Impact of ageing on sevoflurane's hypnotic potency and induction kinetics during wash-in period: A prospective observational study.

Background and aims: The age-dependent decline in sevoflurane's minimum alveolar concentration is well established. However, the relationship between ageing and its hypnotic potency at the effect-site concentration (Ceff) remains unclear. This study aimed to evaluate the impact of ageing on sevoflurane's hypnotic potency and induction kinetics during the wash-in period.

Methods: This prospective observational study enroled 83 female patients stratified by age into four decades: 30-39, 40-49, 50-59, and 60-69 years. Anaesthesia was induced using 5% sevoflurane in a non-rebreathing manner. We continuously recorded bispectral index (BIS) values and end-tidal sevoflurane concentrations during the 4 min wash-in period, with Ceff values calculated through pharmacokinetic modelling. Subsequently, the end-tidal concentration was maintained at 1.5% for 20 min (10 min equilibration + 10 min stabilisation) at 2 L/min to achieve a cerebral steady-state, and the final stabilised BIS value was calculated. One-way ANOVA with Bonferroni post-hoc correction or Kruskal-Wallis test was used to compare continuous variables. Pearson's Chi-square test was used to compare categorical variables, with the significant difference set at P < 0.05.

Results: During the wash-in period, the 60-69-year group exhibited a prolonged time from awakening to BIS 50 compared to younger cohorts (P < 0.05 or < 0.01). Ceff values exhibited progressively delayed kinetics with increasing age, but Ceff values of sevoflurane at BIS 50 were not different across the four age groups (P > 0.05). At a steady state of 1.5% sevoflurane anaesthesia, the intergroup analysis revealed no significant variations in BIS values.

Conclusion: The hypnotic potency of sevoflurane is preserved among female patients aged 30-69 years despite delayed induction kinetics in older individuals.