The effect of bupivacaine with fentanyl temperature on initiation and maintenance of labor epidural analgesia: a randomized controlled study

•Warming local anesthetic agents alters their physiochemical properties.•Bupivacaine with fentanyl at body (37°C) and room (20°C) temperature were compared.•Warmed bupivacaine with fentanyl results in faster labor analgesia onset.•Warmed bupivacaine with fentanyl results in improved initial analgesia.•Hourly boluses with warmed bupivacaine with fentanyl did not alter ongoing analgesia.

BackgroundLabor epidural analgesia is highly effective, but can be limited by slow onset and incomplete blockade. The administration of warmed, compared to room temperature, bupivacaine has resulted in more rapid onset epidural anesthesia. We hypothesized that the administration of bupivacaine with fentanyl at 37°C versus 20°C would result in improved initial and ongoing labor epidural analgesia.MethodsIn this prospective, randomized, doubled blinded study, 54 nulliparous, laboring women were randomized to receive epidural bupivacaine 0.125% with fentanyl 2 μg/mL (20 mL initial and 6 mL hourly boluses) at either 37°C or 20°C. Pain verbal rating scores (VRS), sensory level, oral temperature, and side effects were assessed after epidural loading (time 0), at 5, 10, 15, 20, 30, 60 min, and at hourly intervals. The primary outcome was the time to achieve initial satisfactory analgesia (VRS ⩽3). Secondary outcomes included ongoing quality of sensory blockade, body temperature and shivering.ResultsThere were no differences between groups in patient demographics, initial pain scores, cervical dilatation, body temperature or mode of delivery. Epidural bupivacaine at 37°C resulted in shorter mean (±SD) analgesic onset time (9.2 ± 4.7 vs. 16.0 ± 10.5 min, P = 0.005) and improved analgesia for the first 15 min after initial bolus (P = 0.001–0.03). Although patient temperature increased during the study (P < 0.01), there were no differences between the groups (P = 0.09). Six (24%) and 10 (40%) patients experienced shivering in the 37°C and 20°C groups, respectively (P = 0.23).ConclusionsThe administration of epidural 0.125% bupivacaine with fentanyl 2 μg/mL at 37°C versus 20°C resulted in more rapid onset and improved labor analgesia for the first 15 min. There was no evidence of improved ongoing labor analgesia or differences in side effects between groups.