Effects of ketamine on MAC_(BAR) of sevoflurane in patients undergoing abdominal surgery

Objective To evaluate the effects of ketamine on the minimum alveolar concentration of scvoflurane for blunting adrenergic responses to skin incision (MAC_(BAR)) in patients undergoing abdominal surgery. Methods Forty-four ASA Ⅰ or Ⅱ patients aged 30-60 yr undergoing elective abdominal surgery were randomly divided into 2 groups (n=22 each) : control group (group K_0) and ketamine group (group K_1). Anesthesia was induced with propofol 2 mg/kg and fentanyl 3 μg/kg. Tracheal intubation was facilitated with cisatracurium 0.15 mg/kg. The patients were mechanically ventilated. Anesthesia was maintained with sevoflurane inhalation (the initial end-tidal concentration 3% ). Ketamine at 14 μg·kg~(-1)·min~(-1) was infused at the same time in group K,. The patients' response to skin incision was described as positive if MAP or HR increased by≥15%. If the response was positive, the end-tidal concentration of sevoflurane for the next patient was increased by 0.5%, whileif negative, decreased by 0.5% . Results The MAC_(BAR) of scvoflurane was 3.25 % (95 % confidence interval 3.05%-3.45%) in group K_0, and 2.20% (95% confidence interval 1.96%-2.44%) in group K~1. The MAC_(BAR) of sevoflurane was significantly lower in group K~1 than in group K_0 (P<0.05). Conclusion Ketamine infusion at 14 μg·kg~(-1)·min~(-1) can reduce MAC_(BAR) of sevoflurane and enhance the inhibitory effect of sevoflurane on the stress response. Key words: Ketamine; Anesthetics; inhalation; Dose-response; relationship; drug