Critical Care Trauma Centre

Question of the Week: July 14, 2000

What is autonomic dysreflexia?


A life-threatening syndrome that can occur in individuals with cord injuries above T6 (most common in quadriplegia).  It is triggered by a noxious stimulus such as full bladder or bowel, and is characterized by hypertension, bradycardia, diaphoresis, and vasodilation above the level of the injury (often recognized by nasal congestion or bounding headache).


Any noxious stimulus can trigger autonomic dysreflexia.  A full bladder or bowel is the most common trigger.  A tight shoelace, pressure sore, painful procedure or any other source of noxious stimulus can also act as a trigger.

The stimulus triggers a sympathetic response.  The release of catecholamines causes vasoconstriction and hypertension.  The hypertension triggers an inhibitory response, which is unable to descend downward below the level of the injury.  Above the level of the lesion, vasodilation and bradycardia are triggered (inhibition).  The vasodilation is often characterized by facial and upper extremity flushing, headache, nasal congestion and diaphoresis.  Below the level of the injury, the vasoconstriction is unopposed, and the hypertension persists.  Untreated, the hypertensive crisis can be life threatening.

Treatment includes removal of the offending stimulus  (e.g. bladder catheterization, bowel elimination) and treatment of hypertension.  If the hypertension is extreme or cannot be quickly relieved, anti-hypertensive agents such as hydralazine or nifedipine.

Meticulous attention to bladder and bowel elimination routines is imperative.  Patients with spinal cord injury (particularly quadriplegics) must be taught to recognize the signs and symptoms of autonomic dysreflexia and know how to instruct others to assist them during crisis.

O'Donnell, W. (1987). Neurological management in patient with acute spinal cord injury. Critical Care Clinics. July. pp 612.

Brenda Morgan
Clinical Educator, CCTC
July 14, 2000

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