Abstract: Objective To investigate the effects of different depth of anesthesia on sublingual microcirculation. Meth⁃ ods ASA grade Ⅰ-Ⅱ patients (n=20) were scheduled for elective thyroid surgery and included in the prospective observa⁃ tional study. Midazolam 0.05 mg·kg, sufentanil 0.3 μg·kg-1 and rocuronium 0.6 mg·kg-1 were administrated intravenously to induce anesthesia which was then maintained by continuous intravenous infusion of propofol. Target medication concentra⁃ tion increased 0.5 mg·L-1, regulated based on BIS. The patients underwent endotracheal intubation and mechanical ventila⁃ tion. Sublingual microcirculations were evaluated by sidestream dark field (SDF) imaging at T1 (BIS baseline ), T2 (50 < BIS ≤ 60), T3 (40 0.05). Conclusion When BIS value sit between 40 and 50, it can best inhibit stress response and attenuate the agitation of microcirculation.

Key words: microcirculation, tongue, stress, depth of anesthesia, bispectral index (BIS), sidestream dark-field technique