The use of low molecular weight heparins for the prevention of postoperative venous thromboembolism in general surgery. A survey of practice in the United States

BACKGROUND

Even though low molecular weight heparins (LMWHs) have become the standard for venous thromboembolism (VTE) prophylaxis in most European countries and Canada, it was not until recently that LMWHs were approved for use in the United States. The main objective of this study was to assess the current preferences and attitudes of United States surgeons toward the prevention of VTE with particular reference to LMWH.

METHODS

A survey with questions relative to VTE awareness, risk factors, and prevention practices was mailed to 10,000 Fellows of the American College of Surgeons.

RESULTS

A total of 1,145 (11.45%) usable questionnaires were returned. The vast majority (96%) of respondents use prophylaxis against VTE. Although LMWHs were rated first regarding efficacy and second regarding simplicity of use, conventional unfractionated heparin at fixed doses remains the preferred pharmacological agent for VTE prevention (74%), followed by 2 LMWHs: enoxaparin (34%) and dalteparin (16%). Overall, 52% of surgeons preferred physical methods over pharmacological methods when used separately and 26% of surgeons utilize combined physical-pharmacological modalities.

CONCLUSIONS

North American general surgeons have substantially modified their approach to VTE prevention in the last 4 years. Physical methods and unfractionated heparin remain the preferred prophylactic modalities, but LMWHs have gained rapid acceptance since their approval for use for VTE prevention in North America. Even though the results of this survey must be interpreted with caution because of the limited response rate and possible sampling bias, they still reflect the current preferences and attitudes of North American surgeons toward prophylaxis.

Home use of impulse compression of the foot and compression stockings in the treatment of chronic venous insufficiency

PURPOSE

The use of intermittent pneumatic compression, in addition to elastic bandages or stockings, accelerates the healing of leg ulcers in patients with severe chronic venous insufficiency (CVI). There is recent evidence that impulse compression of the plantar venous plexus reduces post-traumatic ankle swelling and prevents postoperative venous thromboembolism. The purpose of this study was to evaluate the clinical and hemodynamic responses after home use of impulse foot compression for 3 months in patients already using therapeutic compression stockings for the management of CVI.

METHODS

Twelve extremities from 9 patients with documented CVI, class 4 to 5 according to the Clinical, Etiology, Anatomy, Pathophysiology classification system, were included in this prospective cohort study. All patients were instructed to use a foot pump device at home for 2 hours a day for 3 months in addition to therapeutic compression stockings (30-40 mm Hg) worn during the day. The device was set to three cycles (3 seconds) of compression (120 mm Hg) per minute. A clinical scoring system was completed before foot compression and 1, 2, and 3 months thereafter. In addition, all patients underwent air plethysmography studies at the same time intervals, including venous volume, venous filling index, ejection fraction, and residual volume fraction.

RESULTS

Patients reported significant improvement in their scores for swelling (P <.05) and pain (P <.04). Air plethysmography showed a reduction in venous volume and venous filling index, although these differences were not significant. Ejection fraction remained unchanged and residual volume fraction was significantly reduced (P <.05) compared with baseline. The foot compression devices were well tolerated by all the patients in the study.

CONCLUSIONS

The use of home foot impulse compression plus elastic stockings significantly reduced the residual volume fraction as measured by air-plethysmography in a group of patients with severe CVI. This favorable hemodynamic response could, in part, explain the clinical improvement achieved by this combined treatment. However, this represents a preliminary pilot study that needs to be confirmed in future randomized controlled studies with more patients included.

Effective risk stratification of surgical and nonsurgical patients for venous thromboembolic disease

Effective and safe methods of preventing venous thromboembolism (VTE) are now widely available, but a significant proportion of patients develop VTE either because thromboprophylaxis has not been used or because the intensity of thromboprophylaxis is not matched to the level of risk. Thromboembolic risk varies widely according to the clinical setting and presence of underlying risk factors, but VTE may not be suspected even in high-risk patients. Clinical risk factors for VTE include recent surgery, cancer, stroke, previous VTE, immobilization, and advanced age. Recent attention has focused on the role of inherited and acquired molecular factors in determining overall thromboembolic risk. These factors include the classic thrombophilias-deficiencies of antithrombin III, protein C, and protein S-and several newly described molecular risk factors: factor V Leiden, the prothrombin 20210A gene mutation, and hyperhomocysteinemia. Based on emerging knowledge of risk factors, several risk assessment models (RAMs) have been devised that stratify patients according to overall VTE risk, allowing thromboprophylaxis to be tailored appropriately. Compared with older risk assessment formulas, current RAMs are simpler and include specific recommendations for thromboprophylaxis based on the available scientific evidence. Consensus documents on VTE prevention classify patients into low-, moderate-, and high-risk categories. More recently, a new risk group, very high risk, has been described. Very-high-risk patients are especially prone to thromboembolic complications and need intensive and in some cases prolonged thromboprophylaxis.

