BACKGROUND: High rates of ischemia related morbidity are seen in esophageal surgery where adequate monitoring of gut perfusion is needed, but a reliable method for measuring real-time tissue perfusion is not available. The aim of this study was to develop an optical fiber spectroscopy (OFS) system to provide an accurate assessment of the critical components of tissue viability in an animal model of esophageal surgery. METHODS: An opossum model was used with creation of an ischemic gastric conduit for esophageal replacement (n=14). The tissue blood content and oxygen saturation in the gastro-esophageal anastamosis was measured by optical spectroscopy (590-850 nm). Measurements at the anastamotic site were made prior to the procedure (Base), immediately after creation of the neoesophagus (Immediate), 10 minutes after anastomosis (Nadir), and at 10 days post operatively (10 Day). Two optical fibers separated by 4 mm contacted the tissue intraoperatively. White light transmission from the 1st fiber to the 2nd fiber versus wavelength was analyzed by diffusion theory for light transport, yielding values for blood content (volume fraction whole blood) and oxygen saturation (hemoglobin in mixed arteriovenous vasculature). The averages of five measurements at each time point were compared using the paired t-test. RESULTS: The OFS system demonstrated a 25% increase in blood content between baseline and 10 Day values (p=0.005). There was no difference between blood content at baseline (0.99% ± 0.24%) and either immediate (0.93% ± 0.44%) or nadir (0.88% ± 0.43%) time points (p=0.572 and p=0.369, respectively). Tissue oxygen saturation was significantly decreased at both immediate (67.9% decrease, p=0.001) and nadir (71.1% decrease, p=0.001) points when compared to baseline. There was not a statistically significant difference between baseline (50.8% ± 22.4%) and 10 days (32.3% ± 27.4%) with respect to tissue oxygen saturation (p=0.109).DISCUSSION: Utilizing a robust model for gastrointestinal ischemia, this study demonstrated that OFS can accurately and repeatedly analyze critical components of perfusion. The OFS system determined objective levels of tissue oxygenation that precede the complications related to ischemia. The ability to directly assess tissue oxygenation in real time using OFS will provide clinicians with data by which to guide post-operative care and may lead to significant reductions in post-operative morbidity and mortality in esophageal and gastrointestinal surgery.