Objective To determine the median effective concentration (EC50) of epidural lidocaine inhibiting herpetic neuralgia.Methods The patients with thoracic or lumbar herpetic neuralgia,aged 20-60 yr,with body mass index of 18-25 kg/m2,of ASA physical status Ⅰ or Ⅱ,were included in the study.Epidural catheter was placed under the guidance of the digital subtraction angiography (DSA).An injection of iohexol mixed with lidocaine was given under the guidance of DSA to make sure that drug solution covered all the injured nerve roots.The initial concentration of lidocaine was 0.37％.The concentration was determined by up-and-down sequential allocation.Each time the concentration of lidocaine increased/decreased in the next patient depending on whether or not the analgesia was effective.The ratio between the two successive concentrations was 1.06.Effective analgesia was defined as VAS score ≤ 1 within 30 min after administration.The EC50 and 95 ％ confidence interval of lidocaine inhibiting herpetic neuralgia were calculated using Dixon formula.Results The EC50 of lidocaine inhibiting herpetic neuralgia was 0.199 ％ and the 95 ％ confidence interval was 0.168 ％-0.216 ％.Conclusion The EC50 of epidural lidocaine required to inhibit herpetic neuralgia is 0.199％.

Objective To compare the onset time, duration and adverse effects of stellate ganglion block (SGB) with different concentrations of lidocaine. Methods Two hundred and forty ASA Ⅰ or Ⅱ patients (97 male, 143 female) aged 37-76 yr weighing 48-79 kg were randomly divided into 3 groups ( n = 80 each): group A, B and C received unilateral SGB with 8 ml of 0.6%, 0.8% and 1.0% lidocaine respectively. Unilateral SGB was performed by the same anesthesiologist in all patients. Successful SGB was verified by Homer's syndrome. The onset time, duration and adverse effects were recorded. Results Homer's syndrome was observed in all patients. There was no significant difference in onset time among the 3 groups. The duration of action was significantly longer in group B and C than in group A and in group C than in group B. There was no significant difference in the adverse effects including recurrent laryngeal nerve block, brachial plexus block, local anesthetic intoxication and transient loss of consciousness among the 3 groups. Conclusion SGB can be induced with either 0.6%, 0.8% or 1.0% lidocaine with comparable effectiveness. We suggest using lower concentration of lidocaine.