[Intravenous infusion of methylene blue to visualize the ureter in laparoscopic colorectal surgery]

Objective: Intraoperative localization of the ureter can contribute to accurate dissection and minimize ureteral injury in colorectal surgery. We aim to summarize a single center's experience of fluorescence ureteral visualization using methylene blue (MB) and explore its visualization efficiency. Methods: This is a descriptive case-series-study. Clinical data of patients who had undergone laparoscopic colorectal surgery and fluorescence visualization of the ureter in the Gastrointestinal Surgery Department of Guangdong Provincial People's Hospital from March 2022 to May 2022 were retrospectively collected. Patients with incomplete surgery videos, renal insufficiency, or allergic reactions were excluded. MB was infused with 0.9% NaCl at 1.0 mg/kg in 100 mL of normal saline for 5 to 15 minutes during laparoscopic exploration. Imaging was performed using a device developed in-house by OptoMedic (Guangdong, China) that operates at 660nm to achieve excitation of MB. Clinical information, MB dosage, rate of successful fluorescence, time to fluorescence, operation time, blood loss, intraoperative blood oxygen levels, pathological staging, changes in renal function, and post-operative complications were retrospectively analyzed. Results: The study cohort comprised 27 patients (24 men and 3 women) with an average age of (60.25±16.95) years and an average body mass index of (21.72±3.42) kg/m². The dosage of MB was 0.3-1.0 mg/kg and the infusion time was 5-15 minutes. Fluorescence signals were detected in all patients. The median time to signal detection was 20 (range, 10 to 40) minutes after MB infusion. The range of intraoperative blood oxygen fluctuation averaged 2.5% (range, 0 to 7.0%). The median change in creatine concentration was -1.3 (range, -17.2 to 29.2) µmol/L. No patients had complications associated with use of MB. Fluorescence visualization of the ureter was very valuable clinically in two patients (thick mesentery, stage T4). Conclusion: MB is a safe and effective means of visualizing the ureter by fluorescence during laparoscopic colorectal surgery, especially when the procedure is difficult. MB in a dosage of less than 1 mg/kg can slowly infused for more than 5 minutes during laparoscopic exploration. During the infusion, attention must be paid to blood oxygen fluctuations.