Quantitative evaluation of anastomotic perfusion during colorectal surgery via indocyanine green fluorescence angiography: a narrative review

BACKGROUND AND OBJECTIVE: Quantitative studies of indocyanine green (ICG) are needed to optimize its evaluative potential in anastomotic perfusion during colorectal surgery. However, some limitations still existed in current studies about qualitative evaluations such as small-scale studies, the inconsistent concentration of the drug, the method of injection, etc. Therefore, this review summarized the primary quantitative parameters, image, method, and so on, during ICG fluorescence angiography aiming to further provide a theoretical basis for the application of ICG in laparoscopic colorectal surgery. METHODS: The following keywords “indocyanine green or ICG”, “anastomotic perfusion”, and “colorectal surgery” were applied to search for literature published from 2002 to 2022 in the PubMed, Web of Science, and Medline databases. Then, the information about ICG fluorescence angiography in quantitative evaluation of anastomotic perfusion during colorectal surgery was summarized. Through integrating the experiences derived from the literature and our research center, the crucial quantitative parameters [such as T0, Tmax, Fmax, and S (Fmax/Tmax)], image characteristics, and standard operational process for ICG fluorescence angiography were summarized. KEY CONTENT AND FINDINGS: Firstly, quantitative parameters, including T0, Tmax, Fmax, and S (Fmax/Tmax) during the ICG fluorescence angiography could predict anastomotic leakage, and thus should be recorded. Secondly, the image curve generated by the software might differ among patients, which included a filling period, reducing period, and platform period; some patients even presented a second fluorescence intensity peak. Finally, present studies presented great heterogeneity regarding the injection dose of ICG, observation distance from the laparoscope to the anastomotic site, software, and so on, during ICG fluorescence angiography in quantitatively evaluating the intestinal blood perfusion. CONCLUSIONS: This review points out the challenges of ICG fluorescence angiography in quantitative evaluation of anastomotic perfusion and gives some advice. However, some difficulties and issues are non-neglectable during the clinical implications of the quantitative evaluation of ICG, such as standardizing the specific cut-off value about the quantitative parameters, injection dose of ICG, observation distance from the laparoscope to the anastomotic site, software, and so on, during ICG fluorescence angiography in quantitatively evaluating the intestinal blood perfusion to eliminate heterogeneity.