Residency · Residency · Physical Medicine Rehabilitation
Autonomic Dysreflexia: Recognition and Emergency Management
Overview
Life-threatening medical emergency in spinal cord injury. Occurs in injuries at T6 and above (can rarely occur up to T10). Massive sympathetic discharge below the level of injury triggered by noxious stimuli. Incidence: 48-90% of patients with injuries at or above T6.
Can occur acutely (as early as spinal shock resolution) or chronically. Mortality risk from intracranial hemorrhage, seizures, cardiac arrhythmia if untreated.
Pathophysiology
Noxious stimulus below the injury level triggers afferent signals to spinal cord. Sympathetic outflow activates below the lesion (splanchnic bed vasoconstriction, T6-L2). Profound hypertension results from widespread vasoconstriction below injury level. Baroreceptors in carotid sinus and aortic arch detect hypertension.
Brain attempts compensatory parasympathetic response via vagus nerve (CN X). Bradycardia (not always present). Vasodilation ABOVE the level of injury only. Descending inhibitory sympathetic signals CANNOT pass through the injured cord. Net result: sustained, uncontrolled hypertension below injury + compensatory vasodilation above.
<image>Pathophysiology of autonomic dysreflexia showing sympathetic and parasympathetic pathways above and below the spinal cord lesion</image>
Clinical Presentation
Cardinal Signs
Severe hypertension (systolic BP may rise 20-40 mmHg above baseline). Note: baseline BP in chronic SCI is often 90-110 mmHg systolic. A BP of 150/100 may represent a crisis in SCI. Pounding headache (most common symptom).
Profuse sweating above the level of injury. Flushing above the level of injury. Piloerection (goosebumps) above the level of injury. Nasal congestion.
Below the Injury Level
Pale, cool skin (vasoconstriction). Piloerection below injury.
Cardiac
Bradycardia (classic but not universal - tachycardia can occur). Cardiac arrhythmias. Atrial fibrillation.
Severe Complications if Untreated
Intracranial hemorrhage (subarachnoid, intracerebral). Retinal hemorrhage. Seizures. Pulmonary edema. Myocardial infarction. Death.
Common Triggers (Noxious Stimuli)
Genitourinary (Most Common - 75-85%)
Bladder distension (blocked catheter, kinked tubing, full leg bag). Urinary tract infection. Bladder stones. Urodynamic testing. Cystoscopy. Catheterization itself.
Gastrointestinal (Second Most Common)
Fecal impaction / bowel distension. Digital rectal stimulation during bowel program. Hemorrhoids. Appendicitis, cholecystitis (any acute abdomen). Gastric ulcer.
Integumentary
Pressure injuries. Ingrown toenails. Burns (including sunburn). Tight clothing, restrictive garments. Contact with hard or sharp objects.
Reproductive/Sexual
Sexual activity, ejaculation. Pregnancy, labor, and delivery. Menstruation (less common). Epididymitis.
Other
Deep vein thrombosis. Fractures below injury level. Heterotopic ossification. Surgical procedures without adequate anesthesia.
<image>Common triggers of autonomic dysreflexia organized by organ system with frequency data</image>
Emergency Management Algorithm
Step 1: Sit the Patient Upright
Immediately sit patient up and lower legs (orthostatic effect reduces BP). Loosen any tight clothing, abdominal binders, compression stockings. Monitor BP every 2-5 minutes.
Step 2: Identify and Remove the Cause
Check the bladder FIRST (most common trigger): If catheter in place: check for kinks, blockage, full drainage bag. Flush or replace catheter if obstructed. If no catheter: catheterize immediately using lidocaine jelly.
Check the bowel: If bladder cause eliminated, perform digital rectal exam. Use lidocaine gel 2% before rectal examination (to avoid worsening AD). Remove fecal impaction if present.
If AD worsens during bowel check, STOP and treat pharmacologically first. Check skin: pressure injury, ingrown toenail, tight clothing.
