Neurogenic Shock 

Definition:
Neurogenic shock is a form of distributive shock caused by loss of sympathetic tone due to disruption of the autonomic pathways within the spinal cord, leading to unopposed parasympathetic (vagal) activity.

It is classically associated with acute spinal cord injury (SCI) at or above the T6 level.


Pathophysiology

Component

Mechanism

Loss of sympathetic tone

Injury to descending sympathetic fibers in the spinal cord → loss of vasomotor tone below lesion

Vasodilation

Arteriolar and venous dilation → ↓ systemic vascular resistance (SVR) and venous return (preload)

Bradycardia

Unopposed vagal (parasympathetic) tone → ↓ heart rate

Hypotension

Due to combined ↓ SVR, ↓ preload, and ↓ cardiac output

Warm, dry skin

Due to vasodilation (unlike cold, clammy skin in hypovolemic shock)

Key distinction:
Neurogenic shock = hemodynamic phenomenon
Spinal shock = loss of reflexes and motor/sensory function below the lesion
(They may coexist, but are distinct entities.)

Feature

Neurogenic Shock

Spinal Shock

Definition

Hemodynamic instability due to loss of sympathetic tone

Temporary loss of spinal cord reflexes below injury

Duration

Hours to weeks

Usually 24–48 hours (up to weeks)

Main feature

Hypotension, bradycardia

Areflexia, flaccid paralysis

Pathophysiology

Autonomic

Neurological

Treatment

Supportive, vasopressors

Time + rehabilitation

Causes

  1. Spinal cord injury (SCI) — most common
    • Cervical or high thoracic (above T6)
    • Due to trauma, fracture-dislocation, penetrating injury, or surgery
  1. Spinal anesthesia or epidural blockade — sympathetic block
  2. Brainstem injury — rarely can mimic neurogenic shock


 Clinical Features

1. Cardiovascular

  • Hypotension: due to loss of sympathetic vasoconstriction
  • Bradycardia: unopposed vagal tone (especially cervical lesions)
  • Warm, flushed, dry skin below lesion

2. Neurological

  • Motor and sensory loss below the level of lesion
  • Loss of reflexes (spinal shock)
  • Priapism (due to unopposed parasympathetic activity)

3. Respiratory

  • Diaphragmatic paralysis (C3–C5 injury)
  • Intercostal muscle weakness → hypoventilation, respiratory failure


Pathophysiological Zones in Spinal Cord Injury

  • Above T1–T4: complete loss of cardiac sympathetic tone → severe bradycardia
  • T1–T4: partial cardiac sympathetic involvement
  • Below T6: usually sparing of cardiac sympathetic fibers → less severe bradycardia


 Diagnosis

Diagnosis is clinical, supported by hemodynamic monitoring and exclusion of other causes of shock.

1. Clinical suspicion

  • Recent spinal cord injury above T6
  • Hypotension + bradycardia + warm extremities

2. Hemodynamic monitoring

  • ↓ SVR, ↓ preload, normal or low cardiac output
  • ↓ filling pressures on PA catheter (CVP/PCWP)

3. Rule out other causes

  • Hypovolemia, hemorrhage, cardiac tamponade, tension pneumothorax


 Management

 1. Airway and Breathing

  • Early airway protection and mechanical ventilation if high cervical lesion or respiratory compromise.
  • Maintain oxygenation and prevent hypercapnia (which increases ICP).


 2. Circulation

  • Goal MAP: ≥ 85–90 mmHg (as per AANS/CNS guidelines for SCI management)
    → Maintained for first 5–7 days post-injury to optimize spinal cord perfusion.

Fluids

  • Use isotonic crystalloids (avoid fluid overload)
  • Carefully differentiate from hemorrhagic shock (may coexist)

Vasopressors

Used if MAP not achieved with fluids:

Agent

Mechanism

Comments

Norepinephrine

α + β agonist

Preferred: increases SVR & CO

Phenylephrine

Pure α agonist

Use if tachycardia present

Dopamine

β + α agonist

Alternative (risk of arrhythmias)

Epinephrine

β > α

In refractory cases

Bradycardia management

  • Atropine (0.5–1 mg IV bolus) for HR < 50/min with symptoms
  • Temporary pacing may be required in refractory cases


 3. Temperature regulation

  • Poikilothermia due to sympathetic dysfunction → use temperature control measures


 4. Spinal cord stabilization

  • Immobilization with cervical collar or spine board
  • Definitive surgical decompression/fixation as early as feasible (within 24 hours ideally)


 5. Pharmacologic adjuncts

  • Corticosteroids:
    • Methylprednisolone high-dose regimens (NASCIS trials) are no longer routinely recommended (per AANS/CNS and SCCM guidelines) due to lack of proven benefit and increased infection risk.
  • VTE prophylaxis: LMWH (unless contraindicated)
  • Stress ulcer prophylaxis: PPIs or H2 blockers


 Prognosis

  • Depends on:
    • Level and completeness of cord injury
    • Timeliness of hemodynamic stabilization
    • Associated trauma (e.g., hemorrhage)
  • Early aggressive hemodynamic support improves neurologic recovery.

Complications

  • Persistent hypotension
  • Cardiac arrest from vagal episodes
  • Autonomic dysreflexia (later phase)
  • DVT / PE
  • Pressure sores


 Autonomic Dysreflexia (Late Complication)

Occurs in chronic SCI above T6.

Trigger:

  • Bladder distension
  • Fecal impaction

Presentation:

  • Severe hypertension
  • Bradycardia
  • Headache
  • Sweating above lesion

Emergency treatment:

  • Sit upright
  • Remove trigger
  • Short-acting antihypertensives (nitrates)



References

  1. Harrison’s Principles of Internal Medicine, 21st ed.
  2. Miller’s Anesthesia, 10th ed.
  3. AANS/CNS Guidelines for the Management of Acute Cervical Spinal Cord Injury, Neurosurgery 2013.
  4. Society of Critical Care Medicine (SCCM) Shock Management Guidelines, 2021.
  5. Tintinalli’s Emergency Medicine, 9th ed.