Thrombelastography Versus AntiFactor Xa Levels in the Assessment of Prophylactic-Dose Enoxaparin in Critically Ill Patients

Abstract

A standard dose of enoxaparin is frequently used for deep venous thrombosis (DVT) prophylaxis. Evidence suggests inconsistent bioavailability in intensive care unit (ICU) patients. Antifactor Xa activity (anti-Xa) has been used to monitor enoxaparin dosing but its accuracy and availability are problematic. Thrombelastography (TEG) is used to evaluate coagulation in diverse settings. The purpose of this study was to analyze whether TEG could be used to predict which enoxaparin-treated patients would develop DVT. Two hundred sixty-one simultaneous enoxaparin-active (active) and enoxaparin-neutralized (neutral) TEGs were performed in 61 surgical ICU patients over four consecutive days. Patient characteristics and anti-Xa were collected. DVT screening was per ICU protocol. Mean (+/-SEM) age was 54 (+/-2.3) years and Acute Physiology and Chronic Health Evaluation II score was 17 (+/-0.7). There were 30 trauma and 31 general surgery patients (69% men). The DVT rate was 28%. Time to clot formation (R) and percent lysis at 30 minutes were different between active versus neutralized blood (p < 0.001). R time was 1.5 minutes shorter in patients with DVT versus those without (p < 0.001) indicating hypercoagulability in DVT patients. Anti-Xa levels were similar in patients with (0.135 +/- 0.012) and without (0.135 +/- 0.007) DVT (p = 0.97). There were no differences in age, body mass index, injury severity score, Acute Physiology and Chronic Health Evaluation II score, or trauma status between DVT and non-DVT groups. TEG demonstrates differences between enoxaparin-neutralized and enoxaparin-active blood in ICU patients that may be used to guide dosing. TEG differentiates enoxaparin-treated patients who subsequently develop DVT while anti-Xa levels do not. TEG demonstrates an enoxaparin-related increase in fibrinolysis.