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CARDIOVASCULAR ANESTHESIA

A Novel Thrombelastograph® Tissue Factor/Kaolin Assay of Activated Clotting Times for Monitoring Heparin Anticoagulation During Cardiopulmonary Bypass

Jack J. Chavez, MD^*, Donald E. Foley, MD^*, Carolyn C. Snider, MT^*, James C. Howell, CCP^*, Eli Cohen, PhD, Robert A. Muenchen, MS, and Roger C. Carroll, PhD^*

*Department of Anesthesiology, University of Tennessee Graduate School of Medicine, Knoxville, Tennessee; Haemoscope Corporation, Niles, Illinois; and the Statistical Consulting Center, University of Tennessee at Knoxville

Address correspondence to Roger C. Carroll, PhD, Department of Anesthesiology, University of Tennessee Medical Center, 1924 Alcoa Highway, Knoxville, TN 37920. Address e-mail to RCarrol1{at}utk.edu Reprints will not be available from the authors.

We used a thrombelastograph (TEG®) assay with tissue factor and kaolin (TEG® TF/K) to measure activated clotting time (ACT) in 31 patients during cardiopulmonary bypass. For comparison, ACTs were also determined by a Hemochron Jr. Signature® and a Hepcon® HMS. The TEG® TF/K correlated with both the Hepcon (r² = 0.789) and Hemochron (r² = 0.743) ACTs. The average ACT after heparin was 319 ± 119 s (mean ± SD) for the TEG® TF/K compared with 624 ± 118 s for the Hepcon instrument. To evaluate the effects of hemodilution on TEG® TF/K and Hemochron assays, ACT assays were performed on blood diluted to 50% and titrated with heparin from 0 to 6 U/mL. Both instruments showed significant (P < 0.01) changes in the ACT-versus-heparin slope, but the 0 heparin intercept for the TEG® TF/K ACTs was not significantly changed (P = 0.292), in contrast to that for the Hemochron device (P = 0.041). Both instruments also indicated the same 1.3:1 ratio of protamine to heparin for optimum heparin neutralization, with increasing ACTs at ratios >2.6:1. The TEG® TF/K ACT assay rapidly monitors heparin anticoagulation, in addition to the capabilities of this instrument to monitor platelet function, clotting factors, and fibrinolysis.

IMPLICATIONS: This study evaluates the thrombelastograph as a new assay of blood clotting times; it is activated by the addition of tissue clotting factor and kaolin and used to monitor heparin anticoagulation during cardiopulmonary bypass. The thrombelastograph assay correlates with standard assays, is faster, is less sensitive to hemodilution, and can provide more information.

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