Step 3: Pharmacologic Management
If BP remains > 150 mmHg systolic (or > 20 mmHg above baseline) after removing cause: Nitroglycerine paste 2%: 1-2 inches applied above injury level. Easy to remove if BP drops excessively. CONTRAINDICATED if patient has taken PDE5 inhibitors (sildenafil) within 24-48 hours.
Nifedipine immediate-release: 10 mg bite-and-swallow (not sublingual). Rapid onset (10-15 minutes). Risk of precipitous hypotension. Captopril: 25 mg sublingual. Hydralazine: 10-20 mg IV. Labetalol: 10-20 mg IV (avoid in bradycardia). Clonidine: 0.1-0.2 mg PO.
Step 4: If Refractory
Consider continuous IV infusion: nitroprusside or nicardipine drip. Transfer to ICU for monitoring. Continue searching for and treating the precipitating cause.
<image>Step-by-step emergency management algorithm for autonomic dysreflexia</image>
Prevention Strategies
Education of patient, family, and ALL caregivers (including non-rehabilitation staff). Medical alert identification. Reliable bladder management program (regular CIC schedule, catheter care). Regular bowel program to prevent impaction.
Skin checks and pressure relief. Pre-procedure prophylaxis (before urodynamics, cystoscopy, bowel procedures): Nifedipine 10 mg PO 30 minutes before procedure. Lidocaine gel for urethral/rectal procedures. Carry emergency AD management card/kit.
Special Situations
Autonomic Dysreflexia During Pregnancy and Labor
AD common during labor in women with SCI at T6 and above. Can be mistaken for pre-eclampsia. Epidural anesthesia is both treatment and prevention. Close BP monitoring throughout labor and delivery.
Silent Autonomic Dysreflexia
Elevated BP without classic symptoms. More common in chronic SCI patients who have adapted. May present with only malaise or headache. Importance of routine BP monitoring during procedures.
Autonomic Dysreflexia in Athletes ("Boosting")
Some wheelchair athletes intentionally trigger AD to enhance performance. Inducing bladder distension, tight leg straps, sitting on sharp objects. Banned by International Paralympic Committee. Dangerous practice with risk of stroke and death.
Blood Pressure Considerations in SCI
Baseline BP is often low in chronic cervical and high thoracic SCI (80-100/50-70 mmHg). Standard hypertension thresholds do not apply. A "normal" BP of 120/80 may represent relative hypertension. Document individual baseline BP for each patient.
Clinical Pearls
Always check the bladder FIRST - it is the cause in 75-85% of AD episodes. A systolic BP of 150 mmHg in a patient with chronic SCI whose baseline is 90 mmHg is a hypertensive crisis - do not be falsely reassured by "normal" values. Sitting the patient upright is the fastest initial intervention to lower BP through orthostatic effects.
Apply lidocaine jelly before catheterization or digital rectal exam during an AD episode to avoid worsening the stimulus. Nitroglycerin paste is preferred first-line pharmacotherapy because it can be easily wiped off if BP drops too low. All SCI patients at T6 and above should carry an AD emergency card with their baseline BP documented.
<image>Autonomic dysreflexia wallet card template showing baseline BP, common triggers, and emergency steps</image>
References
- Consortium for Spinal Cord Medicine. Acute management of autonomic dysreflexia: individuals with SCI presenting to health-care facilities. Clinical Practice Guideline. 2nd ed. 2001.
- Krassioukov A, et al. A systematic review of the management of autonomic dysreflexia after spinal cord injury. Arch Phys Med Rehabil. 2009;90(4):682-695.
- Wan D, Krassioukov AV. Life-threatening outcomes associated with autonomic dysreflexia: a clinical review. J Spinal Cord Med. 2014;37(1):2-10.
- Eldahan KC, Bhimani AD, et al. Autonomic dysreflexia after spinal cord injury. Auton Neurosci. 2018;209:59-70.
- Cifu DX, et al. Braddom's Physical Medicine and Rehabilitation. 6th ed. Elsevier; 2020.
