Why epidurals do not always work.

The overwhelming majority of epidural catheters placed for labor provide satisfactory analgesia. There are, however, times when the catheter is not sited within the epidural space correctly, the patient's neuraxial anatomy is problematic, or a patient's labor progresses more quickly than expected by the anesthesiologist, and the epidural block does not set up on time. In this article, the basics of neuraxial labor analgesia, the causes of its failure, and the strategies anesthesiologists employ to rescue poorly functioning catheters are reviewed.