Is 81 mg twice daily (bid) of aspirin (acetylsalicylic acid) sufficient for post-operative venous thromboembolism (VTE) prophylaxis after hip surgery?

Aspirin 81 mg Twice Daily for Post-Operative VTE Prophylaxis After Hip Surgery

Aspirin 81 mg twice daily is appropriate for post-operative venous thromboembolism (VTE) prophylaxis after hip surgery in most patients, as it provides adequate protection while minimizing bleeding risk compared to higher doses or other anticoagulants. 1, 2

Evidence for Aspirin in Post-Operative VTE Prophylaxis

Efficacy of Low-Dose Aspirin

• A 2023 study specifically comparing aspirin dosing regimens found that 81 mg twice daily was associated with a lower rate of bleeding complications (2.5%) compared to 325 mg once daily (7.6%), while maintaining comparable VTE prevention efficacy 1
• The 2024 European Society of Cardiology working group statement indicates that aspirin 81 mg twice daily is effective for post-operative VTE prophylaxis after hip arthroplasty, with no difference in efficacy compared to other regimens 2
• Multiple studies have demonstrated that aspirin is non-inferior to other anticoagulants for VTE prophylaxis after major orthopedic surgery 3, 4

Dosing Considerations

• While the American College of Chest Physicians (ACCP) historically recommended aspirin at doses of 160-325 mg daily for VTE prophylaxis 2, more recent evidence supports the lower twice-daily dosing of 81 mg
• The 2018 NEJM study demonstrated that aspirin 81 mg daily was non-inferior to rivaroxaban for extended VTE prophylaxis after initial 5-day rivaroxaban course following hip or knee arthroplasty 3
• The European Society of Cardiology working group specifically noted that patients receiving 81 mg aspirin twice daily after hip arthroplasty had effective VTE prevention regardless of body weight 2

Safety Profile

• Low-dose aspirin (81 mg twice daily) has been associated with significantly fewer bleeding complications compared to higher doses:
  • Lower rates of bleeding (2.5% vs 7.6%, p=0.0029)
  • Fewer suture reactions (1.2% vs 3.3%, p=0.010) 1
• A 2020 meta-analysis of randomized clinical trials found no significant difference in the risk of adverse events, including major bleeding, wound hematoma, and wound infection, between aspirin and other anticoagulants 4

Clinical Algorithm for Post-Hip Surgery VTE Prophylaxis

1. First-line prophylaxis for most patients:

   • Aspirin 81 mg twice daily for 30 days after total hip arthroplasty 2, 1
   • Start within 24 hours post-operatively when hemostasis is achieved

2. Patient factors requiring alternative anticoagulation:

   • History of previous VTE
   • Known thrombophilia
   • Active cancer
   • Prolonged immobility
   • Multiple concurrent VTE risk factors

3. Duration of prophylaxis:

   • Continue for 30 days after total hip arthroplasty 3
   • For hip fracture surgery, consider extending to 35 days 2

Important Considerations and Caveats

• Aspirin should not be used as sole prophylaxis in patients with very high VTE risk (previous VTE, known thrombophilia) 5
• Consider mechanical prophylaxis (intermittent pneumatic compression) in addition to aspirin for higher-risk patients 5
• Renal function does not affect aspirin dosing, unlike many anticoagulants that require dose adjustment 2
• Avoid aspirin in patients with history of aspirin allergy, active peptic ulcer disease, or recent intracranial bleeding 2

In conclusion, aspirin 81 mg twice daily represents an effective, safe, and cost-effective option for VTE prophylaxis after hip surgery for most patients. This regimen balances the need for adequate thromboprophylaxis with minimized bleeding risk.