It depends on many factors, which may assess a doctor.
But we must bear in mind that promedol can be introduced only once, so it's best to enter during strong contractions, and when the cervix has opened well, since its effect lasts 1-1.5 hours. Promedol not completely remove the pain, but reduces the severity of the pain it feels differently.
During epidural pain is removed completely, pain can be added through a thin catheter with the increasing pain.
Epidural make only a very experienced anesthesiologist, who are fluent in this method, so this complication, as spinal cord injury, is practically impossible. Headaches after childbirth is a rare, but there are complications, which will soon pass.