Effect of epidural epinephrine on the minimum local analgesic concentration of epidural bupivacaine in labor.
BACKGROUND
The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration in a 20-ml volume for epidural analgesia in the first stage of labor. The aim of this study was to determine the local anesthetic-sparing efficacy of epidural epinephrine by its effect on the MLAC of bupivacaine.


METHODS
In this double-blind, randomized, prospective study, 70 parturients who were at 7 cm or less cervical dilation and who requested epidural analgesia were allocated to one of two groups. After lumbar epidural catheter placement, 20 ml bupivacaine (n = 35) or bupivacaine with epinephrine 1:300,000 (n = 35) was administered. The concentration of bupivacaine was determined by the response of the previous patient in that group to a higher or lower concentration using up-down sequential allocation. Analgesic efficacy was assessed using 100-mm visual analog pain scores, with 10 mm or less within 30 min defined as effective.


RESULTS
The MLAC of bupivacaine alone was 0.091% wt/vol (95% confidence interval, 0.081-0.102). The addition of epinephrine 1:300,000 (66.7 microg) resulted in a significant reduction (P < 0.01) in the MLAC of bupivacaine to 0.065% wt/vol (95% confidence interval, 0.047-0.083). The lowest maternal blood pressure was significantly lower in the bupivacaine-epinephrine group (P = 0.03). There were statistically significant reductions in fetal heart rate (P = 0.011) in the bupivacaine-epinephrine group that were not clinically significant.


CONCLUSIONS
The addition of epidural epinephrine 1:300,000 (66 microg) resulted in a significant 29% reduction in the MLAC of bupivacaine. Coincident reductions in fetal heart rate and maternal blood pressure were also observed that were not clinically significant.
Polley
Linda S
LS
Department of Anesthesiology, Women's Hospital, University of Michigan Health System, Ann Arbor, Michigan 48109-0211, USA. lpolley@umich.edu
Columb
Malachy O
MO
Naughton
Norah N
NN
Wagner
Deborah S
DS
van de Ven
Cosmas J M
CJ
D000328:Adult; D015360:Analgesia, Epidural; D016362:Analgesia, Obstetrical; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000493:pharmacokinetics*; D002045:Bupivacaine / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004311:Double-Blind Method; D004837:Epinephrine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D005260:Female; D006340:Heart Rate, Fetal / Q000187:drug effects; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D010147:Pain Measurement; D011247:Pregnancy; D011446:Prospective Studies; D014662:Vasoconstrictor Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*
D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D002045:Bupivacaine; D004837:Epinephrine