groups. Temperatures in the control newborns ranged from 35.6 to 37.71C; those in the warmed groups ranged from 37.1 to 37.21C. Maternal temperatures at the end of cesarean delivery for controls were from 35.6 to 36.41C; intervention group temperatures ranged from 35.5 to 37.11C. Umbilical cord blood gas pH values were lower in control groups in all studies compared to the pH values obtained from warmed mothers. In 4 studies, maternal shivering in control women were 60%, 33%, 47%, and 64%; in the warmed patients, rates were 13%, 31%, 27%, and 14%, respectively. Trials are needed to compare the benefits of pre- operative and perioperative forced air and IV fluid warming and to determine whether the benefits of reduced wound infections, reduced hospital stays, and reduced hospital costs seen in other surgical patients can be duplicated in women undergoing cesarean delivery. Risk Factors for Failed Conversion of Labor Epidural Analgesia to Cesarean Delivery Anesthesia: A Systematic Review and Meta-Analysis of Observational Trials M.E. Bauer, J.A. Kountanis, L.C. Tsen, M.L. Greenfield, and J.M. Mhyre (Int J Obstet Anesth. 2012;21(4):294–309) Department of Anesthesiology, University of Michigan Health System, Ann Arbor, MI Copyright r 2013 by Lippincott Williams & Wilkins DOI: 10.1097/01.aoa.0000436297.31016.18 Topics: Regional Anesthesia for Cesarean Section, Anesthetic Complications N euraxial anesthesia is generally preferred over general anesthesia for cesarean delivery (CD), and conversion of labor epidural analgesia to epidural anesthesia for CD is used to limit the use of general anesthesia in obstetrics. However, conversion from labor epidural analgesia to epidural anes- thesia for CD sometimes fails. Understanding the risk factors for failed epidural conversion may assist anesthesiologists in identifying replacing at-risk epidural catheters. This review and meta-analysis was performed to evaluate the evidence for potential risk factors associated with failed conversion of labor epidural analgesia to CD anesthesia. OvidST, PubMed, and EMBASE databases were searched to identify cohort, case-control, and cross-sectional observational studies published between 1979 and May 2011 that reported failed conversion of labor epidural analgesia to CD epidural anesthesia. Data were extracted from studies that included risk factors for conversion as well as studies that included a failure rate without assessing risk factors. Data from that latter category were used only for determi- nation of an overall failure rate. Data from the former studies were combined in a random-effects meta-analysis to evaluate the evidence for each potential risk factor. From 1450 trials screened, 13 observational trials involving 8628 women were included. CDs performed under general anesthesia with a preexisting labor epidural catheter in place occurred in 5% of patients. Need for a second anesthetic (neuraxial or general anesthesia) at the time of CD occurred in 7.7% of women. In addition, 10.7% of patients with a preexisting labor epidural catheter required some form of supplementation, such as intravenous or inhalational sedation, during CD. Among women who needed 1 or more clinician-administered top-ups during labor, the rate of failed conversion increased from 4.6% for those not requiring top- ups to 16.4%. A study that examined the effect of the urgency of CD on conversion failure reported that 18 of 27 attempts (25%) to convert eventually required general anesthesia for CDs classified as category 1 compared with 35 of 505 (7%) for category 2, and 11 of 452 (2.4%) for category 3 CDs. The odds ratio of urgency as a risk factor for epidural failure was 40.4. The rate of conversion from epidural analgesia to general anesthesia was significantly increased when a non- obstetric anesthesiologist versus an obstetric anesthesiologist was providing the anesthesia for CD of the patient’. Average failure rates for nonobstetric and obstetric anesthesiologists were 7.2% and 1.6%, respectively, for an odds ratio of 4.56. Studies that reported on body mass index (BMI) or weight as a risk factor found no association between failed epidural conversion and BMI; the standardized mean difference in weight also did not differ between women with successful or failed conversion. No difference in the duration of labor epidural analgesia before conversion for CD was found between women with successful versus failed conversion of epidural analgesia to surgical anesthesia. For 2 studies examining the number of patients with successful conversion of combined spinal-epidural analgesia versus epidural anal- gesia, random-effects meta-analysis yielded insufficient evi- dence to suggest that either technique is more successful than the other in this regard. Cervical dilation at the initiation of epidural labor analgesia was not associated with failed epi- dural conversion. Of 7 potential risk factors investigated in this meta- analysis, an increased risk of failed epidural conversion for CD was found for the following factors: increased number of clinician-administered top-ups during labor, greater urgency of CD, and anesthetic care provided by a nonobstetric anesthesiologist. Evidence for the other 4 risk factors (BMI or weight, cervical dilation, duration of labor analgesia, and CSE vs. epidural) was insufficient to support an association with failed conversion. Additional high-quality studies are required to assess other potential risk factors for failed con- version of labor epidural analgesia to CD anesthesia. COMMENT Neuraxial analgesia is commonly utilized to alleviate labor pain, and its popularity is related to its efficacy and safety. Women can obtain almost complete relief from the pain of labor. From the anesthesiologist’s perspective, because a catheter is threaded into the epidural space, it is also a versatile technique. During the earlier stages of labor, dilute solutions of local anesthetic can be used to achieve analgesia. As labor progresses, a more concentrated sol- ution of local anesthetic can be used, or an adjunct, such as an opioid, can be added. In addition, the epidural catheter can be utilized to maintain a low dermatome level of Editorials and Reviews Obstetric Anesthesia Digest  Volume 33, Number 4, December 2013 186 | www.obstetricanesthesia.com r 2013 Lippincott Williams & Wilkins