AbstractBackgroundPerfusion plays an important role in anastomotic healing. Indocyanine-green fluorescence angiogram allows objective bowel perfusion assessment. This study aimed to investigate the impact of perfusion assessment on intraoperative decision during left-sided colorectal resections. MethodThis was a prospective, single-centre, observational study recruiting patients with left-sided colorectal resections. Perfusion of bowel segment was assessed with ICG fluorescence angiogram prior to resection and anastomosis intra-operatively. The planned transection site and the actual transection site after perfusion assessment were compared. The decision for diversion stoma was also evaluated. Results110 patients with cancer of the sigmoid colon (29.1%) and rectum (70.9%) were recruited. Total mesorectal excision was performed in 51.8% of patients. The transection site was revised in 34.5% of cases: 30.9% more proximally and 3.6% more distally. The median distance between the intended and actual transection sites was 2 cm (range 1–17 cm). A proximal revision in the transection site was more likely seen in rectal cancers (p = 0.036, OR 3.58, 95% CI 1.09–11.78) and relatively under-perfused left colon (p = 0.036, OR 1.01, 95% CI 1.01–1.02). Three (2.7%) patients were spared from a diversion stoma. The overall anastomotic leakage rate was 5.5%. ConclusionICG fluorescence angiogram altered operative decisions in a significant proportion of cases. The impact on transection site was more pronounced in patients with rectal cancers and those with relatively under-perfused colon.