Thromboprophylaxis in non-surgical patients: who, when and how?

Because of the serious lack of useable, relevant information, most recommendations for prevention of thrombosis in non-surgical patients are extrapolations from much larger clinical trials experienced in surgery. Directly relevant evidence comes predominantly from very small randomized trials, many of them open label and carried out more than 20 years before the introduction of more recent and important changes in clinical care that may have substantially reduced the baseline thrombosis risk. In these early studies, low-dose heparin and low-molecular-weight heparins prevented subclinical deep vein thrombosis in ischaemic stroke, myocardial infarction and among elderly medical inpatients. Although it is likely that these drugs also prevent subclinical deep vein thrombosis after spinal cord injury or other major trauma, and when patients require intensive medical care, the supporting evidence in these circumstances comes mainly from cohort studies and poorly controlled comparisons. In contrast, the heparins have not reduced mortality or demonstrably prevented pulmonary embolism after ischaemic stroke or among elderly medical inpatients in large and well-conducted clinical endpoint trials, from which no clinically important benefit could be demonstrated. From analyses it is suggested that such benefit is probably more difficult to demonstrate for medical than for surgical patients. In the absence of sufficient information that is specific to medical patients, various forms of prophylaxis known to be effective in surgery will continue to be applied in high-risk individuals. After venous thromboembolism, it now appears that the best duration of oral anticoagulant therapy to prevent a recurrence is determined to a greater extent by whether the thrombotic episode was idiopathic or triggered by a clinically recognizable cause, whether it was transient or continuing, and whether the deep vein thrombosis was extensive, limited to the calf veins or was a first or recurrent event.