Neurogenic Shock

Neurogenic shock is a distributive state caused by sudden loss of sympathetic outflow after injury to the cervical or high thoracic spinal cord (above T6). Unopposed parasympathetic tone causes vasodilation, bradycardia and loss of the cardiac accelerator fibres (T1 to T4). The syndrome complicates 10 to 20% of cervical cord injuries and 3 to 5% of thoracic injuries, and also follows high spinal or epidural anesthesia, severe head injury with brainstem involvement, and Guillain-Barre syndrome with dysautonomia.

The classic triad is hypotension, bradycardia and hypothermia (poikilothermia). Onset is within minutes of injury, and the state lasts days to weeks (typically 1 to 3 weeks). Spinal shock is a different concept: temporary loss of reflexes and flaccid paralysis below the lesion, which resolves over days to weeks (the bulbocavernosus reflex returning ends it). Both can coexist.

Neurogenic shock carries a risk of cord hypoperfusion, which worsens neurological outcome. Complications: cardiac arrest from bradycardia (especially during suctioning), arrhythmia, hypothermia, pulmonary edema from excess fluid, venous thromboembolism, pressure injury, and later orthostatic hypotension and autonomic dysreflexia.

• Hypotension (systolic pressure under 90 mmHg) with warm, dry, pink skin and normal or slow pulse
• Bradycardia (under 60 beats a minute) with a narrow or normal pulse pressure
• Hypothermia, priapism, diaphragmatic breathing, and flaccid paralysis with sensory level
• Absent cremasteric and deep tendon reflexes in spinal shock
• Hypotension that is more severe with head-up positioning
• Red flags: heart rate under 40 beats a minute, asystolic episodes, respiratory failure with high cervical injury, and associated chest or abdominal bleeding

1. Trauma assessment first: hypotension in a trauma patient is hemorrhage until proven otherwise. Search for bleeding with ultrasound (extended examination), chest and pelvis films, and CT. A tachycardic, cold patient is not neurogenic.
2. Neurological examination: motor and sensory level, rectal tone, reflexes and priapism.
3. Spinal imaging: CT of the whole spine, and MRI to define cord injury, hematoma and compression.
4. ECG and continuous monitoring, temperature, arterial blood gas and lactate.
5. Electrolytes and creatinine, and urine output through a catheter.

Differentials: hemorrhagic shock, cardiogenic shock (contusion), tension pneumothorax, tamponade, septic shock and adrenal crisis.

1. Airway and spinal protection: manual in-line immobilization, intubation with care for high cervical lesions (atropine ready, since laryngoscopy can cause bradycardia and arrest). Avoid succinylcholine after the first 48 hours.
2. Fluids: IV balanced crystalloid 500 mL boluses to reach euvolemia, with caution since over-resuscitation causes pulmonary edema in a vasodilated patient (children 10 to 20 mL/kg boluses).
3. Blood pressure target: mean arterial pressure 85 to 90 mmHg for 5 to 7 days after spinal cord injury, to protect cord perfusion, using an arterial line.
4. Vasopressors: norepinephrine 0.05 to 0.5 micrograms/kg/min IV (first-line), or phenylephrine 0.5 to 3 micrograms/kg/min IV if heart rate is high enough. Dopamine 5 to 20 micrograms/kg/min IV helps bradycardia and hypotension.
5. Bradycardia: atropine 0.5 to 1 mg IV every 3 to 5 minutes up to 3 mg (children 0.02 mg/kg, minimum 0.1 mg). Refractory cases: aminophylline 5 mg/kg IV over 30 minutes then 0.5 mg/kg/h, or theophylline orally, glycopyrrolate 0.2 mg IV, and transcutaneous or transvenous pacing.
6. Hypothermia: warm blankets, warmed fluids and warm room.
7. Methylprednisolone is not recommended.
8. Prevention of complications:
   • Enoxaparin 40 mg SC daily from 24 to 72 hours after bleeding is controlled.
   • Pressure care every 2 hours, bladder catheter, bowel program, stress ulcer prophylaxis with omeprazole 40 mg IV daily.
   • Early specialist spinal surgery and rehabilitation.
9. Chronic orthostatic hypotension: abdominal binder, compression stockings, salt 6 to 10 g daily, midodrine 5 to 10 mg orally three times a day (last dose 4 hours before bedtime, avoid supine hypertension) and fludrocortisone 0.1 to 0.2 mg orally daily.
10. Autonomic dysreflexia (later, with lesions above T6): sit the patient up, loosen clothes, relieve the trigger (bladder, bowel), and give nifedipine 10 mg orally (bite and swallow) or glyceryl trinitrate 0.4 mg sublingually for blood pressure over 150 mmHg.

Follow-up in a spinal injury unit. Counsel the patient and family on autonomic complications and warning signs.