Epidural fentanyl produces labor analgesia by a spinal mechanism

Background: The purpose of this study was to determine if epidural fentanyl produces analgesia in laboring patients by a primary spinal or supraspinal action. Methods: Fifty-four parturients were randomized to receive epidural 0.125% bupivacaine plus one of three treatments: epidural saline-intravenous saline, epidural fentanyl (20 mu g/h)-intravenous saline, or epidural saline-intravenous fentanyl (20 mu g/h). The study treatments were administered by continuous infusion, whereas epidural bupivacaine use was patient controlled. Results: Epidural bupivacaine use was significantly reduced by epidural(11.5 +/- 4.6 ml/h) but not by intravenous fentanyl (15.9 +/- 4.5 ml/h) compared with saline control (16 +/- 5.9 ml/h). Analgesia characteristics and side effects mere similar among groups. Conclusions: Low-dose epidural infusions of fentanyl produce labor analgesia by a primary spinal action.