FRCA Notes

Analgesia for Labour

In addition to requiring knowledge of the "methods of analgesia during labour", the intermediate curriculum asks for sensitivity regarding "patient choices in obstetric practice – even when this is not in line with accepted evidence based best practice".

Resources

First stage (visceral pain)

  • Pain arises due to:
    • Muscle tension in the lower uterine body and fundus during contraction
    • Cervical dilatation

  • Visceral C-fibre afferents travel with sympathetic nerves
  • Travel via uterine and cervical plexuses
  • Transmit pain centrally via T10 - L1 nerve roots

  • May respond to opioids

Second stage (somatic pain)

  • Pain arises due to perineal, pelvic floor and vaginal stretching/injury

  • Somatic Aδ fibre afferents travel via the pudendal nerves
  • Transmit pain centrally via S2 - S4 nerve roots and via ilio-inguinal and genitofemoral nerves (L1/2)

  • Tends to be refractory to opioids

  • TENS machine
  • Hypnotherapy
  • Acupuncture
  • Aromatherapy
  • Birthing pool
  • Massage
  • Music (inc. whale sounds...)

  • Although paracetamol is a viable analgesic it is unlikely to cut the mustard as a sole agent
  • Entonox is widely used owing to its ease, rapidity and efficacy

Systemic opioids

  • IM pethidine at 1mg/kg (max dose 150mg)
    • Can be associated with confusion, sedation and loss of control
    • Norpethidine is an active, pro-convulsant metabolite
    • It accumulates in the foetus as it is a weak base and more ionised in foetal circulation, with peak foetal concentration 2 - 3hrs post-dose
    • Delays maternal gastric emptying

  • IM diamorphine 7.5mg
    • Associated with slightly lower VAS scores at 60mins and 180mins vs. pethidine (IDvIP trial)
    • Longer duration from first dose to delivery (81mins longer)
    • Less neonatal sedation at 2hrs, but no difference in Apgar or need for neonatal resuscitation

  • Remifentanil PCA

Lumbar epidural analgesia

  • Remains the gold standard for labour analgesia
  • Use of low-concentration, high-volume local anaesthetic + opioid is now commonplace e.g. 0.1% bupivacaine + 2μg/ml fentanyl
  • They provide good sensory block without profound motor block

  • Evidence demonstrates they:
    • Do not increase risk of LSCS
    • Do not increase duration of the first stage of labour
    • May increase the rate of instrumental vaginal delivery due to poor expulsive effort or less foetal rotation

  • Modes of delivery include:
    • Continuous infusion: stable analgesia with minimal CV impact, low LA toxicity risk and reduced staff intervention. Total LA volumes are greater, as is motor block
    • Intermittent bolus: reduces total LA volume but increases staff workload and may lead to intermittent regression of analgesia
    • PCEA: reduced total LA volumes and low staff intervention but good analgesia which the patient can escalate in the second stage

Combined spinal-epidural technique

  • Uses a low dose intrathecal dose ± opioid, followed by a low-dose epidural
  • Advantages over standard epidural include:
    • Faster onset
    • Higher quality analgesia and therefore patient satisfaction
    • Reliable sacral block
  • Is not associated with increased hypotension or motor block compared to standard low-dose epidural analgesia

Labour spinal

  • Can be used as the sole analgesic or as a temporising measure to gain control of significant pain to facilitate other analgesia, namely an epidural
  • E.g. 1ml 0.25% (levo)bupivacaine ± 10-20μg fentanyl

Other

  • Lumbar sympathetic block would technically produce analgesia for the first stage of labour by blocking the T11 - L1 sympathetic afferents responsible for transmitting visceral uterine pain
  • Intrathecal catheters are described but require appropriate anaesthetic and midwifery skillsets and familiarity to manage safely