Interference of Cerebral Near-Infrared Oximetry in Patients with Icterus

Near-infrared spectrophotometry assesses cerebral oxygen saturation (ScO2) based on the absorption spectra of oxygenated and deoxygenated hemoglobin and the translucency of biological tissue in the near-infrared band. In patients with icterus, however, bilirubin can potentially hinder cerebral oximetry. In 48 patients undergoing orthotopic liver transplantation, we related total plasma bilirubin to ScO2 as determined from spectrophotometry with wavelengths of 733 and 809 nm. Before surgery, ScO2 was 59% (15%–78%) (median with range) and bilirubin was 71 (6–619) μmol/L with a negative correlation (r = −0.72;P < 0.05). The 95% prediction interval included the lowest measurable ScO2 of 15% at a bilirubin level of 370 μmol/L. During reperfusion of the grafted liver, the ScO2 increased by 7% (−8% to 17%) (P < 0.05), and bilirubin did not influence this increase. In one patient, the ScO2 remained below 15% despite a decrease in bilirubin from 619 to 125 μmol/L, suggesting that tissue pigmentation deposits also absorb light. In conclusion, bilirubin dampens the spectrophotometry-determined cerebral oxygen saturation at 733 and 809 nm. A bilirubin level of 370 μmol/L, tissue pigment deposits, or both, may render determination of cerebral oxygen saturation impossible. Even at high bilirubin values, changes in cerebral perfusion may be visible. Implications In 48 patients undergoing liver transplantation, the interference of icterus on cerebral oximetry by near-infrared light was investigated. Bilirubin absorbed the near-infrared light and lowered the measured cerebral oxygen saturation. Even at high bilirubin values, changes in cerebral oxygenation, as seen during reperfusion of the grafted liver, may be visible.