Prevention of fatal pulmonary embolism with warfarin after total hip replacement

Cost-Effectiveness of Venous Thromboembolism Prophylaxis after Total Hip Replacement

Objective:

To determine the cost-effectiveness of three strategies used for the prevention of venous thromboem-bolism (VTE) in patients undergoing total hip replace-ment (THR), and to perform a sensitivity analysis comparing VTE rates based on different methods of detection.

Methods:

In this cost-effectiveness analysis, three strategies of prophylaxis of postoperative VTE and THR were compared: (1) low-molecular-weight heparin (LMWH); Enoxaparin, (2) warfarin and (3) a combination of warfarin, heparin (UFH), graduated stockings and sequential long-leg pneumatic compression devices. The model estimates were based on pooled data from the published literature and from personal data in our series of hip replacement patients. Expected direct costs of VTE care, including prophylaxis, diagnosis and manage-ment of thromboembolic and hemorrhagic complications, were estimated for a hypothetical cohort of 100 patients in 2001 US dollars from data available for patients hospitalized at Evanston Northwestern Health-care. A sensitivity analysis was performed with different rates of VTE based on routine venography, routine duplex ultrasound, or selective diagnosis and treatment of symptomatic patients.

Results:

When venography was used to diagnose VTE, the cost of warfarin or LMWH treatment was $118 422 and $104 732 per 100 patients, respectively, providing cost savings of $ 13 690 per hundred patients for LMWH. When VTE rates were based on duplex ultrasound diagnoses, LMWH resulted in cost savings of $4602 and $1345 per 100 patients compared with the use of warfarin or the combined approach, respectively. However, when the rates of VTE were based on confirmed symptomatic cases, the use of LMWH resulted in an increased cost of $4486 and $10015 per 100 patients compared with warfarin and the combined approach, respectively.

Conclusions:

The use of LMWH for the prevention of VTE after THR was more cost-effective than using warfarin or the combined approach, when the VTE rate was based on routine venography or duplex ultrasound. However, the combined approach was more cost-effective than the use of warfarin or LMWH alone when only patients with confirmed, symptomatic VTE were treated.

Investment in prolonged thromboprophylaxis with dalteparin improves clinical outcomes after hip replacement

Clinical guidelines recommend the use of extended out-of-hospital thromboprophylaxis in patients who have had major arthroplasty. However, the cost-effectiveness of prolonging pharmacological thromboprophylaxis into the out-of-hospital phase following hip replacement surgery remains the subject of considerable debate. This debate centers on the clinical relevance of the 'surrogate' venographic endpoints that have been used in most clinical trials and used to generate some of the cost analyses of thromboprophylaxis. The objective of this study was to estimate, from the payer perspective, the direct medical costs of prolonging the duration of thromboprophylaxis with dalteparin from 1 week to 28-35 days in patients undergoing hip replacement, and to compare these to the costs associated with using 'standard' in-hospital thromboprophylaxis with low-molecular-weight heparin (LMWH) or warfarin. To derive 'best' estimates for rates of clinically and economically relevant thromboembolism associated with hip replacement surgery (i.e. those that would in reality incur management costs), we used data on the prevalence of both symptomatic and asymptomatic deep vein thrombosis (DVT) and pulmonary embolism (PE). These estimates were used in conjunction with diagnostic-related groups (DRG) reimbursement rates and a dalteparin cost model, which assumed home-based self-administration for prolonged thromboprophylaxis, to calculate overall direct medical costs of prolonged vs. in-hospital thromboprophylaxis. The management costs of the strategies evaluated were, to the nearest 1000 Euros: 465 000 Euros for in-hospital prophylaxis with LMWH; 339 000 Euros for in-hospital prophylaxis with warfarin; and 368 000 Euros for prolonged prophylaxis with dalteparin. For every 1000 patients treated, prolonging thromboprophylaxis with dalteparin from 1 to 4-5 weeks will avoid 30 clinical DVTs and 18 PEs at a saving of 2000 Euros per clinical event. Compared with in-hospital warfarin, prolonged thromboprophylaxis with dalteparin will avoid 28 DVTs and four PEs at an incremental cost-effectiveness ratio of 900 Euros per clinical event avoided. We consider that investment in prolonged thromboprophylaxis with dalteparin is justified for the improvement in clinical outcomes produced.

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.