By infusing a higher concentration (100 μg/min), we subject the mother and fetus to a much higher dose of phenylephrine, with significant effects on maternal HR and CO (up to a 20% reduction). Future investigation is required to determine whether this reduction in maternal CO has detrimental effects when providing anesthesia for an emergency cesarean delivery for a compromised fetus.

We have used the technique of randomized, double-blind sequential allocation to compare the minimum local analgesic concentrations (MLAC) of epidural bupivacaine and ropivacaine for women in the first stage of labour. The test bolus was 20 ml of local anaesthetic solution. The concentration was determined by the response of the previous woman to a higher or lower concentration of local anaesthetic, according to up-down sequential allocation. Efficacy was assessed using a 100-mm visual analogue pain score (VAPS). The test solution had to achieve a VAPS of 10 mm or less to be judged effective. For bupivacaine, MLAC was 0.093 (95% CI 0.076-0.110)% w/v, and for ropivacaine, 0.156 (95% CI 0.136-0.176)%w/v (P < 0.0001, 95% CI difference 0.036-0.090). The analgesic potency of ropivacaine was 0.60 (0.47-0.75) relative to bupivacaine. Claims for reduced toxicity and motor block must be considered with differences in analgesic potency in mind.

No abstract

Labor initiates one of the most intensely painful episodes in a woman's life. Opioids are used to provide analgesia with substantial interindividual variability in efficacy. μ-Opioid receptor (μOR, OPRM1) genetic variants may explain differences in response to opioid analgesia. We hypothesized that OPRM1 304A/G polymorphism influences the median effective dose (ED 50 ) of intrathecal fentanyl via combined spinal-epidural for labor analgesia. Nulliparous women were prospectively recruited around 35 weeks gestation (n = 224), and genotyped for 304A/G polymorphism. Those requesting neuraxial labor analgesia were enrolled in one of the two double-blinded trials: up-down sequential allocation (SA, n = 50) and a separate confirmatory random-dose allocation trial (RA, n = 97). Effective analgesia from intrathecal fentanyl was defined by ⩾ 60 min analgesia with verbal rating score ≤1 (scale 0-10) and was compared between μOR 304A homozygotes (Group A) and women carrying at least one 304G allele (Group G). OPRM1 304G allele frequency f(−) was 0.18. Using SA, intrathecal fentanyl ED 50 was 26.8 μg (95% CI 22.7-30.9) in Group A and 17.7 μg (95% CI 13.4-21.9) in Group G (p < 0.001; 304A homozygosity increased the ED 50 1.5-fold). RA confirmed that 304A homozygosity significantly increases intrathecal fentanyl ED 50 (27.4 μg in Group A and 12.8 μg in Group G [p < 0.002; 2.1-fold]). We demonstrate for the first time that the μOR 304G variant significantly reduces intrathecal fentanyl ED 50 for labor analgesia, suggesting women with the G variant may be more responsive to opioids and require less analgesic drugs. These Conflict of interestNone of the authors presents any commercial association or other issues that might pose a conflict of interest. Financial disclosures