Could Periodic Laser Doppler Imaging Monitoring Enhance Insights Into Perfusion Challenges in Anterolateral Thigh Flaps? A 5-Year Retrospective Analysis

Background: Postoperative monitoring after free flap transfer is challenging, and clinical observation alone remains subjective and unquantifiable. Furthermore, re-explored flaps often have a poor appearance, making it challenging for surgeons to decide whether further aggressive treatments are necessary. Laser Doppler (LD) imaging can provide noninvasive, real-time, and quantifiable monitoring for flap perfusion. This study aimed to utilize fixed-timing LD to assist in postoperative free flap monitoring, especially in re-explored flaps. Material and Methods: We retrospectively analyzed free anterolateral thigh (ALT) flap transfers with at least 1 re-exploration surgery from 2018 to 2022. Fixed-timing LD scans were conducted once a day on weekdays, and the flux mean of the flap and its adjacent reference healthy skin was obtained via an LD imager. The perfusion index (PI) was calculated as the percentage difference of flux mean between the flap and the reference. Timing of compromise, surgical findings and flap outcomes were recorded. Re-explored cases were matched with non–re-explored cases by propensity score matching for age, sex, and recipient site. Receiver operating characteristic curves and Youden's index were used to identify a PI cutoff value to define flap compromise. Post re-exploration outcomes were categorized into flap survival, partial necrosis, and failure. Post reexploration LD data were analyzed with the Wilcoxon test. Results: Forty-seven re-explored free ALT flaps were included. Ten re-explored cases with LD scans before compromise on postoperative day 1 were matched with 20 nonreopened cases. A PI threshold value < −0.62 could identify flap compromise with 80% sensitivity and 70% specificity. In the flap survival group, the mean PI mean was −0.61 ± 0.03 in 32 cases within 24 hours after re-exploration, which was higher than the PI threshold. A significant difference in PI mean was found between the survival and partial necrosis groups (−0.61 ± 0.03 vs −0.86 ± 0.02, P = 0.034). Conclusions: When facing uncertain circulation after free flap transfers, LD imaging can provide reliable and objective method for postoperative monitoring. A PI value ≤ −0.62 could identify free ALT flap compromise. This PI threshold value could be applied to re-explored flaps, providing an option to evaluate those in which compromise is suspected.