Neurogenic Shock

Aka: Neurogenic Shock, Vasogenic Shock

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II. Definitions

  1. Neurogenic Shock
    1. Distributive Shock from neurogenic vasodilation mediated by loss of sympathetic tone
    2. Follows cerebral or Spinal Cord Injury (above T6) affecting sympathtic nervous system
  2. Spinal Shock
    1. In contrast to Neurogenic Shock, Spinal Shock is not a true shock syndrome
    2. Results in Flaccid Paralysis and Deep Tendon Reflex loss below level of Spinal Cord Injury

III. Pathophysiology

  1. Neurogenic Shock results from Severe Head Injury or upper spine injury (above T6)
  2. Peripheral Sympathetic Nerve denervation results in ungoverned Parasympathetic Nerve activity
    1. Loss of vasomotor tone (vasodilation) leading to Distributive Shock
    2. Loss of cardiac Sympathetic Nerve activity, leads to paradoxical Bradycardia

IV. Causes

  1. Severe Head Trauma
  2. Cervical Spine Injury
  3. Thoracic Spine Injury (above T6)

V. Signs

  1. Mnemonic: 70/70 = SBP 70, HR 70
    1. Lack of normal sympathetic tone
  2. Hypotension
    1. Secondary to Bradycardia and vasodilation
    2. Narrow Pulse Pressure is absent
      1. Lack of typical sympathetic response (increased SVR and diastolic BP)
  3. Paradoxical Bradycardia
    1. Expected response is a reflex Tachycardia (a sympathetic response)
  4. Decreased vascular tone (vasodilation)
    1. Absent diaphoresis
    2. Warm extremities
      1. Due to inability to Vasoconstrict and shunt blood back to the core, with risk of Hypothermia

VI. Associated Conditions

  1. See Severe Head Trauma
  2. See Spinal Cord Syndrome
  3. See Cervical Spine Injury
  4. See Thoracolumbar Trauma
  5. Spinal Shock
    1. Flaccid Paralysis and Deep Tendon Reflex loss below level of Spinal Cord Injury
  6. Diaphragm Paralysis
    1. C3-5 Cervical Spine Injury resulting in phrenic nerve denervation

VII. Differential Diagnosis

  1. Hemorrhagic Shock (first priority to manage)
    1. Presents with Tachycardia, Vasoconstriction and cold extremities
    2. In actuality, distinguishing from Neurogenic Shock can be difficult (diagnosis of exclusion)
    3. Hemorrhagic Shock is more common, more immediately deadly and more treatable
      1. Address possible Hemorrhagic Shock with blood replacement first
  2. Other Trauma related shock
    1. Cardiac Injury
    2. Tension Pneumothorax
    3. Pericardial Tamponade

VIII. Pitfalls

  1. Fluid Overload (from aggressive fluid Resuscitation)

IX. Management

  1. Careful Fluid Replacement
  2. Target mean arterial pressure of 85 mmHg or higher (maximizes spinal cord perfusion)
  3. Vasopressors
    1. Norepinephrine is preferred
    2. Avoid alpha-receptor Agonists (e.g. Phenylephrine) due to risk of reflex Bradycardia
  4. Manage Bradycardia (e.g. Atropine, glycopyrrolate)
  5. Consider high dose Corticosteroids (Consult neurosurgery or Spine Surgery)

X. Prognosis

  1. Neurogenic Shock if due to critical Head Injury may indicate terminal event
  2. Prognosis is often poor

XI. References

  1. (2012) ATLS, ACOS, p. 179-80
  2. Rodriguez, Winger, Poulo and Glunk (2023) Crit Dec Emerg Med 37(3): 23-9

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