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.