Autonomic Dysreflexia

Potentially life-threatening sympathetic overactivity occurring following noxious stimulation in patients with a spinal injury above T6, characterised by:

• Hypertension
• Bradycardia
• Sensory over-activity below the lesion

Epidemiology and Risk Factors

Pathophysiology

Dysregulated sympathetic action that occurs with both:

• Spinal injury level at T6 or higher
• Noxious stimulus below the spinal level:
  • Ascending sensory fibres convey message to spinal cord
  • Widespread SNS reflex activity occurring below the level of injury
    Sympathetic ganglion activity remains uncontrolled due to lack of descending inhibition.
  • Compensatory parasympathetic activity above the level of injury
    • ↑ BP detected by baroreceptors
      Leads to compensatory bradycardia.

Aetiology

Common causes include:

• Bladder
  • Distension
  • Hyperactivity
  • UTI
  • Stones
  • IDC placement
  • Trans-urethral urological procedures
• Bowel
  • Distension
    • Constipation
    • Gas
  • Rectal irritation
    • Haemorrhoids
• Skin
  • Burns
  • Pressure areas
  • Tight clothing
• GU
  • Intercourse
  • Menstrual cramping
  • Labour
• Pain
  • Lower limb trauma

Clinical Manifestations

Presentation due to SNS overactivity, with compensatory PNS responses:

• B
  • Dyspnoea
• C
  • HTN
    ↑ SBP ⩾20%,
  • Bradycardia
  • Flushing
    Above level.
• D
  • Blurred vision
  • Headache
    Due to HTN.
  • Anxiety/irritation
• E
  • Above level
    • Sweating
      
  • Below level
    • Pallor
    • Piloerection

Diagnostic Approach and DDx

Investigations

Management

• Identify and remove obvious causes
• Control HTN

Blood pressure may drop precipitously following removal of stimulus.

Resuscitation:

Ask the patient/carer for any previous precipitants. Common causes include:

• Limb constriction
  • Loosen constrictive clothing
• Urinary retention
  • Check bladder drainage equipment
    • Kinks
    • Clogging
    • Overfull bag
    • Consider irrigating catheter if blocked
      
  • Consider IDC
• Constipation
  • Consider faecal evacuation
    If bladder empty.

• C
  • Haemodynamic control
    Escalation of therapy:
    • Sit up
    • Remove obvious causes
    • Pharmacological therapy:
      • If SBP >150mmHg
      • Use short acting agents
        Minimises hypotension once stimulus has resolved.
        • GTN 400μg SL
        • Captopril 25mg SL
        • Hydralazine 5mg IV Q10min
        • Labetaolol 5mg IV Q5min
      • Analgesia
        If a noxious stimulus present, e.g. trauma.

Specific therapy:

• Pharmacological
• Procedural
• Physical

Supportive care:

Disposition:

Preventative:

Anaesthetic Considerations

• D
  • Anaesthetic technique
    • General
      Appropriate if there is a risk of autonomic dysreflexia, or muscle spasms.
    • Neuraxial
      Appropriate if there is a risk of autonomic dysreflexia, or muscle spasms.
      • Spinal anaesthesia effectively prevents autonomic dysreflexia
      • Epidural anaesthesia is less reliable, as a patch block may occur
    • Regional/local
      Appropriate if:
      • Reduced sensation at site
      • No risk of autonimic dysreflexia
    • Monitored anaesthetic care
      Appropriate if:
      • No sensation at site
      • No risk of autonomic dysreflexia

Complications

• Death
• CVS
  ~22%.
  • Myocardial ischaemia
  • APO
• CNS
  ~70%; major cause of death.
  • CVA

Prognosis

Key Studies

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References

1. Middleton J, Ramakrishnan K, Cameron I. Treatment of Autonomic Dysreflexia for Adults & Adolescents with Spinal Cord Injuries. Agency for Clinical Innovation. 2013.