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PAIN PATHWAYS DURING LABOUR

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  1. early first stage: pain via visceral afferents enter the spinal cord at T10-L1
    • dilatation of the cervix
    • lower uterine distension
    • contraction of the uterus
  2. late first stage and second stage pain via visceral and somatic afferents (pudendal nerve) enter the spinal cord at S1-S5
    • contraction of the uterus
    • distention and stretching of pelvic structures (pelvic peritoneum, fascia, ligaments, and muscles)
    • pressure on lumbar nerves
  3. third stage of labour is usually well tolerated with spontaneous placental delivery
    • analgesia may be necessary for manual extraction of placenta
ANALGESIA

Psychoprophylaxis and Physical Analgesia

  1. “natural childbirth” (e.g. Lamaze prenatal classes) whereby an informed mother utilizes relaxation techniques to stimulate the descending inhibitory pathways
  2. whirlpool baths, transcutaneous nerve stimulation (TNS), and acupuncture inhibit nociceptive impulses and reduce pain propagating muscle tension
  3. especially effective in early stages of labour
Intravenous Analgesia
  1. meperidine (Demerol)
    • best used in early stages of labour, less effective once labour is well established
    • rapidly cleared by fetus if IV (prolonged if IM)
    • peak fetal level 2-4 hours after maternal injection IM
    • can suppress respiration in the newbom (treatment with naloxone)
    • side effects of orthostatic hypotension, nausea, and vomiting
Inhalational Analgesia
  1. nitrous oxide
  2. 50% nitrous oxide in O2
    • self-administered during contractions
    • does not prolong labour or interfere with uterine contractions but administration > 20 minutes may result in neonatal depression
    • provides partial pain relief during labour as well as at delivery
PAIN PATHWAYS DURING LABOUR PAIN PATHWAYS DURING LABOUR Reviewed by Radiology Madeeasy on January 17, 2011 Rating: 5
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