Neurogenic Shock

Definition/Etiology:

• Shock is circulatory collapse, and inadequate tissue perfusion/oxygenation.
• Neurogenic shock is a diagnosis of exclusion in trauma, and hypovolemic shock should be considered and ruled out first.
• 8,000-10,000 traumatic spinal cord injuries occur each year in the United States.
• 19% of cervical spine injuries result in neurogenic shock.
• 7% of thoracic spine injuries result in neurogenic shock.
• Neurogenic shock occurs in 25-50% of brain/spinal cord injury patients, and usually in the first 5 weeks after injury.  
• In neurogenic shock, sympathetic input is lost, and parasympathetic input is unopposed.
• Vasodilation occurs, and a distributive shock results due to pooling of blood in the periphery.
• The body is unable to compensate for the hypotension by increasing heart rate because sympathetic response is disrupted, This results in uncompensated hypotension with bradycardia.
• Sympathetic control is from T1-L2 (fight or flight)
• Parasympathetic control is from mostly cranial nerves and a little bit from S4 (rest and digest)
• When cervical or thoracic injury occurs, only the sympathetic system is interrupted

Pathophysiology:

Spinal cord injury or brain injury produces neurogenic shock:

• Vertebral fracture
• T6 or above
• Dislocation of vertebra
• Torn vertebral ligament
• Disruption or herniation of intravertebral disc
• Loss of sympathetic nervous system input

Clinical Presentation:

Vasodilation:

• Hypotension
• Warm, flushed skin
• Priapism
• Good urine output

Unable to compensate for hypotension:

• Normal heart rate or bradycardia
• Altered mental status

Euvolemic:

• Normal skin turgor
• Moist mucous membranes
• No edema
• No jugular venous distention

Neuro deficits distal to injury:

• Loss of motor
• Loss of sensation
• Loss of reflexes

Collaborative Management:

Labs: CBC, CMP, lactate, ABG, coags, type and cross

Imaging: 

• FAST exam to rule out concomitant hypovolemic shock
• MRI or CT spine/brain

• Vasopressors to keep MAP 85-90 mmHg to minimize secondary spinal injury from hypotension.  Norepinephrine is the preferred vasopressor.  If profoundly bradycardic, Dopamine or Atropine may be of benefit.
• Monitor fluid status and avoid excess IV fluids because edema in the injured spinal column worsens the injury.
• Get a good history.  If on beta blockers, calcium channel blockers, or digoxin, then they could be clouding the picture by suppressing compensatory tachycardia.

Evaluation | Patient Monitoring | Education:

• Continuous cardiac and SaO2 monitoring
• Central venous catheter if vasopressors are needed
• Frequent NIBP vs arterial line
• Foley catheter to monitor urine output
• Neuro ICU admission

Linchpins: (Key Points)

• Early identification/treatment can prevent secondary injury.
• Rule out hypovolemic shock first.
• Neurogenic shock is a diagnosis of exclusion.
• Suspect neurogenic shock with T6 injury or above.