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CARDIOVASCULAR ANESTHESIA

The Detection of Changes in Heparin Activity in the Rabbit: A Comparison of Anti-Xa Activity, Thrombelastography^®, Activated Partial Thromboplastin Time, and Activated Coagulation Time

Department of Anesthesiology (Divisions of Cardiothoracic Anesthesia and Anesthesiology Research), The University of Alabama at Birmingham, Birmingham, Alabama

Address correspondence and reprint requests to Vance G. Nielsen, MD, Department of Anesthesiology, The University of Alabama at Birmingham, 619 S. 19th St., Birmingham, AL 35249-6810. Address e-mail to vance.nielsen{at}ccc.uab.edu

Thrombelastography (TEG^®) has been used to detect both exogenous and endogenous circulating heparin activity in clinical and laboratory settings. Thus, in this study I sought to compare the sensitivity of TEG^®, activated partial thromboplastin time (aPTT), and activated coagulation time (ACT) values with changes in anti-Xa activity after small-dose heparin administration in rabbits. Conscious rabbits (n = 11) had blood obtained from ear arteries for hematological analyses after the administration of 0, 10, 20, and 30 U/kg of IV heparin. Anti-Xa activities after the administration of 0, 10, 20, and 30 U/kg of heparin were, respectively, 38 ± 9 mU/mL, 74 ± 15 mU/mL, 105 ± 14 mU/mL, and 134 ± 17 mU/mL; all values were significantly different from each other. TEG^® variables (R and ) significantly (P < 0.05) changed between 0, 10, and 20 U/kg heparin doses, but a difference between 20 and 30 U/kg could not be discerned secondary to loss of a detectable clot. The aPTT was significantly (P < 0.05) different between 0, 20, and 30 U/kg doses. ACT values were significantly different between the 0 U/kg heparin dose and all other doses; however, there were no significant differences between the 10, 20, and 30 U/kg heparin doses. Changes in anti-Xa activity were significantly linearly related to R (r = 0.81, P < 0.0001), (r = -0.85, P < 0.0001), aPTT (r = 0.74, P < 0.0001), and ACT (r = 0.41, P = 0.005). In this model of small-dose heparin administration, TEG^® variables were more sensitive to changes in heparin activity than aPTT and ACT.

IMPLICATIONS: Changes in thrombelastography (TEG^®) variables more sensitively reflect changes in circulating heparin activity than activated partial thromboplastin time (aPTT) and activated coagulation time (ACT) after small-dose heparin administration in rabbits. Thus, TEG^® may be more helpful than aPTT and ACT in the detection of heparin in both laboratory and clinical settings wherein heparin may play a role in coagulopathy.

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