In this prospective, non-randomized cohort study, real-time intraoperative visualization using near-infrared-fluorescence by indocyanine green injection (ICG-NIRF) is performed at two to three time points during procedures of upper GI, lower GI and hepatobiliary surgery with anastomosis formation in open or laparoscopic surgery. Postoperatively, a detailed software-based assessment of each recording is performed to determine the objective ICG-NIRF perfusion rate before and after anastomosis formation, which is then correlated with the 30 day postoperative clinical outcome including occurrence of anastomotic leak.

Near-infrared-fluorescence by indocyanine green (ICG-NIRF) utilises the fluorescent property of intravenously injected indocyanine green (ICG) as an intravascular indicator of tissue and bowel perfusion.

The investigators hypothesise that ICG-NIRF is a suitable, reliable and precise method of visualisation of the blood supply and bowel perfusion in the area of gastrointestinal and hepatobiliary anastomosis formation.

In this prospective, non-randomized cohort study, the respective upper GI, lower GI or hepatobiliary procedure with anastomosis is performed according to standard of care and indication for the corresponding disease including non-malignant, malignant and inflammatory conditions. The following procedures are included in the study, in open or laparoscopic surgery, according to the surgeon's choice:

Upper GI surgery:

• Esophageal resection
• Subtotal or total gastrectomy with or without jejunal pouch reconstruction
• Y-Roux-reconstruction
• Right or left colonic interposition (iso- or antiperistaltic)

Lower GI surgery:

• Jejunal or ileal segmental resection
• Ileal / Ileocoecal resection
• Colectomy with restorative ileal pouch formation and ileal-pouch-anal anastomosis
• Left or right-sided hemicolectomy
• Sigmoid resection
• Rectal resections (lower anterior resection (LAR), proctectomy with colo-anal anastomosis, abdominoperineal resection)
• Stoma closure

Hepatobiliary surgery:

- Pancreaticoduodenectomy

Written informed consent for participation and ICG-administration is obtained one day before surgery.

Intraoperatively, Indocyanine Green (ICG, VerDye, Diagnostic Green GmbH, Aschheim Germany, 25 mg vials) is dissolved in 5 mL sterile water to yield a 5 mg/mL concentration. It will then be administered intravenously at three consecutive time points as a bolus of 2 ml per time point at the most. The overall dose of ICG will amount to no more than 30mg of ICG per patient.

Real-time intraoperative visualization is performed with the SpectrumTM Fluorescence Imaging Platform (Quest Innovations, Middenmeer, The Netherlands) directly after each ICG injection assessing bowel perfusion at two different time points per anastomosis respectively: before and after anastomosis formation.

Postoperative NIRF-perfusion rate assessment Using the Quest Research SoftwareTM, the recordings before and after anastomosis formation will be analysed for their perfusion rate. This analysis will provide objective, quantitative data on the perfusion for a certain time frame which is determined by the length of the video recording. This data will be collected for statistical analysis and correlation with anastomotic leak as well as postoperative outcome.

Clinical data and follow-up Clinical data will be collected from all patients regarding anastomotic leak, bowel ischemia and necrosis as well as 30 day postoperative morbidity, mortality and length and cost of hospital stay.

Further data analysis will be performed using Microsoft Excel® and IBM SPSS®.

Inclusion Criteria:

• Age ≥ 18
• capability of signing informed consent
• diagnosis of malignancies of the upper gastrointestinal tract (GI), or malignancies of the lower GI, or malignancies of the hepatobiliary system, refractory ulcerative colitis, or Crohn's disease, or acute, inflammatory, degenerative functional or anatomical disorders
• Surgery possible and medically indicated to the diagnosis (esophageal resection, or subtotal or total gastrectomy, or Y-Roux reconstruction, or right or left colonic interposition, or small bowel segment resection, or ileocecal resection, or colectomy, or proctectomy with restorative ileoanal pouch (one or two-stage), or left or right hemicolectomy, or sigmoid resection, or rectal resection (deep anterior resection (TAR)), or proctectomy with colo-anal anastomosis, or abdominoperineal resection, or stoma closure, or pancreaticoduodenectomy

Exclusion Criteria:

• liver disfunction (MELD score > 10)
• ICG (indocyanine green) specific exclusion criteria as per literature (intolerance to indocyanine green or sodium iodide, iodine allergy, hyperthyroidism, autonomous thyroid adenoma, focal or diffuse autonomies of the thyroid, previously badly tolerated injection of ICG)
• pregnancy or breastfeeding