Abstract

The effect of lumbar epidural analgesia with similar volumes (about 25 ml) of 0.25% and 0.5% bupivacaine on early (< 0.5 seconds) somatosensory evoked potentials (SEPs) to electrical stimulation of the S1, L1, and T10 dermatomes was examined in two groups of ten patients. Level of sensory analgesia to pinprick was T5.7 ± 0.8 and T6.4 ± 0.7 in the 0.25% and 0.5% bupivacaine group, respectively. Motor blockade was more pronounced in the 0.5% bupivacaine group ( p < 0.05). Despite similar analgesia to pinprick, SEPs were more reduced during 0.5% bupivacaine than during 0.25%. These results support previous findings that quantitative assessment of neural blockade by SEP measurements may be more precise than pinprick analgesia.