Background: The addition of epinephrine (2 micro g.ml-1) to a thoracic epidural infusion of an opioid-local anesthetic mixture improves analgesia. Here, we studied whether epinephrine could improve analgesia also at lumbar level, when added to an epidural infusion of a low-dose ropivacaine-fentanyl mixture after arterial bypass surgery of the legs.
Methods: Patients in group RFE (n = 21) received a postoperative epidural infusion containing ropivacaine (1 mg.ml-1), fentanyl (2 micro g.ml-1), and epinephrine (2 micro g.ml-1). Patients in group RF (n = 25) received a similar infusion without epinephrine. The infusion speed was 1 ml.10 kg-1. h-1. The infusion was scheduled for 48 h.
Results: Epinephrine did not reduce the need for rescue pain medication. Visual analog scale scores (VAS) for pain at rest were low and similar in the groups. Pain intensity was stronger during leg movement [mean VAS 1.5-2.6 (range 0-9)], but it was not affected by the coadministration of epinephrine. The groups did not differ concerning frequency and severity of side-effects. Epinephrine did not reduce fentanyl plasma concentrations. Ropivacaine concentrations were slightly lower in group RFE only in the samples 6 h from the start of the infusion, but not anymore on the first and second postoperative day.
Conclusion: In the dosage used here, epinephrine did not improve epidural lumbar analgesia. Different distances from the epidural application site to the alpha2-adrenergic receptors of the spinal cord, and differing epinephrine dose requirements may explain why epinephrine as an additive improves epidural analgesia at thoracic, but not at lumbar level.