Effects of low-dose ketamine on minimum alveolar concentration of sevoflurane in patients undegoing gynecological abdominal surgery

Objective To investigate the effects of the low-dose ketamine on the minimum alveolar concentration (MAC) of sevoflurane in patients undergoing gynecological abdominal surgery.Methods Fifty-one ASA Ⅰ or Ⅱ patients aged 36-49 yr with body mass index ≤ 30 kg/m2 scheduled for gynecological abdominal surgery were randomly divided into control group (group C, n = 29) and ketamine group (group K, n = 22) . The paitents were unpremedicated. In group K, a loading dose of ketamine 0.2 mg/kg was injected intravenously followed by infusion at a rate of 14 μg·kg-1 ·min-1 , while equal volume of normal saline was given in group C. Anesthesia was induced with inhalation of sevoflurane (end-tidal concentration 4%-5%, maintaining for 5 min) in both groups. Endotracheal intubation was performed. The patients breathed sevoflurane until the predetermined target end-tidal sevoflurane concentration was reached for at least 15 min before skin incision. Occurrence of body movement was determined by any visible contraction of the muscle bundle of trunk, limbs, head and neck during skin incision and/or within 60 s after skin incision. The initial end-tidal concentration of sevoflurane was set at 1.8 % .If body movement occurred, the end-tidal concentration of sevoflurane was increased by 0.2% , while if not, decreased by 0.2% . MACs of sevoflurane were calculated. Results The MAC of sevoflurane was 1.51% (95% confidence interval 1.45%-1.58%) in group K, and 2.49% (95% confidence interval 2.40%-2.57%) in group C, and there was significant difference between the two groups ( P < 0.05) . Conclusion Intravenous infusion of the low-dose ketamine can enhance the anesthetic effect of sevoflurane in patients undergoing gynecological abdominal surgery. Key words: Ketamine; Dose-response relationship,drug; Sevoflurane