The Role of Flow Couplers in Free Flap Monitoring: Evidence From a Systematic Review and Meta-analysis

Flow couplers (FCs) are increasingly used in microsurgical free tissue transfer to provide continuous, real-time monitoring of venous outflow at the anastomotic site. This systematic review and meta-analysis evaluates the clinical performance of FCs, focusing on diagnostic accuracy and flap outcomes compared with conventional monitoring techniques.

A systematic search of PubMed, Web of Science, and the Cochrane Library was conducted through November 1, 2025, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Clinical studies reporting FC use in free flap reconstruction were included. Data on flap survival, venous thrombosis, complications, and FC diagnostic performance were extracted. Meta-analyses were performed to calculate pooled sensitivity, specificity, and flap failure rates.

Eleven studies including 1775 free flaps (876 monitored with FCs) met inclusion criteria. Pooled sensitivity and specificity for detecting flap compromise were 96.5% and 90.9%, respectively. Flap failure occurred in 2.2% of FC-monitored flaps versus 3.1% in controls. FCs showed a high negative predictive value but variable positive predictive value, with false-positive signal losses being frequently caused by technical issues rather than true thrombosis. False negatives were uncommon. Compared with traditional monitoring methods, FCs provided superior continuous venous assessment.

FCs are highly sensitive tools for early detection of venous compromise in free flap surgery, particularly in buried reconstructions. However, limited specificity and inability to detect arterial insufficiency support the use of multimodal monitoring strategies. Standardized protocols and technical expertise are essential to minimize false positives and optimize flap monitoring outcomes.