Differential epidural block. Does the choice of local anesthetic matter?

BACKGROUND AND OBJECTIVES: It is well established that spinal anesthesia results in a differential block to the sensations of pinprick and cold temperature discrimination. However, the existence of differential block during epidural anesthesia has not always been accepted. Recently, it has been shown that lumbar epidural anesthesia with chloroprocaine and lidocaine produces a differential block to pinprick and cold sensation. The purpose of this study was to determine if the choice of local anesthetic used for epidural anesthesia has any influence on the relative levels of anesthesia, analgesia, and cold sensation.

METHODS: The authors studied nine healthy subjects; each was studied three times and received one of three local anesthetics (0.75% bupivacaine, 2% lidocaine, and 3% chloroprocaine) via an epidural catheter placed into the second or third lumbar epidural space. The authors tested the following modalities compared to an unblocked dermatome: anesthesia, loss of sensation to pinprick; analgesia, loss of an equally sharp sensation to pinprick; and cold sensation, loss of cold sensation to alcohol.

RESULTS: Twenty minutes after injection of the local anesthetic, zones of differential sensory block existed for all three agents tested. Anesthesia and analgesia were the most caudad and cephalad, respectively, while loss-to-cold sensation was found to be between these two levels. There was no significant difference in the dermatomal level achieved among the three local anesthetics tested. Sensory testing data observed 10 minutes later showed that no significant change had occurred.

CONCLUSIONS: This study reaffirms the existence of differential sensory block during epidural anesthesia and establishes that the observed differential block appears to be independent of the local anesthetic used.