Labor epidural analgesia onset time and subsequent analgesic requirements: a prospective observational single-center cohort study

Background: We investigated the correlation between lumbar epidural analgesia onset time and pain intensity at 60 and 120 min after initiation. Methods: We conducted a prospective observational study of nulliparous women receiving lumbar epidural analgesia (initial bolus 15 mL bupivacaine 0.1% with fentanyl 3.33 μg/mL), followed by patient-controlled epidural analgesia (PCEA). The measured variable was lumbar epidural analgesia onset time (time to pain numerical rating score ≤3). Secondary outcomes were pain score at 60 and 120 min and at full dilatation; and analgesic requirements through the labor. Results: One-hundred-and-five women were eligible for analysis. There was a significant correlation between lumbar epidural analgesia onset time and pain intensity at 60 min (Spearman's R²=0.286, P=0.003), but not at 120 min (R²=0.030, P=0.76). Women who requested more PCEA boluses during the first 120 min had a longer lumbar epidural analgesia onset time (R²=0.321, P=0.001) and reported higher pain scores at 60 min (R²=0.588, P <0.001) and at 120 min (R²=0.539, P <0.001). Women who reported higher pain scores at 60 min had more pain at 120 min (R²=0.47, P <0.001) and higher analgesic consumption during labor (R²=0.403, P <0.001). Women who were at a greater cervical dilatation at 60 and 120 min had higher pain scores at the same time point (R²=0.259, P=0.008 and R²=0.243, P=0.013 respectively). Conclusion: There was a correlation between the onset time of lumbar epidural analgesia during labor and the pain score 60 min later but this had disappeared by 120 min.