Preoperative prediction of postoperative deep vein thrombosis

Postoperative deep venous thrombosis in Japan. Incidence and prophylaxis

The incidence of postoperative deep venous thrombosis was investigated using the iodine-125-fibrinogen method in 256 patients undergoing major surgery. Deep venous thrombosis was found in 49 patients (15.3 percent), and nonfatal pulmonary embolism developed in one of seven patients in whom the thrombus extended to the popliteal vein. The same investigation was performed in 110 patients who wore a graduated compression stocking on one leg, with the other leg serving as a control. Deep venous thrombosis was found in 4 of 110 stockinged legs (3.6 percent) and in 16 of 110 control legs (14.5 percent). The incidence of deep venous thrombosis decreased significantly in patients who wore the stocking. An increase in femoral venous flow velocity was found in the stockinged legs by the Doppler method. The mean velocity of venous return by xenon-133 clearance was significantly greater in the stockinged legs than in the control legs. These findings were considered to support the efficacy of graduated compression stockings for the prevention of deep venous thrombosis.

Preoperative blood tests in prediction of postoperative deep vein thrombosis

Fifty six patients undergoing elective abdominal surgery were investigated preoperatively with tests of coagulation, platelet function and fibrinolysis. Ten patients developed postoperative deep vein thrombosis, detected by the labelled fibrinogen uptake test and confirmed by ascending phlebography. None of the tests showed a statistically significant difference between the group mean of patients who developed DVT and of those who did not. Potential discriminators were used to derive a prognostic index for prediction of patients who would develop postoperative DVT. An index based on two preoperative blood tests i.e. three hour fibrin digestion and APTT had a successful prediction rate of 59 percent.

Prediction and selective prophylaxis of venous thrombosis in elective gastrointestinal surgery

Clinical features were noted and routine and non-routine laboratory variables were measured before elective major gastrointestinal surgery in 63 patients aged 40 years or more. Deep-vein thrombosis (DVT), detected by routine 125I-fibrinogen leg scanning, developed in 21 patients. Five clinical variables but no laboratory variables were significantly associated with DVT: age; percent mean weight for age, sex, and height (%MW); presence of varicose veins; cigarette-smoking; and sex. The most useful discriminant index of these variables was age in years plus 1.3 x %MW. The index was validated prospectively in a further 41 patients, in 18 of whom DVT developed. The value of the index in selective prophylaxis was then assessed in a further 40 patients, of whom 24 (60%) with high-risk index received low-dose heparin (5000 units twice daily). DVT developed in 4 of the 40 patients, an incidence of 10% compared with the incidence of 37.5% (39 of 104) in the earlier studies with no prophylaxis.

Statistics in question. Assessing methods--many variables

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Venous thromboembolic disease in Klinefelter's syndrome

In a series of 412 patients with Klinefelter's syndrome observed over periods ranging from 1 to 20 years, the frequency of hypostatic ulceration, deep vein thrombosis and pulmonary embolism was found to be raised. The prevalence of past or present hypostatic ulceration was 6%, which is 20-50 times higher than in the general population. The incidence of deep vein thrombosis in subjects aged between 30 and 70 years was 22.8 cases per 10,000 patient-years at risk. In community studies the incidence of this condition is around 4 new cases per 10,000 men per year. The frequency of pulmonary embolism was 16 cases per 10,000 patient-years at risk, compared with an expected figure of 0.9 to 3 cases per 10,000 men per year.

Deep venous thrombosis after strokes in Chinese

In 35 Chinese patients suffering from strokes resulting in hemiparesis or hemiplegia, deep venous thrombosis, as detected with 125I-fibrinogen scan, occurred in the paralysed leg in five and in the normal leg in one. The total incidence of 17% was lower than that reported in the West. No clinical evidence of pulmonary embolism was seen. This report represents an objective confirmation of the low incidence of venous thrombosis in the Chinese.

Postoperative deep vein thrombosis: identifying high-risk patients

A prospective study was carried out to confirm the validity of a predictive index for patients at risk of developing deep vein thrombosis. The index, which correctly identified nine out of 10 patients and incorrectly identified seven out of 52 patients as being at risk, is based on five variable--namely, the euglobulin lysis time, serum concentration of fibrin-related antigen, age, percentage overweight for height, and presence of varicose veins. Thus a population of patients at particularly high risk of developing postoperative deep vein thrombosis may be identified preoperatively by means of this index, so that prophylaxis may be used more rationally.

Prophylaxis of postoperative deep vein thrombosis: selective use of low-dose heparin in high-risk patients

Administration of prophylactic low-dose subcutaneous heparin to prevent postoperative deep vein thrombosis is expensive, entails treating many patients unnecessarily, and causes some side effects. By using a predictive index a population of patients who are at particularly high risk of developing postoperative deep vein thrombosis may be identified preoperatively. Prophylaxis was given only to these patients, resulting in an incidence of deep vein thrombosis of 3.8% compared with 16.1% in previous studies in which no specific prophylaxis was given. By limiting prophylaxis to the group of patients identified by the predictive index as being at high risk of developing postoperative deep vein thrombosis results may be obtained that are as good as those expected from treating the whole population. Thus many patients are saved from exposure to low-dose subcutaneous heparin.

