Delayed onset of epidural anesthesia in patients with back pain

Onset and completeness of anesthesia were compared in 15 patients with back pain or sciatica and in 10 patients without back pain given lumbar epidural anesthesia with 20 to 25 ml of 1.5% mepivacaine, 80 mg of methylprednisolone, and 1:200,000 epinephrine. Sensory block was complete within 30 minutes in patients without back pain. Eleven of 15 (73%) patients with back pain had delayed onset of anesthesia ranging from 35 to 95 minutes. The difference between the two groups was statistically significant (p < 0.001). When there was a delay, the affected nerve roots were blocked 10 to 70 minutes after the contralateral unaffected roots. Differences in time of onset between affected nerves and contralateral nerves were also significant (p < 0.01). The nerve roots involved, as determined from the myelogram or the electromyogram, or those adjacent to them, were the roots with delayed onset of block. Any effect of the steroid on nerve blockade was ruled out as there was solid anesthesia in patients without back pain.