Abstract
BACKGROUND: Visible light spectroscopy (VLS) is a technique used to measure the mucosal oxygen saturation during upper gastrointestinal endoscopy to evaluate mucosal ischemia, however in vivo validation is lacking. We aimed to compare VLS measurements with a validated quantitative microvascular oxygen tension (μPO(2)) measurement technique. METHODS: Simultaneous VLS measurements and μPO(2) measurements were performed on the small intestine of five pigs. First, simultaneous measurements were performed at different FiO(2) values (18%-100%). Thereafter, the influence of bile was assessed by comparing VLS measurements in the presence of bile and without bile. Finally, simultaneous VLS and μPO(2) measurements were performed from the moment a lethal dose potassium chloride intravenously was injected. RESULTS: In contrast to μPO(2) values that increased with increasing FiO(2), VLS values decreased. Both measurements correlated poorly with R(2) = 0.39, intercept 18.5, slope 0.41 and a bias of - 16%. Furthermore, the presence of bile influenced VLS values significantly (median (IQR)) before bile application 57.5% (54.8-59.0%) versus median with bile mixture of the stomach 73.5% (66.8-85.8), p = < 2.2 * 10(-16); median with bile mixture of small bowel 47.6% (41.8-50.8) versus median after bile removal 57.0% (54.7-58.6%), p = < 2.2 * 10(-16)). Finally, the VLS mucosal oxygen saturation values did not decrease towards a value of 0 in the first 25 min of asystole in contrast to the μPO(2) values. CONCLUSIONS: These results suggest that VLS measures the mixed venous oxygen saturation rather than mucosal capillary hemoglobin oxygen saturation. Further research is needed to establish if the mixed venous compartment is optimal to assess gastrointestinal ischemia.