Trauma patients are at high risk of deep venous thromboembolism, with the majority of patients exhibiting no symptoms. Although meta-analyses report the overall incidence of deep vein thrombosis, DVT in trauma patients to be approximately 12%, the incidence of DVT in patients receiving no prophylaxis has been reported to be as high as 58%.
Although a number of factors have been purported to increase the incidence of DVT in trauma patients , including long bone fractures, pelvic fractures, and head injuries, meta-analysis suggests that only spinal fractures and spinal cord injuries independently increase the incidence of DVT in trauma patients .
Specifically, spinal cord injury has been shown to increase the risk of DVT in trauma patients threefold.
Various modalities have been used in an attempt to decrease the incidence of DVT in trauma patients and associated pulmonary embolism (PE) in trauma patients, including both low-dose unfractionated heparin and low-molecular-weight heparin (LMWH).
Unfractionated heparin acts by binding to antithrombin III, which accelerates its ability to inactivate several molecules in the coagulation cascade, including factor Xa and thrombin.
LMWH acts primarily by inhibiting factor Xa and its activity is correlated to factor Xa levels. LMWH has improved bioavailability and decreased incidence of bleeding as compared with unfractionated heparin.
Although low-dose unfractionated heparin has been shown to be very effective in reducing the incidence of DVT in trauma patients among patients undergoing elective surgery, a number of studies suggest that its effect in trauma patients is limited and that this intervention may not decrease the incidence of DVT in trauma patients .
In contrast, having originally been shown to decrease the incidence of DVT in patients undergoing orthopedic procedures, LMWH has been shown to be safe following trauma, and several reports suggest it is effective in reducing the occurrence of DVT and associated complications in the trauma population.
One landmark study demonstrated a decrease of 30% in the incidence of DVT in trauma patients and a decrease of 58% in the incidence of proximal vein thrombosis with the use of LMWH. Suggested dosage for enoxaparin is 30 mg injected subcutaneously twice a day.
It is important to note, however, that a recent review of published studies examining LMWH suggests that even this therapy may not offer significant benefit, and better quality studies are required to settle this debate.
Certain subgroups of trauma patients cannot receive either heparin or LMWH prophylaxis because of ongoing risk of hemorrhage. Generally, most clinicians avoid the use of heparin in the presence of brain and spinal cord injuries, solid organ injuries that are being managed nonoperatively, and retroperitoneal bleeding requiring transfusion.
Nevertheless, patients with these contraindications to heparin therapy can still form thrombi in the extremities and require an alternative mode of PE prevention. In these patients, inferior vena caval (IVC) filters are frequently considered an acceptable alternative. While there is convincing evidence for the use of IVC filters in patients who have known DVT in trauma patients and either cannot receive heparin or have DVTs or PE despite full anticoagulation, the timing and target population of filters inserted for prophylaxis remain debatable.
IVC filters can cause significant complications, including caval penetration, and the evidence for the use of these filters as prophylaxis in the general trauma population is equivocal.
Their use is supported in specific patterns of injury, including spinal cord injury, pelvic fracture combined with long bone fracture, severe head injury combined with long bone fracture, and complex long bone injuries.
More recently, temporary filters have been studied in the trauma population and the literature suggests they are a safe option in these patients. However, reported retrieval rates are as low as 35%, and long-term follow-up is required to assess the proportion of these devices that is ultimately retrieved.
One final note in DVT in trauma patients is that the use of enoxaparin in the setting of renal failure is problematic. The manufacturer’s package insert recommends the dose of enoxaparin to be 30 mg sq qday if the creatinine clearance is <30.
However, many experienced ICU pharmacists and clinicians recommend a dose of unfractionated heparin q8 hours for patients receiving hemodialysis or continuous venovenous hemodialysis
For further reading check
http://en.wikipedia.org/wiki/Deep_vein_thrombosis
http://www.thrombosisjournal.com/content/2/1/8