Ropivacaine produces sensory blockade in the lumbar sacral region more frequently than mepivacaine in lower thoracic epidural anesthesia.

PURPOSE: The first sacral nerve has the largest diameter among the spinal nerves and is resistant to local anesthetics. Ropivacaine is a newly developed local anesthetic. There is a possibility that a difference in chemical properties between ropivacaine and other local anesthetics produces a difference in the blockade of the S1 dermatome by lower thoracic epidural anesthesia. Mepivacaine, 2%, is frequently used for epidural anesthesia and produces a level of blockade similar to that of bupivacaine, 0.5%. The purpose of this study was to examine the sensory blockade in the sacral region induced by ropivacaine with that induced by mepivacaine administered in the lower thoracic epidural space.

METHODS: Eighteen adults undergoing lower thoracic epidural anesthesia (thoracic 11/12 interspace) were studied in a double-blind fashion. Patients were assigned to one of two groups: those who received 2% mepivacaine, 18 ml (group M; n = 9), and those who received 1% ropivacaine, 12 ml (group R; n = 9). The cephalad levels of sensory blockade to cold, pinprick, and touch in the L2, S1, and S3 dermatomes were assessed at 10, 20, and 35 min after injection.

RESULTS: There were no differences in the cephalad levels of sensory block to cold (T4 [range, T4-T2] and T4 [range, T6-T2]), pinprick (T4 [range, T6-T4] and T4 [range, T6-T4]), or touch (T6 [range, T6-T4] and T6 [range, T6-T4]) between group M and group R respectively, at 35 min (P > 0.05). In the L2 and S3 dermatomes, there were no significant differences in the numbers of patients who obtained sensory block to cold or pinprick at 20 and 35 min after study drug administration. However, in the S1 dermatome, significantly higher numbers of patients in group R obtained sensory block to cold at 20 and 35 min after study drug administration than in group M (8 and 0; 9 and 0; P = 0.001 and P < 0.001; 20 min and 35 min after administration, respectively). Also in the S1 dermatome, significantly higher numbers of patients in group R obtained sensory block to pinprick at 20 and 35 min after study drug administration than in group M (6 and 0; 9 and 0; P = 0.027 and P < 0.001; 20 min and 35 min after administration, respectively). A significantly higher number of patients in group R had sensory block to touch in the S3 dermatome at 35 min (7 and 2; group R and group M, respectively; P = 0.01).

CONCLUSION: Ropivacaine, 1%, administered in the lower thoracic epidural space, induces sensory blockade to cold and pinprick in the S1 dermatome more frequently than 2% mepivacaine.