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Health Informatics Unit
The University of Adelaide
SA 5005 Australia
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Post-operative Deep Vein Thrombosis (DVT)

Michael Edmonds

The risk of post-operative DVT is substantial, with at least a quarter of general surgery patients, and up to a half of orthopaedic surgery patients developing it in the absence of prophylaxis. This has a subsequent pulmonary embolism (PE) rate in the surgical population of 1.6%, and the mortality rate from this alone is as high as 0.3% percent of all patients undergoing surgery.

There is an enormous amount of information in the area of DVT. We chose over 200 articles to review for this study. The information comes from a wide range of trials and reviews in a variety of populations. One of the main divisions is between medical and surgical studies. Since we are considering post-operative DVT, we obtained most of our information from surgical studies. Many studies use an orthopaedic sample because a higher incidence rate allows a smaller sample size to be used. Trial design needs to be considered, together with methods used such as diagnostic technique. Clinical diagnosis of DVT or PE from signs and symptoms is notoriously unreliable, and routine objective testing must be used for valid results. Each technique has its advantages and disadvantages, but the "gold standards" for diagnosis are bilateral ascending venography for DVT, and pulmonary angiography for PE. Both of these procedures are highly invasive, and their use in trials has been limited.

Our final decision model is shown below. This shows, on the left, the risk factors of age, obesity, varicose veins, past history of thromboembolism, oral contraceptive pill (OCP), Factor V Leiden mutation, malignancy, anaesthetic type, and operation type. The occurrence of DVT is also influenced by the decision to give prophylaxis. The potential post-operative pathways for DVT are also shown on the right, incorporating development, investigation and management of clinical DVT, the possible progression onto a pulmonary embolism (PE) and the possible consequences. The measure of utility for this model is cost, which is derived from the cost of prophylaxis itself and the cost of extended hospital stay if complications arise.

Decision Model for Post-operative DVT