SCOTTSDALE, ARIZ. – Despite thromboprophylaxis, burn patients become hypercoagulable during recovery, putting them at increased risk of venous thromboembolism, a small, prospective study has shown.
"The hypercoagulable state is likely multifactorial, and we believe that additional prophylaxis and monitoring may be needed," Dr. Robert Van Haren said at the annual scientific assembly of the Eastern Association for the Surgery of Trauma.
Patrice Wendling/IMNG Medical Media
Dr. Robert Van Haren
Hypercoagulability has long been known to contribute to venous thromboembolism (VTE), but it’s only more recently that the increased incidence of thromboembolic complications in burn patients has been appreciated.
A study using duplex ultrasound screening reported that 23% of burn patients developed deep venous thrombosis at an average of 6.7 days after admission (J. Burn Care Rehabil. 2002;23:439-43).
More recent work reports that such in-hospital risk factors as number of operations, pneumonia, and central venous access are significantly associated with VTE after thermal injury (J. Burn Care Res. 2012;33:84-8).
Dr. Van Haren and his colleagues at the University of Miami used thromboelastography (TEG) and coagulation tests to analyze blood samples drawn from indwelling catheters upon admission and at 1 week in 24 patients. All patients were placed on unfractionated or low-molecular-weight heparin at admission.
Their median age was 49 years, 88% were male, and the median total body surface area burned was 29%. Inhalation injuries also were present in 17%.
TEG values were within normal limits at admission for clotting time (R = 11.5 minutes), initial clot formation (K = 2.8 minutes), clot kinetics (alpha angle = 54.6 degrees), and clot strength (maximum amplitude = 62.5 mm).
Repeat TEG at 1 week in 16 patients who remained hospitalized revealed significantly decreased R (8.3 minutes) and K (2.0 minutes) times, and elevated alpha angle (65.5 degrees) and maximum amplitude (73.1 mm; all statistically significant, P less than .05).
"All of these changes demonstrate that these patients became more hypercoagulable at week 1," said Dr. Van Haren, a 4th-year general surgery resident.
Coagulation tests were generally supportive of TEG findings. From admission to week 1, significant decreases were observed in median prothrombin time (17.4 seconds vs. 15.7 seconds; P = .013) and international normalized ratio (1.47 vs. 1.28; P = .013). At the same time, significant elevations occurred in protein C activity (75% vs. 93%; P = .017), protein S activity (69% vs. 76%; P = .030), antithrombin III (62% vs. 88%; P = .005), and fibrinogen (524 mg/dL vs. 676 mg/dL; P = .047).
The changes suggest a procoagulant state, and cannot be attributed to hemoconcentration, as fluid balance was more positive and hematocrit was lower on repeat samples, Dr. Van Haren reported.
The only in-hospital risk factor significant for hypercoagulability at 1 week was a pre-TEG operation, he said. Men, however, were more likely to be hypercoagulable than women.
Two patients, both male, developed a deep venous thrombosis. Contrary to previous studies, the only predictive markers of VTE were decreased partial thromboplastin time and fibrinogen and elevated prothrombin fragment 1 + 2.
During the discussion period after Dr. Van Haren’s presentation, audience members asked why hypercoagulability was evaluated at 1 week, since hypercoagulability has been shown to develop quite rapidly in trauma patients. Other questions addressed whether clinicians should use the data to increase thromboprophylaxis or begin dosing based on body mass index in burn patients.
Dr. Van Haren said the 1-week time point was somewhat arbitrary, and plans to look at earlier time periods in another cohort to determine exactly when the transition to hypercoagulability occurs. "I think the most interesting thing would be to see if you can guide your thromboprophylaxis based on TEG, and use it to titrate your dose to see if it will result in decreases in VTE rates."
The study was funded in part by grants from the Office of Naval Research and U.S. Army. Dr. Van Haren and his coauthors reported no relevant financial conflicts.