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, Oct 2025

PMID: 41072483

Key takeaways

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

• Subgroup analyses showed that only unfractionated heparin (UFH) was associated with increased hematoma formation; low–molecular-weight heparin (LMWH) showed no significant effect on hematoma rate.

• Adding aspirin to LMWH increased rates of reoperations (≈17.5% vs 10.1%) with no flap-survival benefit compared to LMWH alone

• Empiric usage of routine anticoagulation may not benefit all patients, however, employing a risk-based approach to postoperative anticoagulant use is warranted especially in those patients at high risk for thrombosis.

  
  

Background

Anticoagulants are commonly used after microvascular reconstruction as a method to prevent microvascular thrombosis and ultimately improve flap survival, but their benefit for flap outcomes is unproven, leading to high variance in clinical practice among microsurgeons.

Objective

The review sought to determine whether prophylactic postoperative anticoagulant use improves flap outcomes.

Methods

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

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

• Inclusion Criteria: Studies comparing postoperative prophylactic use of anticoagulants (UFH/LMWH/DOAC/Vit K antagonists) with a comparator group and reported at least 1 primary outcome; Primary outcomes included hematoma formation, complete flap failure, need for reoperation.

• Exclusion Criteria: anticoagulation use for flap salvage, therapeutic dosing of anticoagulant, studies with <10 cases, or those with no control or comparator group.

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

• Statistical Analysis: Mantel–Haenszel fixed effects model used in studies without substantial heterogeneity; In studies with substantial heterogeneity, a sensitivity analysis was performed and random effects model used. Heterogeneity calculated by using Q test and I² statistics (>50% considered substantial heterogeneity). Results reported as odds ratios with 95% confidence intervals; subgroup analysis by agent.

Results

• Anticoagulation vs none:

  • Sample size/events reported: ~4,858 cases across 7 studies

  • Flap failure: pooled 3.2% (anticoag) vs 5.2% (control); OR 0.82 (95% CI 0.41–1.64; p=0.57; I²=6%). No significant difference overall.

  • Bleeding: pooled 5.0% (anticoag) vs 3.0% (control); OR 2.44 (95% CI: 1.11-5.40; p=0.0.03; I²=65%). Hematoma rates higher with anticoagulation.

    • Subgroup analysis by agent shows this was primarily driven by UFH; LMWH use was not significantly associated with increased hematoma formation.

  • Reoperation: pooled 6.3% (anticoag) vs 4.9% (control); OR 2.90 (95% CI: 0.91 – 9.20; p = 0.07; I² = 77%). 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, reoperation reported in 3 studies, hematoma reported in 4 studies (3 with LMWH)

  • Hematoma:  pooled 6.8% (LMWH) vs 9.2% (LMWH+ASA); OR 0.64 (95% CI 0.37–1.11; p=0.11; I²=48%). No significant differences between groups.

  • Flap failure: pooled 3.2% (LMWH) vs 2.3% (LMWH+ASA); OR 0.72 (95% CI 0.27–1.92; p=0.51; I²=0%). No significant differences between groups.

  • Reoperation: pooled 10.1% (LMWH) vs 17.5% (LMWH+ASA); OR 0.39 (95% CI 0.19–0.79; p=0.01; I²=0%). Reoperation rates significantly higher in patients receiving LMWH+ASA vs LMWH alone.

• 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 studies were Level of Evidence 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.

Bottom line: For most free-flap patients, skip routine postoperative heparin (and avoid LMWH+aspirin combinations). Risk-stratify for VTE and reserve intensified anticoagulation for patients with elevated risk factors while closely monitoring for bleeding.