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Increasing the Accuracy of NIR Fluorescence Angiography in Assessing Flap Viability Using an Intraoperative Thermal Challenge
Maximilian V. Muntean, MD, PhD; Filip Ardelean, MD, PhD; Ileana R. Matei, MD, PhD; Alexandru V. Georgescu, MD, PhD
Plastic Surgery and Reconstructive Microsurgery Clinic, UMF Iuliu Hatieganu, Cluj Napoca, Romania

Introduction: Indocyanine green (ICG) angiography is a reliable method of predicting flap survival. It provides the surgeon real time information regarding flap vascularization and it can be used intra-operatively to guide resection of nonviable tissue prior to flap inset. However, the blood flow pattern in a flap immediately after harvest is reduced. Skin perfusion recovers gradually reaching a maximum point after 24h, thus intraoperative use of ICG angiography underestimates flap viability. We used a local skin warming procedure to induce vasodilatation and increase intra-operative flap perfusion comparing the results to those observed clinically at 72h.

Materials and Methods: Submental flaps were created in 8 pigs. The flaps were harvested on a single submandibular perforator. ICG angiography using the Artemis System (Quest Medical Imaging) was performed three times: After raising the flap (ICG-Cold), after flap warming at 42C (ICG-Warm), and at 24h (ICG-24h). All perfusion values were analyzed using the ImageJ processing software with a fluorescence threshold of 33%. A perfusion map was created for each flap, and the ICG perfusion values were used to calculate the viable flap area and the predicted necrosis for each flap. The values obtained were then compared to the actual necrosis observed clinically at 72h. Image Analysis: The values recorded during the ICGA were analyzed separately. Three angiography's were performed for each flap. ICG-Cold, ICG-Warm and ICG-24h. We calculated the surface area of the predicted necrosis in each case. We then compared the actual necrotic surface area observed clinically at 72h with the results obtained during the angiography.

Results: Flap perfusion increased significantly in the first 24H, with an average of 10,82%. ICGA-Cold underestimated flap perfusion in all cases by an average of 14,17%. After flap warming and induced vasodilatation ICGA-Warm underestimated perfusion with an average of 4,33%. The difference in perfusion between ICGA-Warm and ICGA-24h is just under 1% (0,98%). The theorerical tissue loss after flap warming was reduced from 14,17% to just 4,33% (9,84%)

Conclusion: ICGA performed performed after flap harvesting underestimates perfusion in all cases. Intra-operative ICG angiography performed after inducing vasodilatation by local skin warming at 42OC provides perfusion values similar to those obtained at 24h and correlates with flap survival at 72h. Local warming increases the accuracy of ICG angiography in predicting flap survival while reducing the amount of viable tissue sacrificed.

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