title: Effect of epidural epinephrine on the minimum local analgesic concentration of epidural bupivacaine in labor.
abstract: 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.
authors: Department of Anesthesiology, Women's Hospital, University of Michigan Health System, Ann Arbor, Michigan 48109-0211, USA. lpolley@umich.edu
authors: Linda S
authors: LS
authors: Polley
authors: Malachy O
authors: MO
authors: Columb
authors: Norah N
authors: NN
authors: Naughton
authors: Deborah S
authors: DS
authors: Wagner
authors: Cosmas J M
authors: CJ
authors: van de Ven
mesh_terms: 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*
chemical_list: D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D002045:Bupivacaine; D004837:Epinephrine