Fig. 4. Influence of the hour of injection on the duration (mean ± SD) of epidurally administered ropivacaine during labor. Group 1 (01:00–07:00 h), group 2 (07:00–13:00 h), group 3 (13:00–19:00 h), group 4 (19:00–01:00 h). *P < 0.01 versus groups 1 and 4. From Debon et al 38; used with permission.