3.3 Autonomic Dysreflexia & Acute Complications

3.3 Autonomic Dysreflexia & Acute Complications

Spinal cord injuries at or above the T6 spinal level interrupt descending central autonomic pathways, leaving sympathetic preganglionic neurons isolated from brainstem inhibitory control. This autonomic disorganization predisposes patients to Autonomic Dysreflexia (AD), a hypertensive emergency that requires immediate recognition and systematic management. In addition to AD, acute medical management of SCI encompasses cardiovascular dysregulation (orthostatic hypotension) and venous thromboembolism (VTE) prevention.

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Autonomic Dysreflexia (AD)

Pathophysiology & Mechanisms

Autonomic Dysreflexia occurs almost exclusively in individuals with SCI at T6 or above, because the major sympathetic splanchnic outflow originates between T5 and L2.

1. Noxious Stimulus: A sensory stimulus below the level of injury (e.g., bladder or bowel distension) sends afferent pain impulses up the spinal cord.
2. Uninhibited Sympathetic Response: The impulses reach the isolated thoracolumbar sympathetic chain, triggering widespread sympathetic vasoconstriction of the splanchnic vascular bed.
3. Severe Hypertension: Massive vasoconstriction causes a rapid, dangerous rise in systemic blood pressure (systolic BP can exceed 200-300 mmHg).
4. Baroreceptor Reflex: Carotid sinus and aortic arch baroreceptors detect the acute surge in BP and send signals via cranial nerves IX and X to the vasomotor center in the medulla.
5. Parasympathetic Activation Above Lesion: The medulla responds by increasing parasympathetic (vagal) output to the heart, inducing reflex bradycardia, and sending descending inhibitory signals down the cord. However, descending inhibition is blocked at the SCI lesion site.
6. Clinical Dichotomy: Vasodilation and sweating occur above the level of injury (flushing, sweating, nasal congestion), while vasoconstriction and piloerection persist below the level of injury (cool, pale skin, goosebumps).

Clinical Presentation & Diagnostic Triad

• Hypertension: Acute elevation of systolic BP >20 to 40 mmHg above baseline. Note that baseline resting BP in tetraplegic patients is normally low (80-100/50-60 mmHg); thus, a BP of 130/80 mmHg may represent severe AD in a high SCI patient.
• Pounding Headache: Severe, sudden onset throbbing frontal or occipital headache.
• Profuse Diaphoresis & Flushing: Sweating and red blotchiness above the NLI level.
• Reflex Bradycardia: Relative or absolute bradycardia (though tachycardia occurs in up to 20% of cases).
• Nasal Congestion & Blurred Vision: Secondary to cranial vasodilators.
• Complications of Untreated AD: Hypertensive encephalopathy, intracranial hemorrhage, retinal detachment, seizures, cardiac arrhythmias, myocardial infarction, and death.

Triggers of Autonomic Dysreflexia

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Stepwise Acute Management Protocol

When a patient at or above T6 develops signs of AD, the physiatrist and nursing staff must immediately execute a mandatory, standardized protocol:

1. Positioning: Immediately sit the patient upright at 90 degrees with lower extremities dangling dependent. This utilizes orthostatic venous pooling to decrease venous return and lower blood pressure.
2. Remove Restraints: Loosen tight clothing, abdominal binders, elastic compression stockings, and leg bag straps.
3. Monitor Vital Signs: Measure BP and HR every 2 to 5 minutes.
4. Check Bladder (#1 Trigger):
   • If an indwelling Foley catheter is present, check for kinks or blockages. Irrigate gently with 15-30 mL of warm sterile saline. If blocked, replace the catheter immediately.
   • If no catheter is present, perform immediate straight catheterization using topical 2% lidocaine jelly as a lubricant (allow 3-5 minutes for local anesthesia to avoid triggering further dysreflexia).
5. Check Bowel (#2 Trigger): If BP remains elevated after addressing the bladder, perform a digital rectal examination (DRE) for fecal impaction. Always instill 2% lidocaine jelly into the rectum and wait 5 minutes prior to digital intervention.
6. Pharmacotherapy: If systolic BP remains elevated (>150 mmHg or >20-40 mmHg above baseline) despite non-pharmacological measures:
   • First-line Agent: Nitroglycerin 2% Ointment (Nitropaste), 1/2 to 1 inch applied topically above the level of injury. Advantage: Can be rapidly wiped off if blood pressure drops precipitous once the offending trigger is removed.
   • Alternative Agents: Immediate-release sublingual nifedipine (10 mg; note: avoid bite-and-swallow capsule forms due to stroke risk), captopril (25 mg sublingual), or intravenous hydralazine in monitored settings.
   • Caution: Never administer nitrates if the patient has taken a phosphodiesterase-5 (PDE-5) inhibitor (e.g., sildenafil, tadalafil) within the past 24-48 hours.

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Orthostatic Hypotension in SCI

Loss of sympathetic vasoconstrictor tone and absence of lower extremity skeletal muscle pump activity produce profound orthostatic hypotension in acute and subacute SCI (especially T6 and above).

• Symptoms: Lightheadedness, dizziness, presyncope, fatigue, blurry vision when elevating head.
• Non-Pharmacological Management: Gradual verticalization using tilt tables, abdominal binders (compresses splanchnic bed), thigh-high compression stockings, and aggressive oral hydration.
• Pharmacological Interventions:
  • Midodrine: Direct alpha-1 adrenergic agonist (5-10 mg TID, taken during daytime hours; avoid before bedtime to prevent supine hypertension).
  • Fludrocortisone: Mineralocorticoid promoting sodium and water retention (0.1 to 0.2 mg daily).
  • Droxidopa: Synthetic amino acid precursor of norepinephrine.

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Venous Thromboembolism (VTE) Prophylaxis

Patients with acute SCI are at extraordinarily high risk for Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE) due to Virchow's triad: stasis (flaccid paralysis), hypercoagulability (acute trauma reaction), and endothelial injury.

• Peak Risk Window: First 2 to 12 weeks post-injury.
• Prophylactic Regimen: Low-Molecular-Weight Heparin (LMWH, e.g., enoxaparin 30 mg SC BID or 40 mg SC daily) combined with mechanical prophylaxis (Sequential Compression Devices [SCDs]).
• Recommended Duration: Minimum of 8 to 12 weeks for motor-complete SCI (AIS A and B) or until discharge from acute rehabilitation.