“…After epidural injection, there is rapid uptake of fentanyl into epidural blood vessels as well as into the spinal cord, and blood concentrations obtained after lumbar epidural infusion 8:2,15-17 have often been in the range reported as being effective analgesic blood concentrations with systemic infusions. Is-E~ Recent studies have questioned whether the analgesic efficacy of epidural fentanyl is secondary to systemic absorption and recirculation to the central nervous system through the blood-brain bartier, 12,15,16,23 or is mediated by a direct spinal mechanism. 25 If the former were the case, then there may be no advantage to the epidural route.…”