Saturday, September 27, 2003

DVT and the complications thereof are in the media a lot lately. Aventis has their "killer legs" advertising campaign out in an effort to sell some Lovenox. The New England Journal of Medicine has papers about a randomized trial of d-dimer in the diagnosis of DVT, as well as a review of the evaluation of pulmonary embolus. (Sorry, full text requires subscription)
The d-dimer paper describes a trial comparing d-dimer to ultrasound in the diagnosis of DVT in outpatients. The authors report that a negative d-dimer effectively rules out DVT in outpatients. At my institution we have used the d-dimer as a method to determine the need to call out a tech to do a duplex exam. If the d-dimer was negative, the ultrasound would be done the next day. This has probably kept several good techs from leaving, as they were being called in to duplex every swollen leg. The problem is that a positive d-dimer doesn't rule in a DVT, since many other conditions can cause an elevated d-dimer (surgery, pregnancy, ect..).
The clinical practice paper is a good overview of the clinical, laboratory, and imaging studies used to evaluate a patient for pulmonary embolus. Conventional pulmonary angiography is heavily emphasized as a diagnostic test. The last pulmonary angiogram I saw was in medical school. It would be difficult to persuade a radiologist to do one today. Fortunately I have the advantage of a 16 slice helical scanner at my institution, which is very accurate in ruling a PE in or out.
Something we have started to use at my institution is a retrievable caval filter. This is attractive for use in the trauma patient. Trauma patients are at a high risk for DVT/PE both from the hypercoagulability associated with their injury, as well as prolonged immobility. While compression devices and SQ heparin can help prevent DVT, they are not perfect, and some patients (solid organ injury, early spinal injury and cerebral hemorrhage) cannot be placed on heparin. Filters have been proven to prevent pulmonary emboli in trauma patients. Because the risk of thromboembolism in trauma patients is only short-trerm, and occurs (for the most part) in young patients, permanent filters are not all that attractive. There is also the rarity of thromboembolism, as a study revealed that about 60-70 filters would have to be placed to save one life. However, while rare, a PE can be devastating. This system is deployed through a 6 french sheath, and may be removed (and replaced if neccesary) within 4-6 weeks via a percutaneous technique. This filter can be used in larger vessels (30mm) than the conventional "Greenfield" filter. This is still an off-label use. Thre are other reusable filters this is the only one that can be retrieved via a femoral approach, eliminating the risk of pneumothroax. The indications for the use of this filter may expand to make this a viable treatment alternative for the non-trauma patient.
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