Effect of Local Anesthetic Solution at Different Temperatures for Epidural Labor Analgesia on Intrapartum Fever: A Randomized Clinical Trial

BACKGROUND: Whether heating local anesthetic solutions to core body temperature (37°C) for epidural labor analgesia reduces intrapartum fever incidence remains undefined in the current literature. METHODS: This double-blind randomized controlled trial (RCT) enrolled 220 nulliparous parturients (18-35 years, American Society of Anesthesiologists [ASA] physical status II, term singleton pregnancy). Participants were randomized to receive epidural labor analgesia with 0.075% ropivacaine + 0.5 µg/mL sufentanil at 37°C (warmed group) or 22°C (room-temperature group). Epidurals were placed at L3-L4 with a test dose of 3 mL of 1.5% lidocaine at room temperature, followed by programmed bolus epidural analgesia (initial 10 mL, 10 mL/h) and patient-controlled epidural analgesia (PCEA) 5 mL (30-minute lockout). Tympanic temperature was measured every 30 minutes from epidural initiation to delivery, defining intrapartum fever as ≥38°C. The primary outcome was fever incidence, on which the power analysis was based, and also maximum temperature and shivering. Secondary outcomes comprised analgesia onset, block level, labor durations, neonatal Apgar scores, umbilical cord blood pH and BE, and maternal adverse events. RESULTS: A total of 220 parturients were included (warmed group, n = 110; room-temperature group, n = 110). The warmed group had a lower intrapartum fever incidence (15.5% [17/110] vs 30.9% [34/110], relative risk [RR] 0.5 [95% confidence interval {CI}, 0.298-0.840]; P = .007); however, the reduction of 49.8% did not reach the preset clinically meaningful difference of 60% reduction proposed in the power analysis. The maximum body temperature was also lower in the warmed group: median (interquartile range [IQR]) 37.4 (IQR, 37.2-37.7) °C vs 37.6 (IQR, 37.3-38.0) °C, median difference -0.2 (95% CI, -0.3 to -0.1) °C (P = .006). Shivering incidence was not different between groups (10.9% [12/110] vs 14.5% [16/110]; P = .418). No statistically significant differences were observed between groups in any of the secondary outcomes assessed, including block characteristics, local anesthetic consumption, labor duration, neonatal outcomes, and maternal adverse events. CONCLUSION: Although we found a 50% reduction in the incidence of temperature rise using warmed (37°C) local anesthetics for epidural labor analgesia, this did not reach our preset threshold of 60% reduction.