What is Neurogenic Shock?
Neurogenic shock is a distributive type of circulatory shock caused by loss of sympathetic tone following spinal cord injury, resulting in widespread vasodilation, hypotension, and characteristically bradycardia (unlike other shock states). 1
Pathophysiology
Neurogenic shock occurs when spinal cord injury—typically at the cervical or high thoracic level—disrupts descending sympathetic pathways. This creates an imbalance between sympathetic and parasympathetic regulation of vascular smooth muscle, leading to:
- Generalized vasodilation with loss of peripheral vascular resistance
- Relative hypovolemia from pathological redistribution of blood volume (not true volume loss)
- Bradycardia from unopposed parasympathetic (vagal) tone
- Inadequate tissue perfusion despite the distributive (high-flow) nature 1
The hemodynamic profile is more complex than traditionally described. Research shows neurogenic shock represents a spectrum of mechanisms rather than a single pattern—decreased peripheral vascular resistance (33% of cases), loss of vascular capacitance (22%), mixed resistance and capacitance problems (33%), or even purely cardiac dysfunction (11%) 2. This heterogeneity explains why patients respond differently to standard treatments.
Clinical Presentation
The classic triad distinguishing neurogenic from other shock types:
- Hypotension (systolic BP typically <90 mmHg, MAP <65 mmHg)
- Bradycardia or inappropriate lack of tachycardia (this is the key differentiator—other shock types cause compensatory tachycardia) 3
- Warm, dry skin from peripheral vasodilation (versus cold, clammy skin in hypovolemic/cardiogenic shock)
Additional features consistent with the general definition of shock 4:
- Altered mental status
- Decreased urine output
- Elevated lactate (>2 mmol/L)
- Evidence of spinal cord injury on examination
Incidence and Epidemiology
The reported incidence varies dramatically (from 14% to 44%) depending on diagnostic criteria used, highlighting a critical problem in the literature 5. Using rigorous combined hemodynamic and laboratory criteria, the true incidence is approximately 29% in cervical spinal cord injuries 5. The inconsistency stems primarily from failure to distinguish neurogenic shock from simple hypovolemia in trauma patients.
Critical Diagnostic Pitfall
Do not confuse hypovolemic shock (from bleeding) with neurogenic shock in trauma patients—both cause hypotension, but hypovolemic shock causes tachycardia while neurogenic shock causes bradycardia or relative bradycardia 5. Many patients have both conditions simultaneously, requiring careful assessment.
Clinical Course
Blood pressure characteristically shows a biphasic pattern: initial hypotension at presentation, followed by a secondary decline during the first week post-injury 5. This delayed deterioration is often underappreciated and requires continued vigilance beyond the immediate post-injury period.
Microcirculatory dysfunction is present in 92% of patients during the acute phase, with 47% still showing abnormalities at day 7, and this correlates with in-hospital mortality 6.
Life-Threatening Nature
Neurogenic shock is a life-threatening emergency that: