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

Activated clotting time in inpatient diagnostic and interventional settings

Monitoring for the anticoagulant effect of unfractionated (UFH) at the point of care using activated clotting time in real time is vital where risk of thrombosis is high. Although monitoring UFH effect is a routine and important task, changing from one ACT instrument type or technology to another must be preceded by a clinical and statistical evaluation to determine the suitability and repeatability and establish normal and treatable ranges of this newer instrument. In this multi-center prospective evaluation we tested 1236 paired ACT+ samples, and 463 paired ACT-LR samples (1699 total) from enrolled study subjects. Clinical settings included CVOR cardiopulmonary bypass, at the beside in extracorporeal life support (ELS), the Cardiac Catheterization Lab (CCL) during diagnostic studies and percutaneous coronary interventions (PCI), interventional radiology procedures and EP interventions. This study found more consistent clinical performance from the GEM Hemochron 100 as compared to the current clinical model, the Hemochron Signature Elite. The bias of GEM Hemochron 100 for ACT+ and ACT-LR was greatest in the setting of the CVOR where ACT levels were high. ACT-LR measurements by the GEM Hemochron 100 were comparable to the SE when performed in settings of CCL, ECM, EP and ICU. Results obtained for both ACT-LR and ACT+ in all clinical settings in this study using the GEM Hemochron 100 are as accurate and more repeatable as those with the current clinically available Signature Elite.

Point-of-care measurement of activated clotting time for cardiac surgery as measured by the Hemochron signature elite and the Abbott i-STAT: agreement, concordance, and clinical reliability

BACKGROUND

Since inadequate heparin anticoagulation and insufficient reversal can result in complications during cardiopulmonary bypass (CPB) surgery, heparin anticoagulation monitoring by point-of-care (POC) activated clotting time (ACT) measurements is essential for CPB initiation, maintainance, and anticoagulant reversal. However, concerns exist regarding reproducibility of ACT assays and comparability of devices.

METHODS

We evaluated the agreement of ACT assays using four parallel measurements performed on two commonly used devices each (i.e., two Hemochron Signature Elite (Hemochron) and two Abbott i-STAT (i-STAT) devices, respectively). Blood samples from 30 patients undergoing cardiac surgery on CPB were assayed at specified steps (baseline, after heparin administration, after protamine administration) with four parallel measurements (two of each device type) using commercial Kaolin activated assays provided by the respective manufactures. Measurements were compared between identical and different device types using linear regression, Bland-Altman analyses, and calculation of Cohen's kappa coefficient.

RESULTS

Parallel i-STAT ACTs demonstrated a good linear correlation (r = 0.985). Bias, as determined by Bland-Altman analysis, was low (- 3.8 s; 95% limits of agreement (LOA): - 77.8 -70.2 s), and Cohen's Kappa demonstrated good agreement (kappa = 0.809). Hemochron derived ACTs demonstrated worse linear correlation (r = 0.782), larger bias with considerably broader LOA (- 13.14 s; 95%LOA:-316.3-290 s), and lesser concordance between parallel assays (kappa = 0.554). Although demonstrating a fair linear correlation (r = 0.815), parallel measurements on different ACT-devices showed large bias (-20s; 95% LOA: - 290-250 s) and little concordance (kappa = 0.368). Overall, disconcordant results according to clinically predefined target values were more frequent with the Hemochron than i-STAT. Furthermore, while discrepancies in ACT between two parallel iSTAT assays showed little or no clinical relevance, deviations from parallel Hemochron assays and iSTAT versus Hemochron measurements revealed marked and sometimes clinically critical deviations.

CONCLUSION

Currently used ACT point-of-care devices cannot be used interchangeably. Furthermore, our data question the reliability of the Hemochron in assessing adequacy of heparin anticoagulation monitoring for CPB.