Dalteparin as periprocedure anticoagulation for patients on warfarin and at high risk of thrombosis.

BACKGROUND: Patients taking warfarin and at high risk for thromboembolic complications have traditionally been hospitalized for two to three days to receive standard treatment with intravenous heparin both prior to and following procedures while their international normalized ratio (INR) is subtherapeutic. OBJECTIVE: To assess the feasibility of protocol implementation for outpatient anticoagulation with low-molecular-weight heparin to eliminate or reduce the length of hospital admission needed solely for anticoagulation. METHODS: Patients included were receiving warfarin for a prosthetic heart valve, mitral valve disease with atrial fibrillation, or recent episode of venous thromboembolism. Warfarin was discontinued four days prior to the procedure. Subcutaneous dalteparin 200 units/kg was given on the two mornings prior to the procedure and restarted 12-24 hours after the procedure until the INR was in the therapeutic range. Warfarin was reinitiated on the evening of surgery. RESULTS: Twenty-four patients underwent 26 procedures. There were two minor bleeding complications, and one patient experienced a transient ischemic attack. Patients received a median of five days of dalteparin. The INR returned to the therapeutic range on the median postoperative day 4. All patients avoided two days of hospitalization prior to the procedure (i.e., no patients needed to be admitted preoperatively for anticoagulation). A median of four days would have been required for the sole purpose of postoperative anticoagulation. CONCLUSIONS: Outpatient perioperative anticoagulation with dalteparin for high-risk patients requiring long-term oral anticoagulation appears feasible and warrants further study.

Body weight does not predict for anti-Xa levels after fixed dose prophylaxis with enoxaparin after orthopedic surgery.

Enoxaparin after joint arthroplasty is effective prophylaxis against venous thromboembolism. This is usually given as a fixed dose without monitoring of anti-Xa levels. This study assesses the relationship between trough anti-Xa levels, body weight, and venous thromboembolism. Consenting patients at three institutions were treated with Enoxaparin 30 mg subcutaneously bis in die postoperatively until discharge. Chromogenic anti-Xa levels were measured on the fifth postoperative day by the method of Stachrome (Diagnostica Stago). All patients had bilateral compression doppler ultrasonography on day 10 or discharge and were followed for 12 weeks for evidence of venous thromboembolism. Eleven patients developed objectively confirmed venous thromboembolism during the study. In this study, there was poor correlation between weight and anti-Xa levels. In addition, body weight and anti-Xa levels of patients who developed venous thromboembolism were compared to those who did not and there were no significant differences between the two groups. In conclusion, this study shows that there is poor correlation of trough anti-Xa levels with body weight. Recognizing the low overall event rate this study does not support the need to monitor anti-Xa levels or adjusting the dose according to weight.

An evaluation of impedance plethysmography and 125I-fibrinogen leg scanning in patients following hip surgery.

Venous thromboembolism is a common post-operative complication in patients following hip surgery. 125I-fibrinogen leg scanning and impedance plethysmography (IPG), are often used in the detection of venous thrombi in such patients. Information on the sensitivity and specificity of these non-invasive tests for the diagnosis of venous thrombosis following hip surgery is relevant for both patient management and for choosing the appropriate outcome measure for clinical trials evaluating new prophylactic regimens. We determined the sensitivity and specificity of the IPG alone, the 125I-fibrinogen leg scan alone, as well as the combined use of the two tests from a retrospective analysis of 685 hip surgery patients who participated in clinical trials of anti-thrombotic prophylaxis. These patients were followed prospectively with non-invasive tests. Bilateral venography was attempted either when one or both screening tests became positive or on day 10-14 post-operatively if both screening tests remained negative. Adequate venography was obtained in 1,010 (73.7%) legs and thrombi were identified in 198 (19.6%) legs. The sensitivities of the IPG and leg scanning were 12.9% and 44.6% respectively; the corresponding specificities were 98.1% and 95.0%. The sensitivity of a positive result on one or both screening tests was 49.6% with a specificity of 93.9%. Therefore, leg scanning and IPG, even in combination, are not sufficiently accurate to be recommended as the only strategy for the diagnosis of venous thrombosis following hip surgery. Venography should be considered in all patients undergoing surveillance testing either when one or both of the screening tests become positive or on day 10-14 if the screening tests remain negative.