Advances in labor analgesia

Abstract

The pain of childbirth is arguably the most severe pain most women will endure in their lifetimes. The pain of the early first stage of labor arises from dilation of the lower uterine segment and cervix. Pain from the late first stage and second stage of labor arises from descent of the fetus in the birth canal, resulting in distension and tearing of tissues in the vagina and perineum. An array of regional nerve blocks, systemic analgesic, and nonpharmacologic techniques are currently used for labor analgesia. Nonpharmacologic methods are commonly used, but the effectiveness of these techniques generally lacks rigorous scientific study. Continuous labor support has been shown to decrease the use of pharmacologic analgesia and shorten labor. Intradermal water injections decrease back labor pain. Neuraxial labor analgesia (most commonly epidural or combined spinal-epidural) is the most effective method of pain relief during childbirth, and the only method that provides complete analgesia without maternal or fetal sedation. Current techniques commonly combine a low dose of local anesthetic (bupivacaine or ropivacaine) with a lipid soluble opioid (fentanyl or sufentanil). Neuraxial analgesia does not increase the rate of cesarean delivery compared to systemic opioid analgesia; however, dense neuraxial analgesia may increase the risk of instrumental vaginal delivery.

Keywords: childbirth pain; epidural analgesia; labor analgesia; neuraxial analgesia.

Figure 1

Comparison of pain scores using the McGill Pain Questionnaire obtained from women during labor and from patients in general hospital clinics and an emergency department. The pain rating index (PRI) represents the sum of the rank values for all words chosen from 20 sets of pain descriptions. From Melzack R. The myth of painless childbirth [The John J. Bonica Lecture]. Pain. 1984;19(4):321–337. Copyright © 1984. This figure has been reproduced with permission of the International Association for the study of Pain^® (IASP^®). The figure may not be reproduced for any other purpose without permission.

Figure 2

Transmission of labor pain. Labor pain has a visceral component and a somatic component. Noxious impulses from the uterus and cervix follow afferent sensory-nerve fibers that accompany sympathetic nerves, traveling through the paracervical region and the pelvic and hypogastric plexus to enter the lumbar sympathetic chain and the dorsal horn of the spinal cord through the white rami communicantes of the T10, T11, T12, and L1 spinal nerves. Noxious impulses from the vagina and perineum travel via the pudendal nerve to enter the spinal cord at S2 to S4. Reprinted with permission from Eltzschig HK, Lieberman ES, Camann WR. Regional anesthesia and analgesia for labor and delivery. N Eng J Med. 2003;348(4):319–332. Copyright © 2003 Massachusetts Medical Society. All rights reserved.

Figure 3

Placement of intradermal water blocks: 4 intradermal injections of 0.05 to 0.1 mL of sterile water to form 4 small blebs over each posterior superior iliac spine and 3 cm below and 1 cm medial to each spine. The exact locations of the injections do not appear to be critical to the block success. Reprinted with permission from Simkin P, Bolding A. Update on nonpharmacologic approaches to relieve labor pain and prevent suffering. J Midwifery Womens Health. 2004;49(6):489–504. Copyright © 2004 Elsevier.

Figure 4

Cross-sectional view of the combined spinal-epidural (CSE) needle-through-needle technique. The large-gauge epidural needle is sited in the epidural space and the small-gauge spinal needle is passed through the epidural needle and punctures the dura to site in the subarachnoid space. Reprinted with permission from Birnbach DJ, Ojea LS. Combined spinal-epidural (CSE) for labor and delivery. Int Anesthesiol Clin. 2002;40(4):27–48. Copyright © 2002 Lippincott Williams & Wilkins.