Postoperative DVT Prophylaxis: Use 81 mg Aspirin Twice Daily, Not 325 mg
For postoperative deep vein thrombosis prophylaxis after joint arthroplasty, aspirin 81 mg twice daily is the appropriate dose—not 325 mg twice daily—as it provides equivalent VTE protection with significantly lower bleeding risk. 1, 2, 3
Evidence-Based Dosing Recommendation
Low-Dose Aspirin (81 mg BID) is Superior
The 81 mg twice daily regimen demonstrates equivalent or superior VTE prevention compared to 325 mg twice daily, with significantly fewer bleeding complications. 1, 2, 3
In a retrospective study of 625 primary joint arthroplasties, 81 mg BID resulted in bleeding rates of only 2.5% compared to 7.6% with 325 mg once daily (p=0.0029), while VTE rates were not significantly different (1.5% vs 2.7%, p=0.41). 1
A large study of 12,866 TKA cases found that 81 mg BID achieved a VTE rate of 0.23% compared to 1.41% with 325 mg BID (p<0.001), demonstrating that lower dose aspirin actually performed better for thromboprophylaxis. 2
Analysis of 5,666 TKA patients showed symptomatic DVT occurred in only 0.3% of patients on 81 mg BID versus 1.4% on 325 mg BID (p=0.0009), with no difference in bleeding complications. 3
Why 325 mg BID Lacks Evidence Support
The American Association of Orthopedic Surgeons recommendation for 325 mg twice daily (650 mg total daily dose) has no supporting evidence from randomized trials. 4
The pivotal PEP trial that established aspirin's efficacy for VTE prophylaxis used only 160 mg total daily dose, not the 650 mg daily dose suggested by some protocols. 4
The AAOS guideline has been criticized for selective literature review that omitted randomized trials demonstrating statistically significant PE reduction with aspirin, resulting in recommendations not linked to their own analysis. 5, 4
Guideline-Supported Approach
American College of Chest Physicians (ACCP) Methodology
The ACCP guidelines are methodologically superior, incorporating only high-quality randomized trial evidence and focusing on patient-important outcomes (mortality, morbidity, quality of life). 5, 4
The ACCP approach considered all evidence from randomized trials using explicit criteria to grade evidence, making their recommendations more reliable than AAOS guidelines. 5
Recommended Regimen
Aspirin 81 mg twice daily for 35 days after hip or knee arthroplasty provides optimal VTE prophylaxis in low-to-moderate risk patients. 4
This duration is based on the PEP trial of 19,000 patients, which demonstrated that 35 days of aspirin reduced VTE risk (RR 0.71,95% CI 0.54-0.94) with only modest bleeding increase (2.9% vs 2.4%, p=0.04). 4
Duration and Timing Considerations
Standard Duration
Continue aspirin for 30-35 days postoperatively for VTE prophylaxis. 4, 6
A study of 9,208 TKA patients found that aside from a single DVT at day 44, all VTE events occurred within 30 days of surgery, validating the 30-day prophylaxis window. 6
The median time to VTE was 8 days (IQR 2-15.5 days), with most events occurring in the first two weeks. 6
Patients on Chronic Aspirin for Cardiovascular Disease
For patients taking aspirin for secondary cardiovascular prevention, continue it indefinitely throughout the perioperative period—do not stop it. 5, 4
The ACCP recommends continuing aspirin perioperatively for patients with prior MI, stroke, coronary stents, or other cardiovascular indications. 4
After the first month post-surgery, aspirin 75-325 mg daily should be continued long-term for cardiovascular prophylaxis. 5
Common Pitfalls to Avoid
Dosing Errors
Do not use 325 mg twice daily (650 mg total daily) as this significantly increases bleeding without improving VTE protection. 1, 2, 3
The 325 mg BID regimen resulted in 3-fold higher bleeding rates (7.6% vs 2.5%) and actually worse VTE outcomes in some studies. 1, 2
Cardiovascular Aspirin Management
For patients on dual antiplatelet therapy (aspirin + P2Y12 inhibitor), continue aspirin but hold the P2Y12 inhibitor before surgery (clopidogrel 5 days, ticagrelor 3-5 days, prasugrel 7 days). 4
Resume aspirin within 24 hours postoperatively once adequate hemostasis is achieved, as maximal antiplatelet effect occurs within minutes. 4
Outdated Practices
Do not hold aspirin for 10 days preoperatively—this outdated practice unnecessarily increases thrombotic risk. 4
If aspirin must be held for high bleeding risk scenarios, 5-7 days is sufficient, as this allows adequate platelet turnover. 4
Special Populations
High Bleeding Risk Patients
For patients at genuinely high bleeding risk who cannot receive any antiplatelet therapy, mechanical prophylaxis with graduated compression stockings and/or intermittent pneumatic compression should be used. 5
However, the recommendation for no pharmacologic prophylaxis in high bleeding risk patients is concerning, as it exposes patients to increased risk of fatal PE. 5
Body Weight Considerations
A retrospective review of 403 hip/knee arthroplasties found that body weight-based aspirin dosing had significantly lower VTE incidence at 42 days (RR 0.31,95% CI 0.12-0.82) and 6 months (RR 0.38,95% CI 0.18-0.80). 5
However, standard 81 mg BID dosing appears effective across BMI categories without need for dose adjustment in most patients. 5