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 a nd the translucency of biological tissue in the near-infrared band. In pati ents with icterus, however, bilirubin can potentially hinder cerebral oxime try. In 48 patients undergoing orthotopic liver transplantation, we related total plasma bilirubin to SCO2 as determined from spectrophotometry with w avelengths of 733 and 809 nm. Before surgery, SCO2 was 59% (15%-78%) (media n with range) and bilirubin was 71 (6-619) mu mol/L with a negative correla tion (r = -0.72; P < 0.05). The 95% prediction interval included the lowest measurable SCO2 of 15% at a bilirubin level of 370 mu mol/L. During reperf usion 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 r emained below 15% despite a decrease in bilirubin from 619 to 125 mu mol/L, suggesting that tissue pigmentation deposits also absorb light. In conclus ion, bilirubin dampens the spectrophotometry-determined cerebral oxygen sat uration at 733 and 809 nm. A bilirubin level of 370 mu mol/L, tissue pigmen t deposits, or both, may render determination of cerebral oxygen saturation impossible. Even at high bilirubin values, changes in cerebral perfusion m ay be visible. Implications: In 48 patients undergoing liver transplantatio n, the interference of icterus on cerebral oximetry by near-infrared light was investigated. Bilirubin absorbed the near-infrared light and lowered th e measured cerebral oxygen saturation. Even at high bilirubin values, chang es in cerebral oxygenation, as seen during reperfusion of the grafted liver , may be visible.