What is the role of Aspirin (Acetylsalicylic Acid) for post-operative prophylaxis?

Aspirin for Post-Operative VTE Prophylaxis

Aspirin is NOT recommended as routine post-operative VTE prophylaxis in most surgical settings, with the notable exception of major orthopedic surgery (hip/knee arthroplasty, hip fracture) where low-dose aspirin (81-325 mg daily) is an acceptable alternative when LMWH or other anticoagulants are contraindicated or unavailable. 1

Evidence-Based Recommendations by Surgical Context

Non-Orthopedic Surgery

• The American College of Chest Physicians (ACCP) explicitly advises AGAINST using aspirin as the sole method of thromboprophylaxis in non-orthopedic surgical patients (Grade A recommendation). 1
• Aspirin should only be considered in non-orthopedic surgery when LDUH and LMWH are contraindicated or unavailable—it is not a first-line option. 1
• The rationale: there are no studies of low-dose aspirin in non-orthopedic surgical patients, and the evidence from orthopedic surgery may not be applicable to other surgical populations. 1

Major Orthopedic Surgery (Hip/Knee Arthroplasty, Hip Fracture)

• Low-dose aspirin (160 mg daily) reduces symptomatic DVT by 28% (RR 0.72,95% CI 0.53-0.96) and fatal PE by 58% (RR 0.42,95% CI 0.25-0.72) compared to placebo in orthopedic patients. 1
• The PEP trial (17,000+ patients) demonstrated these benefits with aspirin 160 mg daily for 35 days starting pre-operatively. 1
• Aspirin causes significantly less operative site bleeding than LMWH, VKA, or fondaparinux (relative bleeding risks: VKA 4.9x, LMWH 6.4x, pentasaccharides 4.2x higher than aspirin). 2
• Recent meta-analyses show aspirin has similar VTE prevention efficacy to other anticoagulants in orthopedic surgery, with no significant difference in mortality or wound complications. 3, 4

Dosing specifics for orthopedic surgery:

• Low-dose aspirin 81 mg twice daily is as effective as standard-dose 325 mg twice daily for VTE prevention after THA, with no difference in bleeding or mortality. 5
• Duration: Continue for 4-6 weeks post-operatively (up to 35 days based on trial data). 1, 5

Knee Arthroscopy

• Thromboprophylaxis with aspirin is only advised when concomitant risk factors are present (Grade A-B recommendation). 1
• Simple knee arthroscopy has low thrombotic risk (9% asymptomatic DVT, 3% proximal DVT), so routine prophylaxis is not indicated. 1

Vascular Surgery

• Aspirin prophylaxis may be considered following vascular surgery, particularly for arterial thrombosis prevention. 1
• For PTA/PTAS procedures: aspirin 325 mg daily should be continued indefinitely post-procedure (combined with clopidogrel for first 4 weeks). 1, 6

Critical Caveats and Contraindications

When Aspirin Should NOT Be Used

• Patients with elevated PE risk: Aspirin is not recommended when there is specifically high risk for pulmonary embolism. 1
• Active bleeding: Aspirin must be withheld until bleeding is controlled. 1
• High VTE risk with high bleeding risk: Use mechanical prophylaxis (IPC) instead of any pharmacologic agent. 7
• Patients already on dual antiplatelet therapy (DAPT): Adding anticoagulation to DAPT significantly increases bleeding risk; use mechanical prophylaxis instead. 7

Comparative Effectiveness

• LMWH and other anticoagulants are MORE effective than aspirin for preventing asymptomatic DVT detected by venography. 1
• Heparins reduce PE risk by approximately two-thirds, while aspirin reduces it by about one-half. 7
• However, aspirin has never been evaluated in RCTs for preventing asymptomatic DVT using venography as an endpoint. 1

Practical Implementation Algorithm

For post-operative VTE prophylaxis, follow this decision pathway:

1. Determine surgical type:

   • Major orthopedic (THA/TKA/HFS) → Proceed to step 2
   • Non-orthopedic → Do not use aspirin as first-line; use LMWH/LDUH unless contraindicated 1

2. For orthopedic surgery, assess bleeding risk:

   • Standard bleeding risk → LMWH preferred over aspirin 1
   • High bleeding risk OR LMWH contraindicated → Aspirin 81-160 mg twice daily acceptable 1, 5

3. Check for contraindications:

   • Active bleeding → Withhold aspirin 1
   • Already on DAPT → Use mechanical prophylaxis only 7
   • Peptic ulcer disease or aspirin intolerance → Use alternative agent 5

4. Duration:

   • Continue aspirin for 4-6 weeks (up to 35 days) post-operatively 1, 5
   • Extended prophylaxis reduces VTE episodes 4

Special Populations

Patients with Myeloproliferative Neoplasms

• Aspirin should be withheld until bleeding is controlled in ET patients with elevated platelet counts. 1
• Prophylaxis with aspirin may be considered following vascular surgery in this population. 1

COVID-19 Patients

• Guidelines specifically recommend against using aspirin for VTE prevention in critically ill COVID-19 patients. 1
• Post-discharge aspirin can be considered as an alternative to LMWH/DOACs for low-risk patients after orthopedic-type procedures. 1

Lower Extremity Injuries

• For isolated lower extremity injuries with/without immobilization, ACCP advises against routine prophylaxis (Grade 1A). 1
• If risk factors present, LMWH preferred over aspirin. 1