Flap warming improves intraoperative indocyanine green angiography (ICGA) assessment of perfusion. An experimental study

Abstract

Indocyanine green angiography (ICGA) is slowly replacing conventional methods of evaluating perfusion during flap surgery. Microcirculatory changes during flap elevation create a marked state of hypoperfusion intraoperatively leading to ICGA underestimation of tissue viability and consequent resection of viable tissue. We propose a novel method of flap warming to induce maximum vasodilation before performing ICGA to increase accuracy in assessing perfusion. Submental flaps harvested on a single perforator were created in 8 pigs. ICG angiography was performed in the intraoperative phase (ICGA-C), after inducing maximum vasodilatation by warming the flap at 42 °C (ICGA-W) and at 24H postoperative (ICGA-24). By setting a fluorescence threshold of 33% as indicative of necrosis, the flap surface deemed viable by ICGA was measured for ICGAC, ICGAW and ICGA24. The results were then compared to the actual flap survival observed clinically at 7 days. The mean of ICG-C predicted flap survival (FS-C = 49.17%) is 12.97% lower than the mean of actual flap survival on postoperative day 7 (FS=62.14%). The mean difference between ICG-W and ICG-24 predicted flap survival (FS-W and FS-24) and actual flap survival in the postoperative day 7 (FS) is lower, 3.13% and 2.15%, respectively. Average perfusion recovery over 24 h was 10.83% (FS-24-FS-C). Conventional intraoperative ICGA underestimated perfusion in all cases. Warming the flap intraoperatively and achieving maximum vasodilation mitigates the effects of vasoconstriction and mimics the microcirculatory environment encountered at 24 h. Performing angiography after induced vasodilation improves ICGA assessment of flap perfusion.