Over the last few years various studies have reported the advantage of low molecular weight heparin (LMWH) over standard unfractionated heparin (UFH). The advantages are stated to be ease of administration (once daily injection), the suggested non-requirement of monitoring for prophylaxis, fewer bleeding episodes and a greatly rôduced risk of venous thrombotic episodes when used in orthopaedic surgery. LMWH has greater bioavailability and greater duration of activity when Injected subcutaneously, with a longer biological half-life than UFH. the anti-thrombotic effects being due to the Inhibition of factor Xa. The commercial chromogenic assay tor measuring Anti-Xa activity (BERICHROM-HEPARIN) has been used as an Indicator of Fragmin activity. The method utilizes the principle that Factor Xa is inactivated by ATIII which Is catalysed by heparin. A pilot study of twenty patients undergoing either hip or knee surgery was undertaken to assess the standard dose recommended by the manufacturer (5000 IU/day lor high-risk' patients). In our study S.C. Fragmin 2500 U was given pre-operatively, with the premedication, followed by 2500 IU immediately post opetatively. The day following surgery and daily, for a total of 7 days Fragmin 50CO IU was administered at 6.00 a.m. and Anti-Xa assays collected 4 hours latee batched, and tested retrospectively. Other laboratory investigations included FBE and baseline APTT and INR. On day seven, photographs and ultrasound examination of the operated leg were undertaken. In the study 60% of patients had Anti-XA levels > 0.4 U/ml and all patients had levels > 0.2 U/mi. The mean Anti Xa level was 0.46 U/ml. These results were higher than expected. Patients with levels >0.4 U/ml being above the prophylactic range may have a higher risk of bleeding. Associated with these levels was significant blood loss. For knee surgery, the average blood loss was 1170 mis, with an average of 3.4 units transfused; for hip surgery the average toss was 1255 mis, with an average of 3.2 units transfused. In three patients unusual Wound blistering' was noted, and In 50% significant bruising was present at the operative site, with distal extension, uncharacteristic for the procedure. No clinical venous thrombosis was detected. In all patients, ultrasound was negative for thrombosis. In one patient only a DVT subsequently occurred three weeks post-operatively. In this study subjectively significant bleeding occurred with the recommended daily dose of 5000 IU SC. which may be substantiated by the higher than expected Anti-Xa levels. In order to avoid monitoring FRAGMIN for prophylaxis and m view of the above findings it is recommended that a dose réduction to 2S00 IU day be considered for knee surgery, and possibly for hip surgery. For the latter, this must be balanced against the thrombotic risks, and can only be elucidated by further studies. Over the last few years various studies have reported the advantage of low molecular weight heparin (LMWH) over standard unfractionated heparin (UFH). The advantages are stated to be ease of administration (once daily injection), the suggested non-requirement of monitoring for prophylaxis, fewer bleeding episodes and a greatly rôduced risk of venous thrombotic episodes when used in orthopaedic surgery. LMWH has greater bioavailability and greater duration of activity when Injected subcutaneously, with a longer biological half-life than UFH. the anti-thrombotic effects being due to the Inhibition of factor Xa. The commercial chromogenic assay tor measuring Anti-Xa activity (BERICHROM-HEPARIN) has been used as an Indicator of Fragmin activity. The method utilizes the principle that Factor Xa is inactivated by ATIII which Is catalysed by heparin. A pilot study of twenty patients undergoing either hip or knee surgery was undertaken to assess the standard dose recommended by the manufacturer (5000 IU/day lor high-risk' patients). In our study S.C. Fragmin 2500 U was given pre-operatively, with the premedication, followed by 2500 IU immediately post opetatively. The day following surgery and daily, for a total of 7 days Fragmin 50CO IU was administered at 6.00 a.m. and Anti-Xa assays collected 4 hours latee batched, and tested retrospectively. Other laboratory investigations included FBE and baseline APTT and INR. On day seven, photographs and ultrasound examination of the operated leg were undertaken. In the study 60% of patients had Anti-XA levels > 0.4 U/ml and all patients had levels > 0.2 U/mi. The mean Anti Xa level was 0.46 U/ml. These results were higher than expected. Patients with levels >0.4 U/ml being above the prophylactic range may have a higher risk of bleeding. Associated with these levels was significant blood loss. For knee surgery, the average blood loss was 1170 mis, with an average of 3.4 units transfused; for hip surgery the average toss was 1255 mis, with an average of 3.2 units transfused. In three patients unusual Wound blistering' was noted, and In 50% significant bruising was present at the operative site, with distal extension, uncharacteristic for the procedure. No clinical venous thrombosis was detected. In all patients, ultrasound was negative for thrombosis. In one patient only a DVT subsequently occurred three weeks post-operatively. In this study subjectively significant bleeding occurred with the recommended daily dose of 5000 IU SC. which may be substantiated by the higher than expected Anti-Xa levels. In order to avoid monitoring FRAGMIN for prophylaxis and m view of the above findings it is recommended that a dose réduction to 2S00 IU day be considered for knee surgery, and possibly for hip surgery. For the latter, this must be balanced against the thrombotic risks, and can only be elucidated by further studies.
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