During the operation, once the gastric conduit has been mobilized and positioned, and once the anastomotic site has been identified by the surgeon, the assigned RSA will provide the Wipox instrument to the fellow (the primary surgeon will be blinded to the result) who will then obtain one measurement from the anastomotic site.

In addition to the one Wipox measurement at the planned anastomotic site, the RSA will collect the systemic pulse oximeter reading, blood pressure, and heart rate at the time of the Wipox measurement. These measurements will be obtained as both internal controls of the accuracy of the Wipox (matching the Wipox pulse rate with the patient's), as well as additional variables to control for when assessing factors which might contribute to oxygen saturation at the anastomotic site. Pre-operative demographic information will be collected. This will include age, sex, any co-morbidities (cardiac, diabetes, respiratory), and use of pre-operative chemotherapy or chemo-radiotherapy.

The primary objective of this observational study is to determine whether in patients undergoing Ivor Lewis esophagectomy, low levels of tissue oxygenation at the anastomotic site are associated with increased risk of anastomotic leak (AL).

(age, co-morbidities, smoking history) and clinical variables (pre-operative therapy, intra-operative blood pressure and systemic oxygen saturation) with tissue oxygenation at the anastomotic site. Spearman rank correlation (for continuous variables) and Wilcoxon rank sum test (for categorical variables) will be used to test these associations.