Prediction of postoperative venous thrombosis

Evidence for the prevention of venous thromboembolism

Patients undergoing major orthopaedic surgery are at high risk of developing venous thromboembolism (VTE). VTE is preventable and venous prophylaxis consensus groups recommend that each patient is assessed for risk of VTE and then stratified into one of the three categories of risk. Rick stratification enables the choice of the most appropriate preventative interventions. This article examines a decision making framework for VTE prevention with particular focus on a validated risk assessment model (RAM) to facilitate risk stratification. The relevant literature is also scrutinised in terms of the best venous antithrombotic strategies, for patients undergoing major orthopaedic surgery, according to scientific evidence.

Pre-operative identification of patients at high risk of deep venous thrombosis after elective major abdominal surgery

Eighteen items of clinical and laboratory information were measured on the day before operation in 85 patients who underwent elective major abdominal surgery. Postoperatively, deep venous thrombosis (DVT) was detected by 125I-fibrinogen scan in 23 patients. Stepwise logistic discriminant analysis was used to identify factors which predicted DVT. Seven such factors were identified, which were then used to construct a predictive index. In descending order of predictive power, they were: age, euglobulin lysis time (ELT), previous abdominal surgery, varicose veins, antithrombin III concentration, cigarette smoking, and platelet count. Pre-operatively, the predictive index correctly identified 91% of the patients in whom DVT developed, and wrongly allocated to the high-risk group 19% of those in whom it did not. A shortened version of the predictive index based only on age and ELT (I = -11.5 + 0.133 age + 0.006 ELT) was 91% sensitive and 63% specific in the prediction of DVT. In a prospective study of 43 patients, this shortened predictive index correctly identified pre-operatively 93% of patients in whom DVT developed, and wrongly allocated to the high-risk group only 17% of those in whom it did not.

Tissue plasminogen activator concentrations in major abdominal surgery. Relationship to postoperative deep vein thrombosis

Tissue plasminogen activator (t-PA) antigen concentrations were studied in 47 patients subjected to major abdominal surgery. The 17 patients, which developed postoperative deep vein thrombosis (DVT), diagnosed with the 125I-fibrinogen uptake test, had higher levels preoperatively, and on the sixth postoperative day, when the thrombi had already formed. The reduced fibrinolytic activity in patients with a predisposition to postoperative deep vein thrombosis is thus not related to any t-PA deficiency. The postoperative fibrinolytic shutdown may however partly be due to a drop in t-PA antigen levels, at least in the patients, which developed DVT.