Blood rheology

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Physical conditioning augments the fibrinolytic response to venous occlusion in healthy adults

The effects of a 10-week physical-conditioning program on fibrinolytic activity at rest and after stimulation by venous occlusion were studied in 69 healthy adults 25 to 69 years old. Physical conditioning was documented by treadmill performance, and fibrinolysis was measured with a newly developed radioenzymatic assay. Whereas fibrinolysis declined at rest from 16.2 +/- 1.3 to 11.4 +/- 0.8 units (mean +/- S.E.M.) (P = 0.0017), the increment in fibrinolysis produced by venous occlusion was increased from 21.7 +/- 2.9 to 33.8 +/- 4.7 units (P = 0.0037). This augmentation was most marked in women, persons with low initial levels of stimulated fibrinolysis, and persons with low initial physical fitness. We conclude that physical conditioning can enhance the augmentation of fibrinolytic activity that occurs in response to venous occlusion. Enhanced fibrinolysis in response to thrombotic stimuli could be an important mechanism in the beneficial effect of habitual physical activity on the risk of cardiovascular disease.

Leucocyte ascorbate levels and postoperative deep venous thrombosis

Forty-four general surgical patients were included in a prospective, randomized double-blind controlled trial of ascorbic acid (500 mg b.d.) or placebo for 7 days before operation. This was to test the hypothesis that vitamin C may reduce the instance of deep venous thrombosis postoperatively. Venous blood samples were taken before entering the trial, just immediately before surgery, on the day of operation and on three further occasions at 3-day intervals postoperatively for leucocyte ascorbic acid concentration (LAC). Venous thrombosis was diagnosed using the 125I-fibrinogen test and the leg scans interpreted by Roberts' criteria. There was no significant difference in the incidence of DVT between the treatment and placebo groups. In those with DVT (n = 23) the mean LAC on the day of operation was not significantly different from that in those without DVT. However, on the sixth and ninth postoperative days LAC levels were significantly lower in the DVT group. These results suggest that the administration of ascorbic acid preoperatively does not reduce the incidence of DVT, but a striking decrease in the LAC levels in the DVT patients is in keeping with the hypothesis that the initial event in the pathogenesis of DVT is adherence of leucocytes to the venous endothelium.

The role of the fibrinolytic system in thromboembolism

The present concept of physiologic fibrinolysis was reviewed. It was concluded that the nonspecific proteolytic activity of plasmin would essentially be limited to fibrin in vivo in view of (A) the specific adsorption of activator and of plasminogen onto the fibrin surface resulting in local generation of plasmin and (B) the fact that plasmin, adsorbed to fibrin (in contrast to plasmin in the fluid phase) largely escapes from the action of antiplasmin. The hemostatic balance in the resting condition was discussed. It was concluded that under normal conditions, systemic intravascular fibrin deposition or formation must be either nonexistent or extremely limited. On the other hand, there is considerable evidence that a limited systemic fibrinogenolysis is going on in healthy individuals and that this process can be accelerated by simple physiologic procedures, such as strenuous physical exercise.

Subcutaneous ancrod in prevention of deep-vein thrombosis after operation for fractured neck of femur

In a randomised double-blind controlled trial 53 patients received 5 daily subcutaneous injections of ancrod ('Arvin') after operation for fractured neck of femur, and 52 patients received saline fractured neck of femur, and 52 patients received saline injections. Deep-vein thrombosis (D.V.T.) was detected by bilateral ascending venography or necropsy 6--16 days after surgery. The frequency of D.V.T. and bilateral D.V.T. was significantly lower in the ancrod group (P less than 0.01). The frequency of major D.V.T. (thrombi in veins proximal to the calf, or calf-vein thrombi more than 3 cm long) was also significantly lower in the ancrod group (P less than 0.001). No complications of ancrod prophylaxis occurred. Ancrod reduced plasma-fibrinogen, and hence plasma and blood viscosity, during the first week after surgery; preoperative levels of fibrinogen and viscosity were not associated with post-operative D.V.T. Subcutaneous ancrod is a simple and effective alternative to oral anticoagulants for the reduction of the frequency of D.V.T. after operation for hip fracture, and merits assessment in other high-risk groups of patients.

Surgery, venous thrombosis and anti-Xa

Deep venous thrombosis is a common and unpredictable complication of surgery. In this study it is proposed that patients who develop this complication may be predicted by a low preoperative level of a naturally occurring inhibitor of coagulation, anti-Xa. Two groups of patients were investigated. Women taking the oral contraceptive pill had lower preoperative anti-Xa levels than their non-pill controls (P less than 0.01) and in addition had a significantly higher incidence of deep venous thrombosis (DVT) following emergency surgery (P less than 0.05). In 90 patients undergoing total hip replacement, the mean preoperative anti-Xa level of those patients who developed DVT was significantly lower than those who did not (P less than 0.001). Ninety-four per cent of patients with a preoperative anti-Xa level of less than 80 per cent developed DVT. The effect of low dose heparin on anti-Xa was studied. The results suggest a mechanism for the cause of postoperative thrombosis which also permits selection of individual patients who will develop this complication.