Block of the sacral segments in lumbar epidural anaesthesia

Background.. Block of the first sacral segment is often delayed in lumbar epidural anaesthesia. The addition of either epinephrine or sodium bicarbonate to the local anaesthetic enhances the efficacy of epidural block. We assessed the block of lumbo-sacral segments in lumbar epidural anaesthesia adding epinephrine and/or bicarbonate to lidocaine. Methods. Twenty-seven patients undergoing lumbar epidural anaesthesia with lidocaine 2%, 17 ml at L4-5 or L5-S1 were randomly divided into three groups. Plain lidocaine, lidocaine with 1:200 000 epinephrine or lidocaine-epinephrine-bicarbonate was administrated via an epidural catheter. The pain threshold after repeated electrical stimulation was used to assess the sensory block at the L2, S1, and S3 segments. Motor block was evaluated using the Bromage scale. Results. Patient characteristics were comparable between the groups. The pH of lidocaine in the lidocaine-epinephrine-bicarbonate group was significantly higher than that in other groups. Pain thresholds at the SI and S3 segments in the lidocaine-epinephrine-bicarbonate group were significantly higher than those in the lidocaine-epinephrine group. However, differences in the pain threshold at the L2 segment between groups were insignificant. The time to onset of sensory block at the SI and S3 in the lidocaine-epinephrine-bicarbonate group was significantly shorter than that in the lidocaine group. Pain threshold by pinprick test was approximately within the 30-50 mA range. Conclusion. A combination of lidocaine, bicarbonate, and epinephrine increases the pain threshold over the sacral segments.