What is Neurogenic Shock?
Neurogenic shock is a type of shock caused by the sudden cessation of autonomic regulatory signals to the smooth muscle in vessel walls. It is a life-threatening medical emergency.
It is a type of distributive shock that leads to
- Hypotension – decrease in blood pressure
- Bradycardia – Decrease in pulse rate
- Peripheral vasodilatation – dilatation of peripheral blood vessels
This results in the pooling of blood and deficiency of supply to vital organs, leading to shock.
It is very commonly associated with injuries causing damage to the central nervous system damage (brain injury, cervical cord injury or high thoracic cord injury] but could be due to many other reasons as well [see below].
The shock occurs because of the loss of background sympathetic stimulation, which is responsible for maintenance of the tone of blood vessels. As a result of the loss of vascular tone, the vessels suddenly relax resulting in a sudden decrease in peripheral vascular resistance and decreased blood pressure.
Neurogenic shock is also known as vasogenic shock.
It should not be confused with spinal shock [especially in cases of neurogenic chock with spinal injury].
Spinal shock is a different entity and is a reversible cessation of sensory and motor function following spinal cord injury.
[Read more about Spinal Shock]
The joint committee of the American Spinal Injury Association and the International Spinal Cord Society have proposed the following definition
Neurogenic shock is a general autonomic nervous system dysfunction that also includes symptoms such as orthostatic hypotension, autonomic dysreflexia, temperature dysregulation. A focal neurologic deficit is not necessary for the diagnosis of neurogenic shock.
Universal hemodynamic parameters for neurogenic shock have not been defined but most of the studies consider systolic blood pressure less than 100 mmHg and heart rate less than 80 bpm for labeling the condition as the neurogenic shock.
Causes of Neurogenic Shock
Neurogenic shock occurs due to insult/injury to the spinal cord with associated autonomic disturbances. The autonomic dysregulation occurs due to a loss of sympathetic tone that cannot oppose a parasympathetic response.
Traumatic spinal cord injuries are the most common cause, with 19% of cervical spine injuries and 7% of thoracic spine injuries are associated with neurogenic shock. Traumatic brain injuries are associated to a lesser extent.
Other causes of neurogenic shock less common. These include
- Spinal anesthesia
- Administration of autonomic blocking agents.
- Transverse myelitis
- Guillain-Barre syndrome
In children, there is an association of neurogenic shock with Trisomy 21, skeletal dysplasia, and tonsillopharyngitis.
In acute trauma, the cause of shock primarily is the hemorrhagic shock is the more common cause of the decrease in blood pressure. Once that has been managed, and the patient is still not improved, the neurogenic shock should be considered.
Pathophysiology of Neurogenic Shock
The shock results when descending [neural tracts coming from brain to spinal cord] sympathetic tracts are disrupted in the spinal injury.
This occurs both in primary injury, which is direct damage and occurs within seconds, and secondary injury, which is the result of vascular insult, electrolyte imbalance, and edema, and occurs hours to days after the initial insult.]
A loss of sympathetic tone and thus unopposed parasympathetic response driven by the Vagus nerve occurs. The cardiac output decreases because the venule and small veins lose tone. There is a pooling of the blood in the periphery leading to falling of blood pressure.
In the normal situation, a reflex increase in heart rate will occur to compensate for the peripheral pooling of blood. However, in neurogenic shock, blocked sympathetic pathways fail to check bradycardia. Consequently, patients suffer from instability in blood pressure, heart rate, and temperature regulation.
Presentation, Evaluation, and Diagnosis
The surroundings leading to shock are very important in making the diagnosis.
The neurogenic shock could be difficult to diagnose especially in acute traumatic situations. In acute injuries, identification spinal cord trauma is important to consider the diagnosis.
The condition should be considered only after a hemorrhagic shock has been ruled out in a trauma patient.
The features suggesting neurogenic shock are
- Hypotension – Decrease in blood pressure
- Bradycardia – Slow heart rate
- Warm, dry extremities
- Peripheral vasodilation and venous pooling
- Poikilothermia (Cold Body)
- Decreased cardiac output (with cervical or high thoracic injury)
The presence of spinal vertebral fracture or dislocation should raise the concern for neurogenic shock.
Treatment of Neurogenic Shock
Management of neurogenic shock includes hemodynamic stabilization and measures to protect spine further injury in case of acute trauma.
This aims to normal blood pressure and cardiac output.
Low blood pressure or hypotension should be treated as soon as possible so that secondary injury to the cervical spine is prevented. It is done by fluid administration and drugs.
It is recommended to keep the mean arterial pressure at 85–90 mmHg for the first 7 days to improve spinal cord perfusion.
It is the first line of treatment. The fluid administered allows appropriate compensation for the dilatation that vasogenic shock has resulted.
Vasopressors and inotropes
These drugs are second line options given if there is no response to fluid administration
Phenylephrine is the commonly given drug. It is a pure alpha agonist [These bind to ?-receptors on vascular smooth muscle and induce smooth contraction and vasoconstriction] that leads to constriction of the vessels and increases blood pressure
Reflex bradycardia is an undesirable effect because it does not have any beta activity. It adds to the already unopposed vagal tone.
Norepinephrine has both alpha and beta agonist activity. It can control low blood pressure and does not produce reflex bradycardia as well.
In refractory cases, epinephrine is used but rarely needed. Caution should be used when using vasopressors as there may be co-existing injuries exacerbated with vasoconstriction.
Atropine and glycopyrrolate oppose vagal tone and are used for countering severe bradycardia.
Isoproterenol may also be considered for countering bradycardia.
Methylxanthines such as theophylline and aminophylline are used in refractory cases of bradycardia.
Initial c-spine immobilization is important to prevent further spinal cord injury especially in cervical injuries
- Taylor MP, Wrenn P, O’Donnell AD. Presentation of neurogenic shock within the emergency department. Emerg Med J. 2017 Mar;34(3):157-162 [Link]
- Fox AD. Spinal shock. Assessment & treatment of spinal cord injuries & neurogenic shock. JEMS. 2014
- Summers RL, Baker SD, Sterling SA, Porter JM, Jones AE. Characterization of the spectrum of hemodynamic profiles in trauma patients with acute neurogenic shock. J Crit Care. 2013 Aug;28(4):531.e1-5