How does hypocortisolism cause shock?

Pathophysiology of Shock in Hypocortisolism

Hypocortisolism causes shock primarily through progressive loss of vasomotor tone and impaired alpha-adrenergic receptor responses to noradrenaline, leading to vasodilation, hypotension, and ultimately fatal shock if not rapidly corrected. 1

Mechanisms of Shock Development

Primary Vascular Effects

• Cortisol deficiency leads to:
  • Progressive loss of vascular tone
  • Impaired alpha-adrenergic receptor responses to noradrenaline
  • Decreased sensitivity to vasopressors
  • Reduced effectiveness of endogenous catecholamines 1

Progression of Hemodynamic Compromise

The progression of shock in hypocortisolism follows a predictable pattern:

1. Orthostatic hypotension (early sign)
2. Supine hypotension (intermediate sign)
3. Refractory shock (late sign)
4. Death if not corrected 1

Fluid and Electrolyte Disturbances

• Hypocortisolism affects fluid and electrolyte balance through:
  • Impaired water excretion (especially problematic post-surgery)
  • Hyponatremia (due to water retention and inadequate aldosterone)
  • Hyperkalemia (particularly in primary adrenal insufficiency) 1
  • Reduced effective circulating volume 1

Critical Illness-Related Corticosteroid Insufficiency (CIRCI)

In critical illness, relative adrenal insufficiency (RAI) or CIRCI can develop, characterized by:

• Inadequate cortisol response to stress
• Volume-resistant hypotension
• Vasopressor dependency 1

This occurs in:

• 68.9% of critically ill patients with sepsis or septic shock
• 41.8% of non-critically ill cirrhotic patients 1

Contributing Factors to Adrenal Dysfunction in Critical Illness

Several mechanisms contribute to adrenal dysfunction during critical illness:

• Suppression of the hypothalamic-pituitary-adrenal axis
• Reduced effective volemia impairing adrenal perfusion
• Impaired cholesterol synthesis (substrate for steroid production)
• Enhanced pro-inflammatory cytokine production 1
• Increased volume of distribution of cortisol 1

Clinical Manifestations of Impending Adrenal Crisis

Early recognition is crucial as volume-resistant hypotension may be a late or even agonal event. Watch for:

1. Non-specific malaise
2. Somnolence or obtunded consciousness
3. Cognitive dysfunction
4. Orthostatic hypotension (early sign)
5. Supine hypotension (more advanced)
6. Shock resistant to fluid resuscitation 1

Specific Populations at Risk

Certain populations are at higher risk of adrenal insufficiency and subsequent shock:

• Patients with purpura fulminans and Waterhouse-Friderichsen syndrome
• Those previously on chronic steroid therapy
• Patients with pituitary or adrenal abnormalities
• Children with trisomy 21 or CNS pathology 1
• Patients receiving etomidate (inhibits 11-beta-hydroxylase) 1

Treatment Considerations

While not the focus of the question, it's worth noting that treatment involves:

• Prompt administration of hydrocortisone (typically 100mg IV initially)
• Continuous infusion is preferred over bolus dosing for maintaining stable plasma cortisol levels 1, 2
• Fluid resuscitation to restore effective circulating volume
• Vasopressors may be required until cortisol replacement takes effect

Pitfalls in Recognition and Management

• Relying solely on blood pressure: Orthostatic hypotension often precedes frank shock
• Delayed recognition: Non-specific symptoms may be attributed to other causes
• Inadequate treatment: Insufficient cortisol replacement can lead to persistent shock
• Failure to consider mineralocorticoid effects: In primary adrenal insufficiency, both cortisol and aldosterone are affected 2

Understanding the pathophysiology of hypocortisolism-induced shock is essential for prompt recognition and appropriate management to prevent progression to fatal shock.