Intra-operative antithrombotic therapy with low molecular weight heparin in aortic surgery. How should heparin be...

This prospective study evaluates, for the first time, the efficacy of heparinisation with low molecular weight heparin (LMWH) in aortic surgery and identifies the most effective route of administration for heparin. Sixteen patients undergoing abdominal aortic grafting for aneurysmal and occlusive disease were studied. They were randomised to receive 10,000 anti Xa units of LMWH either intravenously or directly into the aorta before or after aortic cross-clamping. Serial venous blood samples and a paired arterial sample from the superficial femoral artery were taken for the estimation of systemic and lower limb heparin activity. All three methods of administration gave therapeutic levels of heparin in the systemic and lower limb circulation. Intravenous and aortic administration before clamping resulted in significantly higher systemic levels when compared with aortic injection after clamping (p less than 0.05 Mann-Whitney U test). Intra-aortic administration resulted in a significantly higher heparin activity in the lower limb when compared with the intravenous route (p less than 0.05). No patient developed distal thrombosis. This study demonstrates that the most effective way of giving heparin in aortic surgery is by direct injection into the aorta. Administration of LMWH after cross-clamping results in less systemic activity which may help to reduce any haemorrhagic side effects.