibrinogen, and fibrin degradation products did not affect the ACT-heparin concentration relationship. However, the interpretation of an individual ACT result was limited by its low precision: the mean difference of duplicate determinations was 9.2%, and the estimation of heparin concentration by a single ACT had a coefficient of variation of 32%. Two commercially available techniques using different activators gave results that differed numerically but correlated well with each other. Both provided similar precision in the estimation of heparin concentration. The ACT is a low cost, bedside test whose accuracy and precision allow the achievement of target heparin concentrations required in infants during ECMO. Multiple determinations, either in duplicate or serially, are needed to achieve satisfactory precision. These data will be useful in designing future studies to determine the optimal serum heparin concentration to provide adequate anticoagulation, but avoid bleeding complications.