Prevention of venous thromboembolism in the orthopedic surgery patient

Nearly half of orthopedic surgery patients do not receive appropriate prophylaxis for venous thromboembolism (VTE), as defined by American College of Chest Physicians (ACCP) consensus guidelines, according to a recent analysis of a nationwide database of hospital admissions.¹ Even in teaching hospitals, compliance with consensus guidelines for thromboprophylaxis is suboptimal. In a study of adherence to the ACCP guidelines for VTE prevention among 1,907 surgical patients at 10 teaching hospitals, only 45.2% of hip fracture patients received optimal VTE prophylaxis.² Rates of optimal prophylaxis were higher among patients undergoing hip arthroplasty and knee arthroplasty—84.3% and 75.9%, respectively—but were still in need of improvement.²

GROWING INTEREST IN POSTOPERATIVE VTE PROPHYLAXIS AS A QUALITY INDICATOR

As noted in the introductory article in this supplement, the Joint Commission on Accreditation of Healthcare Organizations has taken notice of these shortcomings and has proposed national consensus standards for VTE prevention and treatment.³ Among its proposed standards are two related to risk assessment and prophylaxis: whether risk assessment/prophylaxis is ordered within 24 hours of hospital admission and within 24 hours of transfer to the intensive care unit.

Other quality-monitoring initiatives are focused specifically on VTE in the surgical population. The Surgical Care Improvement Project (SCIP) has approved two quality measures with respect to VTE prevention: (1) the proportion of surgical patients for whom recommended VTE prophylaxis is ordered, and (2) the proportion of patients who receive appropriate VTE prophylaxis (based on ACCP guideline recommendations) within 24 hours before or after surgery.⁴

In the future, two other VTE-related quality measures from SCIP may be implemented by the Centers for Medicare and Medicaid Services: (1) how often intra- or postoperative pulmonary embolism (PE) is diagnosed during the index hospitalization and within 30 days of surgery, and (2) how often intra- or postoperative deep vein thrombosis (DVT) is diagnosed during the index hospitalization and within 30 days of surgery.⁵

VTE RISK IN ORTHOPEDIC SURGERY

Surgical patients can be stratified into four VTE risk levels—low, moderate, high, and highest—based on age, surgery type, surgery duration, duration of immobilization, and other risk factors.⁶ For patients undergoing orthopedic surgery, these levels may be defined according to the following patient and surgical characteristics:

• Low risk—surgery duration of less than 30 minutes, age less than 40 years, repair of small fractures
• Moderate risk—age of 40 to 60 years, arthroscopy or repair of lower leg fractures, postoperative plaster cast
• High risk—age greater than 60 years, or age 40 to 60 years with additional VTE risk factors, or immobilization for greater than 4 days
• Highest risk—hip or knee arthroplasty, hip fracture repair, repair of open lower leg fractures, major trauma or spinal cord injury, or multiple risk factors for VTE (age > 40 years, prior VTE, cancer, or hypercoagulable state).

For patients in the low-risk category, no specific prophylaxis is indicated beyond early and aggressive ambulation.⁶ For those in all other risk categories, prophylaxis with pharmacologic anticoagulant agents and/or mechanical devices is indicated, as reviewed below.

All major orthopedic procedures confer highest risk level

Notably, the “highest risk” category includes any patient undergoing hip or knee arthroplasty or hip fracture repair. Among orthopedic surgery patients in this highest-risk category, rates of VTE events in the absence of prophylaxis are as follows:⁶

• Calf DVT, 40% to 80%
• Proximal DVT, 10% to 20%
• Clinical PE, 4% to 10%
• Fatal PE, 0.2% to 5%.

Hip replacement poses greater risk than knee replacement

Within this overall highest-risk category, thromboembolic risk in the absence of prophylaxis differs among procedures. Although patients undergoing hip replacement and those undergoing knee replacement have similar rates of DVT of any type,^6,7 hip replacement is associated with higher rates of the more clinically important events, specifically proximal DVT and PE. In the absence of prophylaxis, proximal DVT occurs in 23% to 36% of hip replacement patients as opposed to 9% to 20% of knee replacement patients; similarly, PE occurs in 0.7% to 30% of hip replacement patients as compared with 1.8% to 7.0% of knee replacement patients.^6,7

What about bleeding risk?

For many orthopedic surgeons, the risk of bleeding as a result of anticoagulant prophylaxis of VTE looms larger than the risk of VTE itself. This is likely because bleeding, when it does occur, is likely to occur more acutely than VTE does and may directly compromise the result of the operation. For this reason, orthopedic surgeons may be more likely to actually witness bleeding events than VTE events (especially fatal PEs) while their patients are still under their care, leading to a misperception of the relative risks of anticoagulation-related bleeding and thromboembolism.

In reality, rates of major bleeding with pharmacologic prophylaxis of VTE are a tiny fraction of the above-listed rates of VTE events in the absence of prophylaxis in patients undergoing major orthopedic surgery. Reported 30-day rates of major bleeding in patients receiving VTE prophylaxis with heparins range from 0.2% to 1.7%; these rates barely differ from the rates among placebo recipients in the same VTE prophylaxis trials, which range from 0.2% to 1.5%^.8,9 Additionally, within the continuum of risk of major bleeding from various medical interventions, VTE prophylaxis with heparins is one of the lowest-risk interventions, posing far less risk than, for example, the use of warfarin in ischemic stroke patients or in patients older than 75 years.