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Physiology of Labor and Delivery

Pain of Parturition

Relief of Labor Pain (Not Related to Medication) Hypnosis

Psychoanalgesia Natural childbirth Psychoprophylaxis Leboyer Technique Acupuncture

Transcutaneous Electrical Nerve Stimulation Water birth

Labor and delivery are complex processes involving different organ systems orchestrated in expelling the fetus and placenta from the mother. This process has been divided into three spe- cific stages:

1. The first stage starts from the latent phase of labor (pro- gressive cervical dilatation associated with regular uterine contraction) and terminates at the time of full dilatation of the cervix.

2. The second stage starts from full dilatation of the cervix and terminates at the time of the delivery of the infant.

3. The third stage starts from delivery of the infant and termi- nates at the time of expulsion of the placenta.

Pain of Parturition

Pain during the first stage of labor is mediated through the afferent nerve supply of the uterus via the sympathetic nerve, which ultimately reaches the T10-L1 segments of the spinal

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cord. The first stage of labor pain has been described as referred pain. This can be explained by the common neuronal pool supplying both the uterus and the anterior abdominal wall (Fig. 6-1). In summary, pain during the first stage of labor is mediated by the T10-L1 spinal segments, whereas second- stage pain is carried by the S2, S3, and S4 spinal segments.

The nerves from the uterus together with other autonomic nerve fibers from the cervix form the interior hypogastric plexus; fibers from this plexus traverse along the iliac vessels as the right and left hypogastric nerves. These nerves ulti- mately communicate with the superior hypogastric nerve and reach the sympathetic chain either directly or via the aortic plexus. These finally reach the spinal cord via the posterior nerve root ganglion. Some of the nerve fibers from the ovary, uterine ligaments, and fallopian tubes travel via ovarian nerves and ultimately reach the spinal cord via the aortic plexus and sympathetic chain. The nerves in the spinal cord relay to

T L

10 11 12 1

2 3 4

S

Figure 6-1. Pain pathways for the first and second stages of labor.

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neurons of the posterior horn cells and ultimately reach the central nervous system via the lateral spinothalamic tract.

Pain during the second stage of labor follows a different pathway from the first stage of labor. Pain for the second stage of labor is carried by the pudendal nerve (S2, S3, S4). This nerve originates from the sacral plexus and accompanies the puden- dal vessels across the ischial spine where the nerve can be blocked.

Relief of Labor Pain

(Not Related to Medication)

The McGill pain questionnaire ranks labor pain in the upper part of the pain scale between that of cancer pain and ampu- tation of a digit1(Fig. 6-2). Although systemic medications and

50

40

30

20

10 Causalgia

Labor pain

Clinical pain syndromes

Pain after accidents PAIN (PRI*)

SCORES

Amputation of Digit

Bruise Fracture Cut Laceration Sprain Primiparas

(No Training)

Primiparas

(Prepared Childbirth Training)

Primiparas

(Trained and Untrained)

Cancer Pain

(Non-terminal)

Phantom Limb Pain Post-Herpetic Neuralgia Toothache Arthritis Chronic Back Pain

Figure 6-2. Comparison of pain scores by using the McGill pain questionnaire. (Adapted from Melzack R: Pain 1984;

19:321.)

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regional anesthetics have become popular in recent years, other techniques that do not involve medication have also been tried in different centers with varied success.

These techniques include hypnosis, psychoanalgesia (natural childbirth and psychoprophylaxis), the Leboyer technique, acupuncture, and transcutaneous electrical nerve stimulation (TENS).

Hypnosis

Hypnosis has been used for relief of labor pain for a long time. The advantages of this technique include minimal maternal and fetal physiological interference; however, the major disadvantage is related to its relatively small success rate.

Psychoanalgesia Natural Childbirth

Dick-Read in 1940 originated this concept and tried to make it popular.2 He explained the mechanism of labor pain in relation to anxiety and fear and preached a fearless approach to labor to minimize the pain.

Psychoprophylaxis

Lamaze is the originator of this psychoanalgesic technique, and it became very popular among women who tried to avoid medications during labor and delivery. This technique involves a proper education of parturients regarding “positive”

conditioned reflexes. The advantages of this procedure include the avoidance of any medications, which disturb the maternal physiology, as well as avoidance of fetal depression from nar- cotics. However, the success rate of this technique varies con- siderably, and parturients may request systemic medications or regional analgesia when using this technique. Interestingly, a study shows that parturients prepared for delivery under psychoprophylaxis need less analgesia than do unprepared parturients.3

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Leboyer Technique

In 1975 the French obstetrician Leboyer described “birth without violence.”4According to the author the psychological birth trauma of the neonate can be reduced by avoiding noise, bright lights, and other stimulation of the delivery room. Hence Dr. Leboyer believes in delivering the baby in a silent semidark room and also avoiding stimulation of the newborn immediately after the delivery. In Boston Hospital for Women, Leboyer delivery was popular among a few obstetricians. Parturients received either systemic medication, local anesthetic via the epidural route, or no medication.

Anesthesiologists and neonatologists faced a few problems: (1) problems with neonatal temperature and (2) improper lighting for adequate evaluation of the babies. This technique is seldom used in Brigham and Women’s Hospital at the present time.

Acupuncture

Acupuncture techniques have been used in China both for surgery as well as for pain relief; however, there is no evidence of this technique being used for pain relief of labor and deliv- ery. Wallis and colleagues used this technique in parturients without adequate success.5

Transcutaneous Electrical Nerve Stimulation

TENS has been used for chronic pain therapy as well as relief of acute postoperative pain. Although the mechanism is not exactly known, the different hypotheses that have been put forward are (1) modulation of the pain impulse reaching the substantia gelatinosa and (2) liberation of endogenous opioids.6,7

TENS has been used for the relief of labor pain with variable success. Skin electrodes of conductive adhesive are placed over the T10-L1 spinal region bilaterally; TENS can also be applied in the sacral area during the second stage of labor (Fig. 6-3). Because of its inconsistent success, this technique has never become popular in this country.

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Water Birth

Another natural childbirth option that has become popular is water birth. Water birth provides a calm, relaxing atmos- phere for both the expectant mother and her newborn.

Ultimate success from the techniques described above vastly depends upon the parturients’ own motivation; hence the success of these methods varies widely, and thus these modes have never been universally accepted.

References

1. Melzack R: The myth of painless childbirth. Pain 1984; 19:32.

2. Dick-Read G: Childbirth Without Fear, ed. 2. New York, Harper &

Row Publishers Inc, 1959.

3. Scott JR, Rose NB: Effect of psychoprophylaxis (Lamaze prepara- tion) on labor and delivery in primiparas. N Engl J Med 1976;

294:1205.

Figure 6-3. Placement of TENS electrodes on a patient’s back.

(From DeVore JS, Hughes SC: Psychologic and alternative techniques for obstetric anesthesia, in Shnider SM, Levinson G (eds): Anesthesia for Obstetrics. Baltimore, Williams &

Wilkins, 1987. Used by permission.)

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4. Leboyer F: Birth Without Violence. London, Wildwood House, 1975.

5. Wallis, Shnider SM, Palahniuk RJ, et al: An evaluation of acupunc- ture analgesia in obstetrics. Anesthesiology 1984; 41:596.

6. Bundsen P, Peterson LE, Selstam U: Pain relief in labor by tran- scutaneous electrical nerve stimulation: A prospective matched study. Acta Obstet Gynecol Scand 1981; 60:459.

7. Scanlon RA, Viernstein MC, Long DM: Reduction of postoperative pain and narcotic use by transcutaneous electrical nerve stimula- tion. Surgery 1980; 87:142.

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