Neuraxial Blockade

Describe the physiological consequences of a central neuraxial block

Central neuraxial blockade refers to blockade of fibres in the spinal cord by administration of intrathecal or epidural local anaesthetic.

Respiratory Responses

An increasing level of block will lead to greater effects:

  • Thoracic
    • Impediment to active expiration and expectoration due to blockade of intercostals and abdominal wall musculature
    • Loss of vital capcity
    • Loss of some accessory muscle use
  • Cervical
    Impediment due to diaphragmatic blockade.

Cardiovascular Responses

Occur due to blockade of sympathetic chain fibres in the thoracolumbar region.

An increasing level of block will lead to greater effects:

  • Sacral
    Parasympathetic blockade only. Minimal CVS effects.
  • Lower thoracic/lumbar
    Arteriolar and venous vasodilation in lower abdomen and lower limbs, causing a fall in SVR, BP, and GFR.
  • Upper thoracic
    Loss of cardioaccelerator fibres above T5, causing a reduction in heart rate and contractility, compounding hypotension due to fall in SVR.
  • Cranial Nerves
    Vagal blockade will reduce PNS tone and attenuate some of the loss of SNS tone.
  • Brainstem
    Inhibition of vasomotor centre with profound fall in CVS parameters.

CNS Responses

An increasing level of block will lead to greater effects:

  • Cervical
    Horners syndrome (miosis, anhydrosis, ptosis) due to loss of sympathetic trunks.
  • Cranial nerve Pupillary dilation due to CN III blockade.
  • Brainstem and Cerebral Cortex Anaesthesia due to blockade of the reticular activating system and thalamus.

References

  1. Diaz, A. Cardiovascular Response to Central Neuraxial Blockade. Primary SAQs.
  2. ANZCA July/August 2007
Last updated 2017-10-08

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