Saline-anesthetic interval and the spread of epidural anesthesia.

PURPOSE To examine the effect of modifying the interval between administration of saline used during the loss of resistance (LOR) method and local anesthetic on epidural anesthetic level and its quality. METHODS Seventy-three patients who received thoracic epidural anesthesia were randomly allocated into three groups; the 2, 5 and 10 min groups, according to the interval between the administration of saline and 8 ml mepivacaine 1.5%. Fifteen minutes after the mepivacaine injection, the dermatome level of hypesthesia was determined by an individual blinded to the interval. RESULTS When the saline-anesthetic interval was prolonged, the hypesthetic levels for coldness and pinprick were decreased. The number of spinal segments with hypesthesia for coldness were 15 [12-20]#, 12.5 [10.5-22.5]## and 10.5 [6.5-15.5]### in the 2, 5 and 10 min groups, respectively (median [range], # P < 0.05 vs the 5 min group, ## P < 0.05 vs the 10 min group, ### P < 0.05 vs the 2 min group). The number of spinal segments with hypesthesia for pinprick were 13.5 [11-18]#, 11 [7.5-20.5]## and 10 [5.5-13]### in the 2, 5 and 10 min groups, respectively. There were differences in all groups between the number of segments with hypesthesia for coldness and pinprick elicited. CONCLUSION The interval between the administration of saline and local anesthetic alters the anesthetic level and quality of epidural analgesia.