The primary action of epidural fentanyl after cesarean delivery is via a spinal mechanism.
We tested the hypotheses that the primary mechanism of action of epidural fentanyl after cesarean delivery is spinal and that very small dose epidural bupivacaine with epinephrine enhances this effect. After elective cesarean delivery, 100 parturients were randomized in a double-blinded design to four groups. Group I and II patients received a continuous 12 mL/h epidural infusion of bupivacaine 0.015% with epinephrine 1 microg/mL for 48 h and Groups III and IV received a 12 mL/h saline epidural infusion instead. Fentanyl 20 microg/mL was administered via a patient-controlled analgesia device either into the epidural infusion (Groups I and IV) or IV (Groups II and III). When compared to patients receiving epidural fentanyl, those receiving IV fentanyl required larger mean infused and total dose of fentanyl (P < 0.0001), reported more pain (P < 0.001), and had a more frequent incidence of excessive sedation (P < 0.01), nausea (P < 0.01), and vomiting (P < 0.01). Plasma concentrations of fentanyl were larger for Group II and III than for Groups I and IV (P < 0.001) at 24 and 48 h. Our results support the hypothesis that the primary mechanism of analgesia of epidural fentanyl after cesarean delivery is spinal. Our data also show that the total required dose of epidural, but not IV, fentanyl is reduced by very small dose epidural bupivacaine and epinephrine (Group I versus Group IV, P < 0.02 and Group II vs Group III, not significant).


CONCLUSIONS
Fentanyl administered epidurally to parturients after cesarean delivery has a primarily spinal mechanism of action and this effect is enhanced by very small dose epidural bupivacaine and epinephrine.
Cohen
Shaul
S
Department of Anesthesiology, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903, USA. cohensh@umdnj.edu
Pantuck
Carol B
CB
Amar
David
D
Burley
Elizabeth
E
Pantuck
Eugene J
EJ
D000767:Anesthesia, Epidural; D000773:Anesthesia, Obstetrical; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D002585:Cesarean Section; D005260:Female; D005283:Fentanyl / Q000009:adverse effects / Q000097:blood / Q000494:pharmacology*; D006801:Humans; D011247:Pregnancy; D013116:Spinal Cord / Q000187:drug effects*
D018686:Anesthetics, Intravenous; D005283:Fentanyl