The Effect of Intravenous Lidocaine on Somatosensory Evoked Potentials During Scoliosis Surgery

Abstract

In Response: We read with interest Dr. Klasen's response to our study [1]. Dr. Klasen is correct in stating that there have been recent studies investigating the effects of lidocaine on somatosensory evoked potentials (SSEPs). The studies by Kasaba et al. [2] and Klasen et al. [3] reported no significant changes in the amplitude or latencies of the median or posterior tibial nerve SSEPs, respectively. Both reports used adult patients with an age range of 19-75 yr, and a mean age of 45.5 yr in Klasen et al.'s report. Schubert et al. [4] reported decreased amplitudes in the cortical SSEPs by approximately 25%-30% with minimum prolongation of the latencies. This study also involved adults from 22 to 46 yr of age. Our study involved neurologically normal children aged 12.5-15 yr of age. It has been shown that cortical responses in children are more sensitive to anesthetics [5]. In addition, Klasen et al.'s study did not involve the use of nitrous oxide, which was used in our study. Granted, the effects of nitrous oxide may be minimal, but when combined with intravenous lidocaine, there may have been some synergistic effect. This may have contributed to the changes we observed in the cortical responses. Schubert et al. [4] reported decreased amplitudes in the cortical SSEPs by approximately 25%-30% with minimum prolongation of the latencies. This study also involved adults from 22 to 46 yr of age. Regarding the hypothesis of seizure activity raised by Dr. Klasen, the assumption is that the epileptiform activity is random and not time-locked to the somatosensory stimulation, as the evoked response is. The seizure activity would be averaged out. Therefore, the epileptiform activity should not significantly change the SSEP response. In addition, there was no history of a seizure disorder in either patient. In summary, we feel that one cannot extrapolate findings from the adult population and apply them to children. Therefore, further studies in children are still recommended. Sandra L. Helmers, MD Department of Neurology; Children's Hospital; Harvard Medical School; Boston, MA 02115 Robert Brustowicz, MD Department of Anesthesiology; Children's Hospital; Harvard Medical School; Boston, MA 02115