RESUMEN
To determine the best concentration of lidocaine for caudal anesthesia under supplementary general inhalation anesthesia via faee mask, 85 children aged 1 month to 12 years scheduled for inpatients or outpatients inguinal herniorraphy were randomiaed to receive caudal anesthesia with lidocaine in one of four concentrations(0.5, 0.75, 1.0 or 1.5%) mixing l: 200,000 epinephrine. After incision, gradual reduction in inspired halothane resulted, if tolerated by subject, in an inspired concentration of 0.5% at 10 minutes after incision. Percents of patients who received more than 0.5% of endtidal halothane concentration at hernia sac ligation were 30.0, 28.6, 16.7 and 20.0% in the subjeets receiving 0.5, 0.75, 1.0 and 1.5% lidocaine, respectively. There was no significant differences among groups in pain/discomfort scores and caudal effectiveness scores. A subject receiving 1.5 % lidocaine complained of leg weakness and another of retching. About ninety percents of all subjects could gain the analgesic levels at T dermatome although most of subjects receiving 0.5% lidocaine had the short duration less than 1 hour. Postoperative analgesic effects in the subjects receiving 1.0% lidocaine were superior to those receiving 0.5 and 0.75% solution. Although all concentrations were effective for combined general-caudal anesthesia in children, we conclude that 1.0% lidocaine offers the best combination of effectiveness, postoperative analgesia, adequate anesthetic levels and less complication for pediatric inguinal herniorraphy.