B11. Obstetrical analgesia and anaesthesia

Page created on December 27, 2021. Last updated on January 17, 2022 at 20:23

Physiology of labour pain

Labour pain has both visceral and somatic components. Visceral pain occurs in both the first and second stages of labour and is due to dilation and ischaemia. Segments T10 – L1 are involved. Somatic pain occurs in the late first stage and second stage and is due to stretching of the vagina, pelvic floor, and ligaments. Segments S2 – S4 are involved.

As such, neuraxial analgesia must block T10 to L1 for the first stage of labour, but if the aim is to give analgesia for the second stage as well, it must also include S2 – S4. However, providing complete analgesia of S2 – S4 prevents the mother from pushing, so the neuraxial block is prepared so that S2 – S4 are not at all or only mindly blocked.

Anaesthesia for vaginal delivery

In most cases, obstetric anaesthesia is neuraxial (as opposed to general). There are multiple reasons for this:

  • It allows for the mother to assist in pushing, and it allows for immediate baby-to-chest
  • It avoids the need for airway instrumentation
  • It reduced the amount of systemic medication and transfer to foetus
  • General anaesthesia may cause early neonatal depression
  • It is known that neuraxial analgesia and anaesthesia has no negative effects on the neonate

A simple request from the mother is sufficient indication for anaesthesia. No specific medical indication is necessary.

Options for anaesthesia for vaginal delivery include spinal, epidural, combined spinal-epidural (CSE), and general anaesthesia. In case of vaginal delivery, epidural is usually preferred. A combination of (diluted) local anaesthetic and (fat-soluble) opioid is administered. The catheter may be left in place to administer postoperative analgesia as well.

Operative vaginal delivery, especially forceps delivery, is more painful than normal delivery. As such, the doses of anaesthetics in case of operative vaginal delivery must be higher. A pudendal nerve block may also be used for anaesthesia in operative vaginal delivery, either alone or as a supplement to neuraxial anaesthesia.

Nitrous oxide (N2O) may be used alone or as a supplement to neuraxial analgesia. It is self-administered by the mother.

Anaesthesia for C-section

Choices for anaesthesia for C-section include spinal, epidural, combined spinal-epidural (CSE), and general anaesthesia. The choice is usually spinal.

Contraindications to neuraxial anaesthesia are rare and relative, and include:

  • Coagulopathy
  • Spinal pathology (infection)
  • Increased ICP

General anaesthesia is indicated in emergencies (when there is no time to achieve neuraxial anaesthesia) or when neuraxial anaesthesia is contraindicated. Inhaled anaesthetics cause uterine relaxation, which may cause uterine atony and haemorrhage. As such, the use of inhaled anaesthetic should be reduced as much as possible. Often, inhaled anaesthetics are used for induction while IV anaesthetics are used for maintenance.

Postoperative analgesia

If neuraxial anaesthesia was used, the catheter may be left in place and be used to administer postoperative analgesia, most commonly low dose morphine.

Paracetamol and NSAIDs are also effective as postoperative analgesia and are usually administered routinely. A single dose dexamethasone may also be administered, as it has analgetic and antiemetic effects.

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