The relationship between bispectral index and propofol during target-controlled infusion anesthesia: A comparative study between children and young adults

BACKGROUND: In this prospective study, we compared the relationship between propofol concentrations and bispectral index (BIS) in children versus young adults anesthetized with target-controlled infusion (TCI) of propofol. METHODS: Forty-five prepubertal subjects (children) and 45 postpubertal subjects (adults) were studied. All patients were anesthetized with TO of propofol, based on the Kataria et al.'s model for children and on the Schnider et al. adults. All data from the BIS and the TCI system were continuously recorded using Rugloop software. Remifentanil was continuously administered throughout the study (0.25 mu g . kg(-1) . min(-1)). In all patients, after the end of surgery, a 12-min period with a stable target plasma concentration (Ct) of propofol, randomly assigned at 2, 3, 4, 5, and 6 mu g/mL, was performed. In addition, in most of the patients, another 12-min period was performed during which the BIS was targeted at 50 +/- 5. After each 12-min steady-state period, the Ct and BIS were noted and the plasma concentration of propofol was measured (Cm). The Ct and Cm corresponding to half maximal effect (BIS50) was determined by the Hill equation, and by targeting BIS at 50. RESULTS: In children, as in adults, BIS values were highly correlated with the corresponding Ct or Cm of propofol following classical E-max dose-response curves. The ECt(50) and the ECm50, derived from the dose-response curves, were higher in children than in adults: ECm50: 4.0 (3.6-4.5) mu g/mL vs 3.3 (3.0-3.7) mu g/mL [mean (95% CI)], P < 0.001; as well were the Ct and Cm clinically obtained when BIS was targeted at 50 (Cm-50: 4.3 +/- 1.1 mu g/mL vs 3.4 +/- 1.2 mu g/mL. (mean +/- SD) P < 0.05, children versus adults). Cm was generally under-estimated by the Ct, and the bias was higher in children than in adults: 2.6 +/- 2.6 mu g/mL, vs 1.7 +/- 1.6 mu g/mL, (P 0.05). CONCLUSIONS: The good relationship between propofol and BIS demonstrated in children as in adults suggested a slightly lower sensitivity to propofol in children. As the predictability of plasma propofol concentrations with the classical pharmacokinetic/pharmacodynamic models is limited in children, a cerebral pharmacodynamic feedback, such as BIS, may be useful in this population.