Use of the Liver Tissue Oxygenation Index as a Noninvasive Parameter of Intestinal Ischemia in Rabbits

Objective The tissue oxygenation index (TOI), measured by spatially resolved spectroscopy (SRS), reflects the ratio between oxygenated and deoxygenated tissue hemoglobin. We investigated whether liver TOI is a noninvasive parameter for early detection of intestinal ischemia. Methods In seven adult New Zealand rabbits the superior mesenteric artery (SMA) and vein were exposed by laparotomy. The SRS probe was attached at the skin above the liver to calculate the TOI. The bowel (SbO2) and peripheral (SpO2) oxygen saturation were continuously measured. The SMA was occluded, creating small bowel ischemia for 90 minutes. Then reperfusion was started for 1 hour. The median TOI and interquartile range (IQR) of the TOI were calculated. A paired Wilcoxon test was used to evaluate changes in the liver TOI and SpO2 during ischemia and reperfusion. Results The median TOI was 54.3% (IQR 8) at the start of ischemia, 54.9% (IQR 9) after 30 minutes, 51% (IQR 11) after 60 minutes, and 50.3% (IQR 10) after 90 minutes. The median TOI values were 46.3% (IQR 5) after 30 minutes of reperfusion and 41.2% (IQR 5) after 60 minutes. The decrease in TOI became significant (p < 0.05) after 90 minutes of ischemia. The SpO2 was stable during the experiment. Discussion A significant decrease in liver TOI was seen after 90 minutes of occlusion of the SMA and is likely to be the consequence of bowel ischemia. The further decrease after reperfusion might reflect reperfusion injury. Liver TOI may be a new tool for noninvasive early detection of intestinal ischemia and reperfusion. Further study is needed to confirm these findings.