Postoperative prophylactic anticoagulation in flap surgery: A review of the evidence and challenging common beliefs

Authors: Malekzadeh H, Kluemper J, Elemosho A, Janis JE

Affiliation: Dept. of Plastic and Reconstructive Surgery, Ohio State University Wexner Medical Center

Journal: Journal of Reconstructive Microsurgery; published Oct, 2025

PMID: 41072483

Key takeaways

• Across 11 studies, postoperative anticoagulation increased hematoma (5.0% vs 3.0%; OR 2.4) without reducing complete flap failure or reoperation.

• Agent-specific signal: unfractionated heparin (UFH) drove bleeding risk; low–molecular-weight heparin (LMWH) showed no hematoma signal.

• Adding aspirin to LMWH increased reoperations (17.5% vs 10.1%) with no flap-survival benefit.

• Recommendation: employ risk-based prophylaxis instead of routine postoperative anticoagulation for “anastomosis protection.”

Background

Anticoagulants are commonly used after microvascular reconstruction to prevent pedicle thrombosis, but their benefit for flap survival is unproven and practice is highly variable.

Objective

Determine whether prophylactic postoperative anticoagulation improves flap outcomes and quantify agent-specific risks.

Methods

• Design: Systematic review and meta-analysis (Level III evidence base).

• Search window: 1995–January 2025 (PRISMA-compliant).

• Inclusion: Postoperative systemic anticoagulation (UFH/LMWH/other) with a comparator group; outcomes: hematoma, complete flap failure, reoperation. Excluded salvage/therapeutic dosing, <10 cases, or no comparator.

• Studies: 11 total; 7 “anticoagulation vs none” (≈4,858 cases), 4 “LMWH ± aspirin” (≈1,102 cases); mixed head & neck, breast, and other free flaps.

• Statistics: Mantel–Haenszel fixed/random effects by heterogeneity; odds ratios with 95% confidence intervals; sensitivity analyses; subgroup by agent.

Results

• Anticoagulation vs none:

  • Sample size/events reported: ~4,858 cases across 7 studies; flap failure (event number not reported) pooled rates 3.2% (anticoag) vs 5.2% (control).

  • Flap failure: pooled 3.2% (anticoag) vs 5.2% (control); OR 0.82 (95% CI 0.41–1.64; p=0.57; I²=6%).

  • Bleeding: hematoma higher with anticoagulation (≈5.0% vs 3.0%; OR ~2.4), primarily driven by UFH; LMWH not significant for bleeding.

  • Reoperation: no significant difference overall.

• LMWH + aspirin vs LMWH alone:

  • Sample size/events reported: ~1,102 cases across 4 studies; flap failure reported in 3 studies (event number not provided).

  • Flap failure: pooled 2.3% (LMWH+ASA) vs 3.2% (LMWH); OR 0.72 (95% CI 0.27–1.92; p=0.51; I²=0%).

  • Reoperation: higher with aspirin addition (≈17.5% vs 10.1%); inconsistent hematoma signal; no flap-survival benefit.

• VTE context: Some included studies noted venous thromboembolism reduction with prophylaxis—supporting individualized, VTE-focused decisions rather than “flap-protection” dosing.

• Power note for flap failure: Failure events were infrequent (≈2–5%) and only 3–4 studies contributed to the failure analyses; confidence intervals were wide and crossed 1 → underpowered to detect modest differences.

Conclusion

Routine postoperative heparinization increases bleeding without improving flap survival; adding aspirin to LMWH raises reoperations. Adopt individualized, risk-stratified VTE prophylaxis rather than blanket anticoagulation for free flaps.

Strengths & limitations

• Strengths: Contemporary focus on the postoperative window; agent-specific subgrouping (UFH vs LMWH); sensitivity analyses.

• Limitations: All Level III and mostly retrospective; regimen heterogeneity (dose/timing/duration); incomplete adjustment for baseline thrombotic risk and case complexity.

Clinical relevance

• Routine postoperative anticoagulation in average-risk patients does not reduce rates of flap failure, although the results are likely not powered sufficiently. 

• Adding aspirin to LMWH may increase rates of takebacks without a flap survival gain.

• Risk-stratify: Use Caprini score and thrombophilia status to escalate intensity/duration (e.g., extended LMWH) while balancing bleeding risk; document explicit bleed monitoring.