Management of Pain in Obstetrics 1

By Dr. Chathura Ratnayake

 

What is Obstetric Pain?

Pain related to childbirth may present,

during pregnancy, during labor when more than 95% of women report pain.

during Caesarean section (CS) if there is a poor quality nerve block or prolonged surgery.

after delivery when more than 70% of mothers report acute or chronic pain.

during episiotomy and instrumental deliveries.

     The majority of women report pain during labor but pain intensity is of variable severity.

 

Major determinants of pain intensity are:

Parity -when pain intensity during labor was measured using a unidimensional score (i.e. mild, moderate and severe), 60% of nulliparous and 45% of multiparous women described pain as severe.

Back pain in pregnancy

Antenatal preparation

Upright posture during labor

 

How Does Labor Pain Compare with Other Conditions (in descending order)?

 

Nulliparous women during labor

Labor pain in nulliparous women who had antenatal classes to prepare for labor pain

Labor pain in multiparous women

Chronic back pain

Cancer pain

Toothache

Pain from a fracture

 

Psychosocial Influences on Pain Perception

     Obstetric pain is not only related to the physical process of childbirth but also to psychosocial factors that are operating at the time. Childbirth elicits a wide range of emotions, expectations and experiences, suggesting that psychosocial factors play an important role. For example, one contributing factor to the increase in Caesarean section rates is thought to be mother’s fear of childbirth. Fear and anxiety are significant influences on pain experiences, which is one reason why mother’s are accompanied by a ‘significant’ other person during childbirth.

     In one study in the context of elective Caesarean section showed that mother’s fears were maximal at the time of her nerve block.

     Postnatal pain intensity was predicted by psychosocial factors like, negative expectations, perceived lack of control over analgesics, fear during caesarean section and her partner’s fear.

 

Physiology of Pain in Labor

     Labor pain is the result of many complex interactions, physiological and psychological, excitatory as well as inhibitory.

Pain during the first stage of labor is due to:

distention of the lower uterine segment

mechanical dilatation of the cervix

stretching of excitatory nociceptive afferents resulting from the contraction of the uterine muscles.

The severity of pain increases parallel to the duration and the intensity of contraction.

Pain in the second stage:

      In addition to above factors, traction and pressure on the parietal peritoneum, uterine ligaments, urethra, bladder, rectum, lumbosacral plexus, fascia and muscles of the pelvic floor also contributes to increase the intensity of pain.

Neural pathway of pain

     The uterus and cervix are supplied by afferents accompanying sympathetic nerves in the uterine and cervical plexuses, the inferior, middle and superior hypogastric plexuses and the aortic plexus. The small unmyelinated 'C' visceral fibers transmit nociception through lumbar and lower thoracic sympathetic chains to the posterior nerve roots of the 10th, 11th and 12th thoracic and also to 1st lumbar nerves to synapse in the dorsal horn. The chemical mediators involved are bradykinin, leukotrienes, prostaglandins, serotonin, substance P and lactic acid. As the labor progresses severe pain is referred to the dermatomes supplied by T10 and L1.

     In the second stage, the direct pressure by the presenting part on the lumbosacral plexus causes neuropathic pain. Stretching of the vagina and perineum results in stimulation of the pudendal nerve (S2, 3 and 4) via fine, myelinated, rapidly transmitting 'A delta' fibers. From these areas, the impulses pass to dorsal horn cells and finally to the brain via the spino-thalamic tract.

The stress response to pain in labor

     Segmental and supra-segmental reflex-responses from the pain of labor may affect respiratory, cardiovascular, gastro-intestinal, urinary and neuro-endocrine functions.

Respiratory:

     Pain in labor initiates hyperventilation leading to maternal hypocarbia, respiratory alkalosis and subsequent compensatory metabolic acidosis. The oxygen dissociation curve is shifted to the left and thus reduces tissue oxygen transfer, which is already compromised by the increased oxygen consumption associated with labor.

Cardiovascular:

     Labor results in a progressive increase in maternal cardiac output, primarily due to an increase in stroke volume, and, to a lesser extent, maternal heart rate. The greatest increase in cardiac output occurs immediately after delivery, from the increased venous return associated with the relief of venocaval compression and the auto-transfusion resulting from uterine involution.

Endocrine:

     Pain results in the release of beta-endorphin and adrenocorticotropic hormone (ACTH) from the anterior pituitary. Associated anxiety also induce further pituitary response. Pain also stimulates an increased release of both adrenaline and noradrenaline from the adrenal medulla, which may lead to a progressive rise in peripheral resistance and cardiac output. Excessive sympathetic activity may result in incoordinate uterine action, prolonged labor and abnormal fetal heart-rate patterns. Activation of the autonomic nervous system also delays gastric emptying and reduces intestinal peristalsis.

