Correspondence

Prophylaxis against Venous Thromboembolism after Major Trauma

N Engl J Med 1997; 336:586-587February 20, 1997

Article

To the Editor:

We view with concern the claim of Geerts et al. (Sept. 5 issue)1 that the potent anticoagulant low-molecular-weight heparin can safely be used as routine prophylaxis against deep venous thrombosis in trauma victims. The study compared low-dose heparin with low-molecular-weight heparin in a cohort of 265 patients. The authors found that deep venous thrombosis occurred at a higher rate in the low-dose–heparin group (60 of 136 patients, or 44 percent) than in the low-molecular-weight–heparin group (40 of 129, or 31 percent; P = 0.014). Thus, 18 (60 minus 31 percent of 136) cases of deep venous thrombosis may have been prevented in the group that received low-molecular-weight heparin. This reduction in the rate of deep venous thrombosis was purchased, however, at the price of five episodes of severe hemorrhage in the low-molecular-weight–heparin group, including one subdural hematoma requiring operative drainage. Geerts et al. note that only one episode of bleeding (a nosebleed) occurred in the low-dose–heparin “control” group but claim that there was no difference between the two groups on the basis of a Fisher's exact test P value of 0.12.

The real concern in patient care is not deep venous thrombosis but pulmonary embolism. Ironically, the single pulmonary embolism that occurred in this study was in a member of the low-molecular-weight–heparin group. Other therapies have been proposed to deal with potential pulmonary embolism that do not pose the risk of anticoagulation. The Greenfield vena caval filter has been successfully employed in several prospective studies with minimal morbidity and a significant reduction in the incidence of pulmonary embolism.2,3

Thus, the authors have misunderstood the risks that trauma patients face. Deep venous thrombosis is usually asymptomatic and rarely fatal. Hemorrhage is the constant and paramount risk. Anticoagulation therapy for such patients has led to complications in these authors' hands. Overall, 18 probably asymptomatic deep venous thromboses were prevented by a therapy that caused five clinically relevant episodes of hemorrhage.

Turner Osler, M.D.
Frederick Rogers, M.D.
University of Vermont, Burlington, VT 05405-0068

3 References

1. 1

   Geerts WH, Jay RM, Code KI, et al. A comparison of low-dose heparin with low-molecular-weight heparin as prophylaxis against venous thromboembolism after major trauma. N Engl J Med 1996;335:701-707
   Full Text | Web of Science | Medline

2. 2

   Rogers FB, Shackford SR, Ricci MA, Wilson JT, Parsons S. Routine prophylactic vena cava filter insertion in severely injured trauma patients decreases the incidence of pulmonary embolism. J Am Coll Surg 1995;180:641-647
   Web of Science | Medline

3. 3

   Rodriquez JL, Lopez JM, Proctor MC, et al. Early placement of prophylactic vena cava filters in injured patients at high risk for pulmonary embolism. J Trauma 1996;40:797-797
   CrossRef | Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: Unfortunately, Osler and Rogers misconstrue both the objectives of our study and its results. We designed an efficacy trial using total deep-vein thrombosis, detected by contrast venography, as the primary outcome. While we clearly demonstrated the superior efficacy of the low-molecular-weight heparin enoxaparin over low-dose heparin in reducing the total rate of deep-vein thrombosis, we also emphasized enoxaparin's 58 percent reduction in the risk of proximal deep-vein thrombosis — an outcome of greater clinical importance. Eventually, we hope that investigators will demonstrate in effectiveness studies that thromboprophylaxis decreases the rate of clinically important thromboembolic events. However, our important first step involved performing a double-blind, randomized trial with a sensitive and objective measure of outcome.

Despite the early use of anticoagulant prophylaxis, bleeding was uncommon (occurring in less than 2 percent of patients). We described the six bleeding episodes so that readers could make their own decision about which were clinically relevant. “Severe hemorrhage” occurred in only one patient, and there were no significant differences between the bleeding studies in the two groups. The observed bleeding rate, according to the same definition, was also equivalent to that in studies of elective arthroplasty. This low risk of clinically significant bleeding is important, since it provides strong reassurance that anticoagulant prophylaxis can be safely used in patients with major trauma.

We do not misunderstand the risks that trauma patients face. On the contrary, the two primary authors have personally seen and followed until discharge every trauma patient at our center for more than five years. Although we and our surgical colleagues share the concern about the potential for bleeding in these patients, we have been impressed with the absence of clinical bleeding associated with an aggressive prophylaxis regimen based primarily on the use of enoxaparin. To date, we have not encountered serious bleeding complications in these patients that could be attributed to the prophylaxis.

Finally, there is not a single published trial in which trauma patients were randomized to the use of a vena caval filter. We agree that the use of filters may well be associated with fewer pulmonary emboli as compared with no prophylaxis or ineffective prophylaxis. The important as yet unresolved issue, however, is the benefit and cost effectiveness of filters when added to a prophylaxis regimen proved to be efficacious. In the meantime, it is imprudent to recommend the use of an invasive, permanent, and very costly device that is associated with both short-term and long-term complications and that increases the incidence of deep-vein thrombosis until evidence from at least one methodologically sound trial demonstrates that the use of filters is necessary or cost effective.

Our data provide strong evidence that low-molecular-weight heparin is an effective, safe method of prophylaxis in this extremely high risk group of patients. We encourage physicians interested in the care of trauma patients to advocate evidence-based thromboprophylaxis strongly and to contribute to well-designed trials in this area.

William H. Geerts, M.D.
Richard M. Jay, M.D.
University of Toronto, Toronto, ON M4N 3M5, Canada

Citing Articles (2)

Citing Articles

1. 1

   Frederick B. Rogers, Mark D. Cipolle, George Velmahos, Grace Rozycki, Fred A. Luchette. (2002) Practice Management Guidelines for the Prevention of Venous Thromboembolism in Trauma Patients: The EAST Practice Management Guidelines Work Group. The Journal of Trauma: Injury, Infection, and Critical Care 53:1, 142-164
   CrossRef

2. 2

   George C Velmahos, John Nigro, Raymond Tatevossian, James A Murray, Edward E Cornwell, Howard Belzberg, Juan A Asensio, Thomas V Berne, Demetrios Demetriades. (1998) Inability of an aggressive policy of thromboprophylaxis to prevent deep venous thrombosis (dvt) in critically injured patients: are current methods of dvt prophylaxis insufficient?. Journal of the American College of Surgeons 187:5, 529-533
   CrossRef