Causes and types of shock

1. Definition

• Shock = life-threatening systemic hypoperfusion → inadequate tissue oxygenation. Caused by ↓cardiac output, ↓circulating volume, or peripheral vasodilation.
• Results: severe hypotension, generalized tissue hypoxia, multi-organ dysfunction; intense sympathetic activity → capillary stasis, cellular hypoxia, acidosis.
• Early = reversible injury; late = irreversible necrosis → death.

2. Types of Shock

Type	Mechanism	Examples
Cardiogenic	Pump failure / ↓CO	MI, arrhythmia, myocarditis, cardiomyopathy; outflow (PE) / filling (tamponade) failure
Hypovolemic	↓ effective volume	Hemorrhage, burns, vomiting/diarrhea, DKA/DI
Anaphylactic	Type I (IgE) → histamine → vasodilation + ↑permeability	Allergen/drug exposure
Neurogenic	Loss of vascular tone	Spinal cord injury (vasodilation + bradycardia)
Septic	Endothelial damage from infection	Gram− endotoxin (LPS/lipid A)

3. Pathogenesis of Septic Shock

• PAMPs → Toll-like receptors → cytokine storm (IL-1, TNF, PGs, ROS, PAF) → endothelial activation/injury:
  • Pro-coagulant → DIC; vasodilation → hypoperfusion; ↑permeability → edema.
• Metabolic: ↓insulin/↑resistance → hyperglycemia → impaired neutrophils. Glucocorticoid depletion → adrenal insufficiency.
• Consequences: multi-organ failure — kidney (acute tubular necrosis, medullary hypoxia), lung (ARDS / diffuse alveolar damage), adrenal lipid depletion, GI mucosal hemorrhage/necrosis.

4. Stages of Shock

1. Non-progressive (reversible): compensatory RAAS, catecholamines, ADH, sympathetic reflex → tachycardia, vasoconstriction, fluid retention; vital organs perfused.
2. Progressive: widespread hypoxia → anaerobic glycolysis → lactic acidosis → arteriolar dilation, blood pooling, worsening CO.
3. Irreversible: lysosomal enzyme leak, ischemic bowel → endotoxemia, ATN-renal failure → death.

💡 High-yield: Cardiogenic/hypovolemic/obstructive → ↓CO + ↑SVR (cold, clammy); distributive (septic/anaphylactic/neurogenic) → ↓SVR (warm early). Septic shock = TLR-driven cytokine storm → DIC + ARDS + ATN. Stages: non-progressive → progressive → irreversible.