Fluorescence Intensity between Standard versus Diluted Indocyanine Green to Evaluate Flap Perfusion in Rats

The ideal dose for indocyanine green (ICG) has not been established yet, although 5 mg per mL is widely accepted for free flap evaluation. Due to its high price and rarity in developing countries, this preliminary study aimed to find the lowest concentration of ICG without reducing the fluorescence quality read by near-infrared camera in animal models. An experimental study was conducted on 25 Wistar rats divided into five groups based on the injected ICG, which was in 5 mg per mL, 3.75 mg per mL, 2.5 mg per mL, 1.25 mg per mL, and 0.5 mg per mL concentrations. The epigastric flap was elevated and confirmed to be vital on the fifth day. Upon confirmation, bolus IV injection of ICG was given via the tail, and the flap was read using near-infrared camera. The 25 different videos are randomized and rated individually in a blind manner by five microsurgeons, chosen beforehand. The videos are evaluated with a scoring system ranging from 0 to 4, assessing fluorescence visibility and flap vasculature. Nonetheless, the intraclass correlation coefficient is 0.779. There was no difference between standard and diluted ICG concentrations to evaluate flap perfusion. The 2.5 mg per mL concentration of ICG was the most favorable. This finding is not clinically relevant for application in human subjects yet. However, this study shows promising results for further usage of ICG in daily practice at a lower cost.