Laboratory variables associated with low near-infrared cerebral oxygen saturation in icteric patients before liver transplantation surgery.

BACKGROUND: Although regional cerebral oxygen saturation (rSO₂) measurements can detect disturbances in cerebral oxygenation, their usefulness is limited in patients with hyperbilirubinemia. We examined the relationship between rSO₂ and other laboratory variables that may affect interpretation of low rSO₂ in awake patients with end-stage liver disease before liver transplantation surgery.
METHODS: Before induction of general anesthesia, rSO₂ was measured in 164 patients with liver cirrhosis (Child class A/B/C = 19/41/104) and 8 with fulminant hepatic failure. Patients with West Haven hepatic encephalopathy of grade 3 or 4 were excluded. Relationships between rSO₂ and laboratory variables were evaluated by correlation and multivariate regression, and by receiver operating characteristic curve analysis.
RESULTS: Univariate analyses showed that rSO₂ (median 58.5%, range 15% to 82%) correlated with serum total bilirubin, hemoglobin (Hb), creatinine, sodium, and magnesium concentrations, and prothrombin time (P < 0.001 each), but not with serum concentrations of glucose, albumin, potassium, and ammonia. Multiple logistic regression analysis showed that only elevated total bilirubin (range 0.4 to 66 mg/dL; odds ratio [OR] = 1.31; 95% confidence interval [CI] = 1.18 to 1.45) and low Hb (range 5.3 to 15.7 g/dL; OR = 0.21; 95% CI = 0.11 to 0.43) were independently related to rSO₂ <50%. The optimum cutoff points for observing an rSO₂ < 50% were total bilirubin >7.2 mg/dL (sensitivity 89%, specificity 90%) and Hb <9.6 g/dL (sensitivity 70%, specificity 82%).
CONCLUSIONS: High total bilirubin and low Hb concentrations were independently associated with rSO₂ values below 50% in end-stage liver disease patients awaiting liver transplantation. The results of this study identify patients in whom a low rSO₂ may be an artifact rather than cerebral ischemia.