Definition of Autonomic Dysreflexia
Autonomic dysreflexia is a life-threatening emergency condition characterized by sudden severe hypertension (systolic blood pressure >150 mmHg and/or 20 mmHg above baseline) occurring primarily in patients with spinal cord injuries at or above the T6 level, accompanied by classic symptoms including flushing, sweating, headache, blurry vision, and a sense of impending doom. 1
Core Pathophysiology
Autonomic dysreflexia results from excessive, uncontrolled activation of the sympathetic nervous system in response to noxious stimuli below the level of spinal cord injury. 2, 3 The condition occurs because:
Spinal cord injury at or above T6 disrupts descending pathways from central control centers to spinal sympathetic neurons, resulting in loss of supraspinal control over sympathetic outflow below the injury level. 4
Noxious stimuli below the injury level trigger unmodulated reflex sympathetic hyperactivity, causing massive vasoconstriction and severe hypertension that cannot be adequately suppressed by higher brain centers. 3, 5
Bradycardia often accompanies the hypertension due to unopposed parasympathetic activity via the intact vagus nerve, which responds to the elevated blood pressure through baroreceptor reflexes. 1, 4
Clinical Presentation
The symptom complex includes: 1, 3
- Sudden severe hypertension (systolic BP >150 mmHg or ≥20 mmHg above baseline)
- Pounding headache
- Profuse sweating above the level of injury
- Flushing of skin above the injury level
- Blurred vision
- Nasal congestion
- Sense of impending doom or anxiety
- Bradycardia (though tachycardia can occur)
- Piloerection ("goosebumps") above the injury level
Epidemiology and Risk Factors
Autonomic dysreflexia occurs in 48-60% of patients with complete spinal cord injuries at or above T6, though it is rare in injuries below this level. 2, 6 The T6 level is critical because it represents the threshold above which sufficient sympathetic outflow is disconnected from supraspinal control to produce the syndrome. 3, 5
Common Triggers
The most frequent precipitating factors include: 2, 6
- Bladder distension (most common trigger)
- Urinary tract infections
- Bowel impaction or distension
- Pressure ulcers (decubitus ulcers)
- Urological procedures or catheterization difficulties
- Spasticity
- Gynecological issues in women
- Any noxious stimulus below the level of injury
Critical Importance
Without timely and effective treatment, autonomic dysreflexia can lead to cerebral hemorrhage, retinal hemorrhage, seizures, heart failure, pulmonary edema, myocardial infarction, or death. 5, 7 The condition represents a medical emergency requiring immediate recognition and intervention. 1, 3
Key Clinical Caveat
Autonomic dysreflexia can be easily missed by medical staff unfamiliar with this condition, particularly when symptoms are attributed to other causes such as sepsis or primary hypertension. 6 Healthcare providers caring for patients with spinal cord injuries at T6 or above must maintain high clinical suspicion for this diagnosis when sudden hypertension and associated symptoms occur. 7