Finding the right fit: effective thrombosis risk stratification in orthopedic patients

Patients undergoing orthopedic surgery are at increased risk of venous thromboembolic events. Proven prophylactic measures are available but are generally underused. However, even one of the most effective therapies available, low-molecular-weight heparin, fails to prevent deep vein thrombosis in approximately 15% of patients undergoing total hip replacement. Clinical outcomes and cost-effectiveness of venous thromboembolism prophylaxis may be optimized by tailoring the treatment to the level of risk of each patient. Overall thromboembolic risk depends on the interactions among multiple factors, such as those that relate to the current clinical status and underlying susceptibility of the patient. Presently, risk assessment models that consider these factors may be of practical assistance in stratifying patients. Improving identification of patients with additional risk factors is a goal of future models. Novel therapies, such as the recombinant hirudin desirudin, or strategies, such as prolonged postoperative prophylaxis, may provide improved protection in these patients and should be considered in the future.

Risk factor assessment in the management of patients with suspected deep venous thrombosis

BACKGROUND

To evaluate the prevalence of thrombosis risk factors in a group of patients undergoing venous duplex scanning (VDS) and to design a risk factor stratification model with the ability to improve the diagnostic yield of VDS.

METHODS

Risk factor assessment and VDS were performed on 1,000 patients with clinically suspected lower extremity deep vein thrombosis (DVT) and patients were divided into two groups based upon the outcome of their scan: those with and those without confirmed DVT. Univariate and multivariate logistic regression analyses were performed in order to determine the significance of each risk factor in relation to having a confirmed DVT.

RESULTS

There were 181 patients (18.1%) with confirmed DVT. A prior history of DVT/pulmonary embolism, malignancy, prior immobilization, and age over 70 were the most important risk factors associated with having a DVT confirmed on VDS. A novel risk factor stratification model was created utilizing the odds ratios of those factors found to be significant and the prevalence of DVT was found to be 92.4% in the high risk category, 11.5% in the moderate risk category, and 3.2% in the low risk category using this model.

CONCLUSIONS

Venous duplex scanning is established as the screening test of choice when one suspects the diagnosis of DVT despite the significant cost of performing and interpreting the test. We suggest that a better clinical model utilizing risk factor assessment may be the key to increasing the yield rate and cost-effectiveness of VDS by excluding low-risk patients from undergoing unnecessary testing.

The influence of oral anticoagulation therapy on deep vein thrombosis rates four weeks after total hip replacement

PURPOSE

The purpose of this study was to assess the rate of postoperative deep vein thrombosis (DVT) as a function of oral anticoagulation therapy after total hip replacement surgery.

METHODS

A total of 125 patients completed the study. All the patients received sequential gradient pneumatic compression over elastic stockings until hospital discharge. In addition, all the patients underwent postoperative heparin therapy followed by oral warfarin therapy, adjusted in dose to maintain a goal international normalized ratio (INR) level of 2.0 to 3.0. Warfarin therapy and compression stockings were continued for 1 month after surgery. Bilateral duplex scanning was performed 1 and 4 weeks after surgery to assess the rate of DVT.

RESULTS

Nineteen of the 125 patients had DVT develop (15.2%). Of those thromboses, six (31.6%) and 13 (68%) were detected 1 week and 1 month after surgery, respectively. The rate of proximal DVT was 2.4% (3 of 125) 1 week after surgery and rose to 8.2% (10 of 122) 1 month after surgery. Most DVT cases (64%; 12 of 19) were asymptomatic. The patients in whom DVT developed had significantly lower INR values during the second to fourth postoperative weeks than did those patients without thrombosis, and no differences in INR values were found during the first postoperative week.

CONCLUSION

The risk of the development of DVT extends beyond hospital discharge in patients who undergo total hip replacement, despite a regimen of prolonged oral anticoagulation therapy. This is particularly true in patients whose INR values did not reach therapeutic range during the first postoperative month. Therefore, thrombosis prophylaxis regimens on the basis of the administration of warfarin should try to maintain INR values within therapeutic range during the entire first postoperative month to minimize the incidence of DVT.

Deep vein thrombosis outcome and the level of oral anticoagulation therapy

OBJECTIVE

The purpose of this study was to assess the rate of deep vein thrombosis (DVT) resolution and DVT outcomes as functions of the level of oral anticoagulation therapy achieved with warfarin.

METHODS

In 33 consecutive patients, a series of 35 limbs with acute symptomatic DVT was followed throughout 1 year of anticoagulation therapy. All the patients underwent 5 days of intravenous unfractionated sodium heparin therapy that was adjusted in dose to prolong the activated thromboplastin time to 2.0 to 2.5 times the control. In addition, warfarin was administered for a period of 6 months, with a target international normalized ratio (INR) between 2.0 and 3.0. All the patients underwent venous duplex scanning and physical examination at the time of diagnosis and at 1 week, 1 month, 3 months, 6 months, and 1 year.

