Deep vein thrombosis: effect of graduated compression stockings on distension of the deep veins of the calf.

The mechanisms by which graduated compression stockings prevent deep vein thrombosis are not completely understood. Recent work has suggested that venous distension plays a role in initiating the process. Our previous work has shown that the deep veins of the lower limb distend in patients undergoing surgical procedures. We have investigated 40 patients receiving surgical treatment on the abdomen or neck. A medial gastrocnemius vein was studied using ultrasound imaging during the operations. In half the patients a graduated compression anti-embolism stocking was applied to the limb under study at the start of the operation, immediately after initial measurements of vein diameter. The median vein diameter in both groups was the same at the start of the operative procedures (control, 2.6 mm, interquartile range 2.1-3.3 mm; stocking, 2.6 mm, interquartile range 2.1-3.7 mm). After application of a stocking the median diameter in this group fell to 1.6 mm (interquartile range 1.3-2.8 mm) and then decreased slightly at the end of the operation. In the control group the vein diameter increased to 2.9 mm (interquartile range 2.3-4.0 mm) during the operative procedure.

Clinical assessment of venous thromboembolic risk in surgical patients.

Prophylaxis against postoperative venous thromboembolism should be tailored according to the patient's level of risk. However, risk assessment is not yet in widespread use in surgical practice. In this study, 538 general surgical patients were prospectively assessed based on a scoring system containing 20 risk factors. Depending on the total risk factor score, the patients were grouped into low (0 to 1, 34.5%), moderate (2 to 4, 48.5%), or high risk (more than 4, 17.2%) categories. Statistically significant (p less than 0.0001) correlation was found between our results and those of three existing risk assessment systems. Overall, of the 538 patients, 37.2% received prophylaxis; 10%, 42.1%, and 76% received prophylaxis in the low-, moderate-, and high-risk categories, respectively. Mechanical prophylactic modalities (graduated elastic compression and sequential intermittent compression) were preferred over pharmacologic modalities. These results suggest that implementation of prophylaxis remains underutilized despite published reports, including NIH guidelines. Our results indicate that the majority of surgical patients seen in this suburban hospital have two or more risk factors for developing venous thromboembolism.

Venous thromboembolism prophylaxis and risk assessment in medical patients.

In summary we have developed a VTE risk assessment system for medical patients based on our prior experience in surgical patients. In this model we divide individuals into low, moderate, and high-risk categories. We realize that our system needs further validation with appropriate diagnostic endpoints to correlate the actual occurrence of venous thromboembolism with the predicted risk on the basis of our score system. Nevertheless, the proposed model reflects one approach to achieving a prophylaxis tailored to the patients' risk.

Venous stasis and vein lumen changes during surgery.

The mechanisms underlying the development of postoperative deep vein thrombosis remain to be fully elucidated. Previous studies have suggested that peroperative venous distension may be a factor associated with venous thromboembolism. In this study we have obtained high resolution ultrasound images of gastrocnemius and posterior tibial veins in 62 patients undergoing a range of general surgical procedures. From these we determined the changes in vein diameter occurring during the operative procedures, in response to induction of anaesthesia, and after completion of surgery. Veins showed no evidence of dilatation in response to the induction of anaesthesia, but by the end of the operative procedure showed distension of 22-28 per cent. Distension was most prominent in the gastrocnemius veins, and lesser distension was observed in the posterior tibial veins. In a series of patients who received an infusion of 1 litre of saline in addition to basal requirements, distension was 57 per cent compared with 22 per cent in the corresponding control group. Intraoperative venous distension is associated with factors that lead to deep vein thrombosis and may be involved in the mechanisms which result in the commencement of deep vein thrombosis.

Role of compression modalities in a prophylactic program for deep vein thrombosis.

During the past decade, we have learned a great deal about the etiology, pathogenesis, diagnosis, and treatment of thromboembolic disease. Subcutaneous heparin has emerged as a major deterrent worldwide for thrombosis prevention but is associated with the potential risk of bleeding and cannot be used in certain patient situations. External compression modalities have emerged as major alternate forms of prophylaxis. We have learned that these devices stimulate the fibrinolytic system, prevent stasis and the endothelial injury that can accompany extreme venous distention. Since they are not associated with bleeding or other serious complications, they are attractive methods for most surgeons, including those performing delicate or complex surgical procedures. Independent studies worldwide have demonstrated their effectiveness in reducing deep vein thrombosis, as recognized by the NIH Consensus Development Panel, and the evidence is compelling that DVT efficacy is a valid marker for PE efficacy. Since these devices reduce the incidence of deep vein thrombosis, they almost certainly must prevent pulmonary emboli; however, a properly designed protocol should be conducted to validate these assumptions. Evidence suggests that full-leg sequential compression is superior to calf compression, but further study is necessary. We believe that a hospital-wide plan, including risk-factor assessment and application of clinical management guidelines, including all available modalities, is important to provide the maximum protection of patients with the lowest risk of side effects. Such a program has been very successful in our community.

Regimen for improved effectiveness of intermittent pneumatic compression in deep venous thrombosis prophylaxis.

The incidence of deep venous thrombosis (DVT) was assessed in a series of 78 patients undergoing major surgical operations to compare the prophylactic effectiveness of intermittent sequential pneumatic compression alone with the simultaneous use of graduated compression stockings and intermittent sequential pneumatic compression. The diagnosis of DVT was determined with the I-125 fibrinogen-uptake test, Doppler ultrasound, maximum venous outflow by strain-gauge plethysmography, and contrast venography. The incidence of DVT in nonstockinged legs was 9% while that in the stockinged legs was 1%. The simultaneous use of graduated elastic compression stockings and intermittent pneumatic compression is more effective than pneumatic compression alone in the prevention of postoperative DVT.

Type of compression for reducing venous stasis. A study of lower extremities during inactive recumbency.

Determination of the optimal compression to reduce venous stasis was studied in terms of the amount of pressure and manner of application (graded or uniform pressure). Both lower extremities of seven inactive recumbent subjects were tested using transcutaneous Doppler ultrasonic measurement of femoral vein blood flow velocity. Optimal compression was defined as the externally applied pressure that produced the greatest increase in femoral vein flow velocity consistent with safety and the practicality of hospital use of elastic stockings. Optimal compression for elastic stockings to be used by hospitalized patients who spend substantial time in bed should be 18 to 8 mm Hg (ankle to midthigh). At this compression, average femoral vein blood flow velocity is increased to 138.4% of base line. Gradient compression at this level was found to produce a greater femoral vein flow velocity than the same amount of compression distributed uniformly over the lower extremity.