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 capacity
- 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
Horner's 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
- Diaz, A. Cardiovascular Response to Central Neuraxial Blockade. Primary SAQs.
- ANZCA July/August 2007