Introduction: Early recognition of vascular compromise is associated with improved rates of free flap salvage. The implantable Cook-Swartz Doppler probe is most commonly placed at the arterial anastomosis, despite the fact that venous thrombosis is the most common cause of vascular compromise in free flap reconstruction. The venous anastomotic flow coupler combines a venous anastomotic coupler and implantable Doppler probe to assess venous patency at the anastomotic site; few studies have been conducted on its utility in head and neck free flaps.
Objective: To describe the accuracy and reliability of the venous flow coupler in postoperative monitoring of head and neck free flaps, compare findings to an implantable arterial Doppler probe, and trend performance over time.
Study design: Retrospective single-institution study
Methods: Both the venous flow coupler and implantable arterial Doppler probe were employed in 89 consecutive patients undergoing head and neck free flap reconstruction from April 2015 to August 2016. Positive Doppler events were defined as loss of arterial or venous signal. All flaps were also evaluated by scheduled physical exam (pin-prick) to identify false-negatives and to determine whether signal loss was a true positive (necessitating return to operating room) or a false positive. Sensitivity, specificity, false-positive rate (FPR), and false-negative rate (FNR) for each device were recorded to compare reliability. The association between increased flow coupler usage and performance was also analyzed.
Results: Nine patients (10.1%) required OR takeback, 8 due to venous thrombosis and 1 due to arterial thrombosis. Permanent signal loss (PSL) occurred in the flow coupler in all 9 takebacks; PSL occurred in the arterial Doppler only in the single case of arterial thrombosis. For the flow coupler, sensitivity was 100%, specificity 81.1%, FPR 18.9%, and FNR 0.0%. For the arterial probe, sensitivity for microvascular compromise was 11.1%, specificity 97.3%, FPR 2.7%, and FNR 88.9%. There was a statistically significant trend towards decreased false-positive events with increased flow coupler usage (p=0.008). Flap salvage rate for flow coupler events was 7/9 (77.8%), and for arterial Doppler events was 0/1 (0.0%). No patients were returned to OR with findings of normal microvascular flow.
Conclusion: The flow coupler has very high sensitivity in identifying vascular compromise compared to the arterial Doppler probe, particularly in cases of venous thrombosis resulting in an excellent salvage rate of compromised free flaps. There is a moderate FPR, but this decreases significantly with increased usage and, when supplemented with proper physical examination, does not lead to unnecessary OR takebacks. The flow coupler can be a valuable tool in postoperative monitoring of head and neck free flaps.