RESULTS

At the end of the 1-year study period, the rate of complete DVT resolution was 68%. The median INR values in patients with complete DVT resolution were significantly higher than those of patients with incomplete DVT resolution after 1, 3, and 6 months of treatment with warfarin. In addition, the proportion of patients with INR values below therapeutic range was significantly higher in patients with incomplete DVT resolution than in patients with complete DVT resolution after 1, 3, and 6 months of treatment with warfarin. The presence of occlusive thrombi was associated with incomplete DVT resolution. Of the patients with occlusive thrombi, 62% had chronic venous insufficiency symptoms develop, whereas only 11% of the patients with nonocclusive thrombi (P =.003) had these symptoms develop.

CONCLUSION

Despite 6 months of oral anticoagulant therapy, almost one third of thrombi did not resolve completely. The INR values were significantly higher in those patients with complete DVT resolution. These results suggest that the maintenance of an INR level between 2.0 and 3.0 throughout oral anticoagulation therapy will minimize the rate of incomplete DVT resolution.

Matching risk with treatment strategies in deep vein thrombosis management

Successful and cost-effective prophylaxis against venous thromboembolism (VTE) depends on the availability of safe and effective antithrombotic methods, and the ability to match these to patients according to their level of thromboembolic risk. The last 20 years have seen significant developments in methods of thromboprophylaxis but, despite use of the best available methods, VTE still occurs in a significant proportion of patients. Efforts are now focused both on developing more effective pharmacological and physical methods, and improving assessment of thromboembolic risk in clinical practice, with the goal of avoiding unnecessary prophylaxis in low-risk patients and providing enhanced protection to high-risk patients. Factors known to exert a direct effect on thromboembolic risk include previous VTE, advancing age, surgery, malignancy, immobility, and the presence of thrombophilic states. Other less well-defined risk factors include obesity, pregnancy, and leg varicosities. Various risk assessment models (RAMs) have been devised based on these factors, but most of the resulting risk assessment formulae, some of them based on laboratory test results, have been too complicated to gain acceptance in routine clinical practice. Reflecting the need to refine the use of thromboprophylaxis in clinical practice, a number of RAMs have been developed recently, based on epidemiological evidence. Some models include specific recommendations for prophylaxis, based on evidence from randomized, controlled trials.

Evaluation of therapeutic compression stockings in the treatment of chronic venous insufficiency

BACKGROUND

Chronic venous insufficiency (CVI) affects a significant portion of the world's population, causing substantial morbidity and medical expenditure. Its pathophysiology is based on venous hypertension in the lower extremities, with vascular compression therapy remaining the foundation of its medical management.

OBJECTIVE

To evaluate the effectiveness of therapeutic compression stockings in the treatment of lower extremity CVI.

METHODS

A group of 112 patients with CVI received graduated-compression stockings and rated the severity of their symptoms on a five-point scale before wearing the stockings, and then again after 1 and 16 months of treatment. Patient complaints associated with stocking use and patient compliance rates were also recorded at 1 and 16 months.

RESULTS

A statistically significant improvement (p < 0.001) was reported in patient severity scores for lower extremity swelling, pain, skin discoloration, activity tolerance, depression and sleeping problems after 1 and 16 months of treatment with compression stockings.

CONCLUSION

Therapeutic graduated-compression stockings are an effective treatment for CVI of the lower extremities.

Venous duplex imaging follow-up of acute symptomatic deep vein thrombosis of the leg

PURPOSE

The purpose of this study was to evaluate the rate of resolution of deep vein thrombosis (DVT) in the leg, by means of duplex imaging, in patients with symptoms during a 6-month period after initial diagnosis.

METHODS

Seventy-three limbs in 69 patients with acute DVT diagnosed by duplex imaging received conventional heparin and warfarin treatment and underwent subsequent duplex studies 1, 4, 12, and 24 weeks after the initial diagnosis. The objectives of the study were to document (1) the rate or complete resolution of DVT, (2) the proportion of unstable, floating thrombi, and (3) the development of chronic damage as a result of vessel wall scarring.

RESULTS

The rate of normalization of DVT 6 months after diagnosis was 78% in the common femoral vein, 70% in the superficial femoral vein, 75% in the popliteal vein, and 70% in the calf veins examined at the scheduled intervals. Twenty-six percent of thrombi were considered unstable on the baseline examination. The average number of days necessary for these thrombi to become stable was 10.7 days. Damage to the vessel wall or valves was documented in 44% of the patients.

CONCLUSIONS

Rates of resolution of DVT were similar for the different veins of the leg studied. There was a high proportion of unstable thrombi, which present a high potential risk of embolization. Serial duplex scanning after DVT renders important information with regard to thrombus resolution, propagation, and attachment to the vein wall.