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.