Autonomic hyperreflexia

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Summary

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Autonomic Dysreflexia (AD)

  • Definition: A condition associated with spinal cord injury (SCI) typically at T6 or above.
  • Risk Factors: Higher level SCI and complete lesions.
  • Most commonly presents between 3-6 months after injury
  • Frequency variable: 20-70% of patients
  • Above lesion: reflex bradycardia & vasodilation (flushed)
  • Below lesion: unopposed sympathetic stimulation (vasoconstriction/hypertension)

Mechanism

  1. Noxious stimuli activate pain fibers, sending an afferent impulse to the spinal cord.
  2. This triggers a generalized sympathetic response.
  3. Resulting in an increase in blood pressure.
  • Above the level of injury:
    • Carotid baroreceptors sense the increased blood pressure.
    • Vagus nerve-mediated parasympathetic response increases.
    • Dysregulated parasympathetic response occurs only above the SCI.
  • Below the level of injury:
    • SCI blocks descending inhibitory signals to preganglionic sympathetic neurons.
    • Leads to an increased sympathetic response.
    • Causes splanchnic vasoconstriction.

Clinical Manifestations

  • Bradycardia
  • Sweating
  • Bilateral headache
  • Flushing
  • Nasal congestion
  • Splanchnic vasoconstriction
  • Pallor
  • Piloerection
  • Cold extremities

Consequences

  • Arrhythmia
  • Intracranial pressure increases
  • Pulmonary edema
  • Renal insufficiency
  • Seizures
  • Stroke
  • Death

Note

  • The unregulated sympathetic tone leads to sustained increasing blood pressure.
  • Autonomic dysreflexia occurs with lesions at or above T6 because of the loss of sympathetic control of splanchnic circulation, resulting in a critical mass of blood vessels causing elevated blood pressure.

Considerations

  • Potential for hypertensive emergency with end-organ damage
  • Considerations of chronic SCI
  • Need for invasive monitoring
  • Difficult to assess success of neuraxial technique

Management

  • Discussion with surgeon regarding plan for procedure
  • Remove potential triggers: full bladder, Foley insertion, full rectum, surgical stimulus
  • General anesthetic vs neuraxial technique (if GA, consider a deep anesthetic)

Management of Hypertensive Event

  • Consider deepening level of anesthesia if under GA
  • If epidural, consider top-up

Treat Severe Hypertension with Fast-acting Titratable Agents

  • Nitroprusside 0.5-3 mcg/kg/min or nitroglycerin 5-200 mcg/min
  • Hydralazine 10-20 mg IV prn
  • Phentolamine 5 mg IV prn
  • Look for evidence of end-organ involvement & treat accordingly

Pregnancy Considerations

  • Multidisciplinary discussion regarding plan for labor & delivery
  • Consider scheduled elective cesarean section

If Vaginal Delivery

  • Admit early to monitored bed with telemetry
  • Need continuous BP monitoring with arterial line
  • Remove all preventable triggers of autonomic hyperreflexia (vaginal exams, full bladder = Foley insertion)
  • Start early epidural to prevent hypertensive episodes from contractions

Difficult to Assess Success of Epidural

  • May need larger test dose to rule out subarachnoid placement

Two Ways to Assess Level of Epidural

  1. Sensory block cephalad to level of spinal cord lesion
  2. Evaluating segmental reflexes below level of the lesion: lightly stroke each side of the abdomen above & below the umbilicus, looking for contraction of the abdominal muscles & deviation of the umbilicus toward the stimulus (reflexes are absent below the level of the block)

If Cesarean Delivery

  • Either general anesthetic or neuraxial technique:
    • Must have arterial line
    • Vasodilators drawn up & ready
    • Succinylcholine contraindicated
    • Severe respiratory insufficiency or technical difficulties with neuraxial anesthesia may necessitate the use of general anesthesia

Links

References:

  1. The Calgary Guide to Understanding Disease. (2024). Retrieved June 5, 2024, from https://calgaryguide.ucalgary.ca/
  2. Krassioukov, A. V., Warburton, D. E. R., Teasell, R., & Eng, J. J. (2009). A systematic review of the management of autonomic dysreflexia after spinal cord injury. Archives of Physical Medicine and Rehabilitation, 90(4), 682-695. https://doi.org/10.1016/j.apmr.2008.10.017
  3. Anesthesia Considerations. (2024). Retrieved June 5, 2024, from https://www.anesthesiaconsiderations.com/

Summaries:

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© 2025 Francois Uys. All Rights Reserved.

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