early first stage: pain via visceral afferents enter the spinal cord at T10-L1 dilatation of the cervix lower uterine distensio...
- 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
- 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
- third stage of labour is usually well tolerated with spontaneous placental delivery
- analgesia may be necessary for manual extraction of placenta
Psychoprophylaxis and Physical Analgesia
- “natural childbirth” (e.g. Lamaze prenatal classes) whereby an informed mother utilizes relaxation techniques to stimulate the descending inhibitory pathways
- whirlpool baths, transcutaneous nerve stimulation (TNS), and acupuncture inhibit nociceptive impulses and reduce pain propagating muscle tension
- especially effective in early stages of labour
- 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
- nitrous oxide
- 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