Metabolic:

     Maternal: During labor, glucagon, growth hormone, renin and antidiuretic hormone (ADH) level increases while insulin and testosterone level decreases. Circulating free fatty acids and lactate also increase with a peak level at the time of delivery.

     Fetal: Maternal catecholamines secreted as a result of labor pain may cause fetal acidosis due to low placental blood flow.

Severity of labor pain

     The severity of labor pain varies greatly among women in labor. If women are asked during or shortly after birth to rate their labor pain, many rate it as severe while a few record a little or no pain. Using the McGill pain questionnaire, Melzack et al. in Montreal, Canada, found that the intensity of labor pain is usually rated high, particularly among primiparae, those with a history of dysmenorrhea, and those belonging to low socio-economic status.

 

Principles of Pain Relief

     The essentials of obstetric pain relief are simplicity, safety and preservation of fetal homeostasis. Women who are given any form of analgesia should be monitored closely.

Techniques available for pain relief in labor

A. Psychological methods of pain relief

     Methods of psychological pain management can be divided into two broad categories, i.e. the Lamaze technique (Natural child birth /Psycho prophylaxis /birth education) and hypnosis.

     Each technique claims the elimination of pain without any harm to the mother, the baby or to the progress of labor and without the need for chemical analgesia. All require adequate antenatal preparation; still, most women experience severe labor pain. Psychological analgesia can place increased demand on the staff.

· Childbirth education and support during labor (Lamaze method)

              It involves following birth practices :

· Let labor begin on its own

              Letting the body go into labor on its own -the baby is ready for birth and the body is          ready for labor.

· Walk, move around and change positions throughout labor

              Moving in labor (not confined to a bed) - helps women cope with strong and painful          contractions, while gently moving the baby into the pelvis and through the birth canal.

· Bring a loved one, friend or doula for continuous support

              In childbirth, a woman is said to feel better when supported by people she trusts and        those who use encouragement.

· Avoid interventions that are not medically necessary

              As the basis is natural birth process, the use of medical interventions is considered to be        negative.

· Avoid giving birth on back and follow the body's urges to push

              Upright positions are safe during pushing and can make it easier to push the baby out.        This could mean squatting, sitting or lying on the side.

· Keep mother and baby together - it's best for mother, baby and breastfeeding

              Mother and baby share a natural instinct to be close after birth. A healthy newborn need        to be placed and cared for skin-to-skin on the mother's abdomen or chest.

 

B. Hypnosis

     Hypnosis can produce analgesia and amnesia during labor and delivery for some selected patients. Only about 25% of women however, are suitable as deep trance hypnotic subjects. And the technique relies on extensive preparation.

 

C. Bio-feedback

     This is a borderline technique between psychological and physical methods of analgesia. Relaxation is a major component of psychological preparation of child-birth and is claimed to relieve pain, reduce anxiety and speed up labor.

 

Physical Methods of Pain Relief

     There are three common techniques: Transcutaneous Electrical Nerve Stimulation (TENS), acupuncture and water (bath or shower).

 

A. TENS (Transcutaneous electrical nerve stimulation)

     TENS was introduced to relieve pain in childbirth in the early 1980s. Since then the use of TENS in labor has become increasingly popular as it is simple to use and is non-invasive. The action of TENS depends on the two principal theories:

 

1.    A-fibers are stimulated by the electrical stimulation preventing the transmission of        afferent noxious stimulus originating from C-fibers,

2.    The electrical stimulus increases endorphins and enkephalins within the system.

 

     TENS electrodes are applied over the dermatomes supplied by T10 to L1. The TENS machine gives a low background stimulus which can be augmented at the time of each contraction. It has been observed in clinical practice that TENS may provide limited pain relief during the first stage of labor. Meta-analysis of randomized controlled trials on the effectiveness of use of TENS in labor does not, however, confirm its efficacy.

B. Acupuncture

     Mentioned in the literature in 581 B. C. and widely practiced in China. Acupuncture is not used for childbirth in China, however, and there is no acupuncture points described for pain relief in labor.

C. Water birth

     A bath or shower is relaxing and should be encouraged. Many maternity units in west have the facility to offer water birth. Its use is mainly during the first stage of labor.  A very few units would encourage the use of the birthing pool for the delivery of the baby. At present there is little evidence to support the use of immersion in water during labor.