Randomised Controlled Trial of Fluorescent Urography Using Intravenous Methylene Blue Compared to White Light Alone in Left-sided Colorectal Surgery

This randomised controlled trial will test whether intravenous methylene blue, viewed with a special fluorescence camera, helps surgeons identify the left ureter (the tube that carries urine from the kidney to the bladder) more quickly during left-sided colorectal (bowel) surgery. Ureter injury is a rare but serious complication, and in some patients the ureter is hard to see under standard white light. Adults having open, laparoscopic, or robotic left-sided colorectal surgery at Prince of Wales Hospital (Hong Kong) will be screened; if the left ureter cannot be clearly seen before dissection, they will be randomly assigned to either fluorescence imaging with methylene blue or standard white-light vision alone.

The main outcome is the time from starting dissection to first seeing the left ureter. The study will also record how often the ureter is seen at set time points, operating times, surgeon-rated ease and confidence, any changes to the surgical plan, complications, and ureteric injuries. The goal is to find out whether the fluorescence method can make ureter identification faster and easier, potentially improving safety without needing invasive preoperative ureteric stents.

Inclusion criteria

• Aged ≥18 years
• Scheduled to undergo open, laparoscopic or robotic left-sided colorectal surgery, including left colectomy, high anterior resection, low anterior resection, abdominoperineal resection, subtotal colectomy and total colectomy.

Exclusion criteria

• Unable to understand the aims and objectives of this study and unable to give consent for participation
• Known allergy to methylene blue
• Pregnant
• Taking selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, monoamine oxidase inhibitors, or tricyclic antidepressants (risk of serotonin syndrome)
• Significant renal or hepatic impairment
• Presence of renal or ureteric obstruction
• History of G6PD deficiency (risk of hemolytic anemia)