Abstract: Objective To investigate the optimal anesthesia depth with closed-loop administration of propofol guided by bispectral index(BIS)monitor to effectively inhibit surgical stress response in patients undergoing robot-assisted radical thyroidectomy(RAT)via bilateral axillo-breast approach(BABA). Methods A total of 60 patients undergoing BABA-RAT were enrolled and randomly assigned to the high target BIS group(55±5, n=30)and low target BIS group(45±5, n=30). Heart rate(HR), mean arterial pressure(MAP)were measured at the time points of pre-induction of anesthesia(T₀), 1h after operation beginning(T₁), the end of operation(T₂)and 6 h after operation(T₃). Serum concentration of IL-6 and C-reaction protein(CRP)were measured at T₀, T₂, T₃ and T₄(24 h after operation). Propofol consumption and incidence of adverse events were recorded. Results Propofol consumption was higher in the low target BIS group than in high target BIS group. There were no significant differences in MAP and HR at all the time-points between the two groups(P>0.05). Ascensional range of IL-6 and CRP were significantly lower in low target BIS group at T₃ and T₄(P<0.05). VAS was lower in low target BIS group 24 h postoperatively(P<0.05). No adverse events such as hypotension, intraoperative awareness or postoperative cognitive dysfunction occurred. Conclusion Anesthesia depth maintained at BIS of 45±5 is more effective than 55±5 to restrain surgical stress response and postoperative pain.

Key words: Bilateral axillo-breast approach, Robot surgical system, Thyroidectomy, Anesthesia depth, Closed-loop target control infusion, Surgical stress response