Anastomosis refers to the surgical connection between two segments of the bowel, typically performed during colon and rectal surgeries to restore the continuity of the digestive tract after a section has been removed. It is necessary that the ends of the tissue at the anastomotic site are healthy (and capable of healing properly) as this will prevent dreaded complications like anastomotic leaks or strictures which can occur in almost a fifth of patients leading to increased hospital length of stay, costs, and mortality.

Currently, the most widely used method for assessing tissue viability during anastomosis is indocyanine green fluorescence angiography (ICG-FA). This technique involves injecting a fluorescent dye (indocyanine green) into the bloodstream, which highlights blood flow and tissue perfusion under a special camera. However, ICG-FA has limitations due to allergies and reliability due to the dye's rapid disappearance from the bloodstream. Additionally, the dye cannot be administered repeatedly. This study explores a new method of measuring tissue oxygenation by evaluating mucosal oxygen saturation (StO2) as an alternative to ICG-FA. By evaluating StO2 levels, the research aims to provide a more reliable and repeatable way to assess tissue viability without the drawbacks of using fluorescent dyes. Secondly, any blood supply interruption to the bowel will first lead to mucosal ischemia, which can potentially be reliably captured by measuring mucosal StO2 levels only.

In this single-center prospective single-arm study, we will evaluate whether mucosal StO2 levels are associated with or can predict anastomotic complications. This study will not involve any intervention that would affect the standard of care.

Virtually all patients undergoing elective colon and rectal resections undergo bowel anastomosis. These surgeries are often technically challenging, with significant morbidity and mortality in the case of an anastomotic leak, which can affect up to 21% of patients. In addition to increased morbidity and mortality, anastomotic leaks are associated with increased hospital length of stay and cost. Anastomotic leak following colon and rectal surgery is multifactorial, involving an intimate interplay of patient-related, tumor, and surgical risk factors. While decreased perfusion to anastomosis plays a central role in its pathophysiology. Poor perfusion at the anastomotic site can also lead to anastomotic strictures - requiring further reoperations , and in some cases, be equally catastrophic as anastomotic leaks.

As such, multiple attempts have been made to reduce the incidence of leaks. It is believed that the ability to accurately determine intraoperative tissue perfusion and oxygenation can help reduce the incidence of anastomotic leaks. Investigators have explored multiple modalities and benchmarks in human and animal models over the past three decades; these include colonic coloration, mesenteric pulsations, tissue perfusion using Doppler ultrasound quantitative visual analysis of tissue oxygenation using either indocyanine green or non-contrast tissue oxygenation imaging tools to detect predictors of anastomotic leak and hyperbaric oxygenation in mice models to improve anastomotic healing. While a few studies have found an association between low tissue oxygen tension and anastomotic leak development, there have only been a handful of large-scale human studies.

Currently, indocyanine green fluorescence angiography (ICG-FA) is the most widely accepted in this regard. It has shown a significant reduction in anastomotic leaks owing to a change in the resection margin. However, ICG-FA is contraindicated in patients with a history of contrast allergy. It also has a higher plasma disappearance, leading to an unstable fluorescence signal for the estimation of tissue congestion, causing reduced precision in estimates and an introduction of subjectivity and reduced standardization; furthermore, it cannot be repeated intraoperatively because of the increased risk of false positives. The newer imaging modalities focus on tissue oxygen tension (StO2) by mapping oxygen saturation indices. They utilize multispectral illumination to accurately quantify StO2 levels by distinguishing between oxyhemoglobin and deoxyhemoglobin without the need for fluorescent dyes or repeat intraoperative evaluations, thereby improving efficiency and accuracy.

Studies that have used StO2 to predict anastomotic leak after colo-rectal surgery in humans have utilized serosal oxygen tension, and these have established safety, usability, and reliability, along with exploration of the link with anastomotic leak. However, since the mucosa exhibits the first signs of hypoxia, it might be a better target for predicting postoperative anastomotic complications. Such a theory has been explored using the Food and Drug Administration (FDA) 510k approved device (FUJIFILM Eluxeo Vision system; K203717) among patients undergoing thoracic esophagectomy, in which the results followed the aforementioned hypothesis. However, there is no literature on such an imaging modality used for colon and/or rectal resections and anastomosis.

In this prospective observational study we aim to investigate the association between mucosal StO2 levels and the incidence of anastomotic complications, including stricture and leak in colo-rectal surgery. We hypothesize that lower StO2 will be associated with higher anastomotic complications (stricture and leak [grades A, B, or C], as determined by the surgeon).

Inclusion Criteria:

• Adult patients (≥18 years).
• Undergoing a colo-rectal anastomosis.
• Patients who consent to study participation

Exclusion Criteria:

• Patients undergoing a revision surgery.
• Participants with missing data.
• Patients who do not undergo intraoperative ICG-FA and StO2 endoscopic imaging promptly after the formation of a viable anastomosis.

Patients meeting the eligibility criteria will be enrolled from the institution's colorectal surgery clinic in Nashville, TN

We will not share individual participant data (IPD) outside the study team due to privacy protections, consent limitations, and the risk of re-identification. Data will be stored securely and accessed only by authorized personnel. All results will be presented in aggregate form (summaries/tables) so that no individual can be identified.