7.4 Autonomic Dysreflexia

Question 1

A 26-year-old male is brought in by ambulance to A&E with a history of a fall from the eighth floor.

The neck is immobilised with collar and sandbags.

At what levels are the cervical
spines more vulnerable?

Answer 1

Most cervical spine fractures happen at C2 (one third of the cases)

and C6/C7 (half the cases).

Most fatal injuries occur at C1 or C2.

Question 2

How would the patients with nonfatal injury present?

Answer 2

Symptoms
* Limited range of movement associated with pain
* Weakness, numbness, and paraesthesia along affected nerve roots

Signs
* Loss of diaphragm function in C1/2 injuries

• Spinal shock
  ° Flaccidity
  ° Areflexia
  ° Loss of sphincter tone
  ° Priapism
• Neurogenic shock
  ° Hypotension
  ° Paradoxical bradycardia
  ° Warm and flushed skin
• Autonomic dysfunction
  ° Ileus
  ° Urinary retention

Question 3

How would you manage an acute c3/4 spinal cord injury?

Answer 3

• ATLS approach and ABCDE protocol.
• Stabilise and immobilise the spine.
• Airway and breathing:
  Indications for intubation are acute respiratory failure,
  decreased GCS,
  increased pCo2, and
  decreased tidal volumes.
  In this patient with C3/4 injury, intubation and ventilation are often required.
• Circulation: Treat any associated haemorrhagic shock or spinal shock
  with careful fluid replacement.
• Immediate referral to a neurosurgical centre for further management.

Question 4

This patient suffered a complete C3/4 cord transection and is listed
for debridement of ankle pressure sore 8 months later. He suffers from
significant reflux.

What are your main anaesthetic concerns?

Answer 4

• Risk of aspiration
• Risk of hyperkalaemia with suxamethonium
• Autonomic hyperreflexia
• Choice of anaesthetic: GA or spinal? Any sensation on wound site?
• Difficult airway secondary to tracheostomy and spine fixation
• Latex sensitivity secondary to prolonged use of gloves during urinary
  catheterisation in a neurogenic bladder

Question 5

What is autonomic hyperreflexia?

Answer 5

Autonomic hyperreflexia develops in individuals with a spinal cord injury
above the T6 vertebral level.

It is a medical emergency with complications resulting
from sustained severe peripheral hypertension.

A strong stimulus caused by
bladder distension,
urinary tract infection,
bowel impaction, and
various surgical procedures triggers this condition.

A stimulus below the level of injury causes a
peripheral sympathetic response through the
spinal nerves resulting in vasoconstriction
below the level of injury.

The central nervous system, being not able to detect the stimuli below
the cord due to lack of continuity,

detects only sympathetic response and then sends
inhibitory response down the spinal cord.

This reaches only until the level of injury and
does not cause a desired response in the sympathetic
fibres below the injury, leaving the hypertension unchecked.

Above the level of injury:
Predominant unopposed parasympathetic response
leading to flushing and sweating,
pupillary constriction and nasal congestion,
and bradycardia.

Below the level of injury: Sympathetic overactivity giving a pale, cool skin.

Question 6

Why T6?

Answer 6

The level depicts the autonomic supply to the biggest reservoir of blood,
the splanchnic circulation.

The greater splanchnic nerve arises at T5–9,
and any lesions above T6 allow

the strong uninhibited sympathetic tone to constrict the splanchnic bed,
causing systemic hypertension.

Lesions below T6 results in a
good parasympathetic inhibitory control
prevents hypertension.

Question 7

What is the physiological explanation for this response?

Answer 7

Not fully known. one theory is that the peripheral alpha adrenergic receptors
associated with the blood vessels become hyper-responsive below the
level of spinal cord injury due to the low resting catecholamine levels.

These ‘orphaned’ receptors have a decreased threshold
to react to adrenergic
stimuli with an increased responsiveness.

It has also been postulated that the loss of descending inhibition is
responsible for this mechanism.

Question 8

How would you tailor your anaesthetic for this patient and minimise risk of hyperreflexia?

Answer 8

• Seek senior help
• Use of general or regional anaesthesia +/– sedation

Regional anaesthesia
* Difficult positioning
* Prepare vasopressors

General anaesthesia
* Prepare vasopressors and atropine (excessive hypotension on induction)
* May need RSI because of reflux—avoid suxamethonium (increase in K+!)
* Possible difficult intubation due to positioning
* Adequate anaesthesia and remifentanil to reduce stimulus

others
* Careful temperature control due to altered temperature regulation
* Arterial line in severe cases
* Ensure bladder is not distended

Question 9

What drugs can be given if dysreflexia happens with severe hypertension?

Answer 9

• Short-acting antihypertensives, such as nifedipine or nitrates
• Remifentanil or other short-acting opioids
• Deepening of anaesthesia