Hepatic artery flow, inspired oxygen, and hemoglobin determine liver tissue saturation measured with visible diffuse reflectance spectroscopy (vis-DRS) in an in vivo swine model

Background Prompt diagnosis of vascular compromise following pediatric liver transplantation and restoration of oxygen delivery to the liver improves organ survival. vis-DRS allows for real-time measurement of liver tissue saturation. Methods The current study used vis-DRS to determine changes in liver saturation during clinically relevant conditions of reduced oxygen delivery. In an in vivo swine model (n = 15), we determined liver tissue saturation (StO2) during stepwise reduction in hepatic artery flow, different inspiratory oxygen fraction (FiO(2)), and increasing hemodilution. A custom vis-DRS probe was placed directly on the organ. Results Liver tissue saturation decreased significantly with a decrease in hepatic artery flow. A reduction in hepatic artery flow to 25% of baseline reduced the StO2 by 15.3 +/- 1.4% at FiO(2) 0.3 (mean +/- SE, p < .0013), and by 8.3 +/- 1.9% at FiO(2) 1.0 (p = .0013). After hemodilution to 7-8 g/dl, StO2 was reduced by 31.8% +/- 2.7%, p < .001 (FiO(2) 0.3) and 26.6 +/- 2.7%, p < .001 (FiO(2): 1.0) respectively. Portal venous saturation during low hepatic artery flow was consistently higher at FiO2 1.0. The gradient between portal venous saturation and liver tissue saturation was consistently greater at lower hemoglobin levels (7.0 +/- 1.6% per g/dl hemoglobin, p < .001). Conclusions Vis-DRS showed prompt changes in liver tissue saturation with decreases in hepatic artery blood flow. At hepatic artery flows below 50% of baseline, liver saturation depended on FiO2 and hemoglobin concentration suggesting that during hepatic artery occlusion, packed red blood cell transfusion and increased FiO(2) may be useful measures to reduce hypoxic damage until surgical revascularization.