Shock (Circulatory Shock): Types, Pathophysiology & Emergency Management

Shock (circulatory shock) is a life-threatening syndrome of inadequate tissue perfusion and oxygen delivery to meet metabolic demands — leading to cellular hypoxia, anaerobic metabolism, and multi-organ failure if uncorrected.

Four Major Types (Hinshaw/Cox Classification)

Type	Primary Defect	Key Causes	Hemodynamics (Typical)
Hypovolemic	↓ Preload (intravascular volume)	Hemorrhage, dehydration, burns, third-spacing (pancreatitis, sepsis)	↓ CO, ↓ PCWP, ↑ SVR
Cardiogenic	↓ Contractility (pump failure)	MI (most common), cardiomyopathy, arrhythmia, valvular rupture, myocarditis	↓ CO, ↑ PCWP, ↑ SVR
Distributive	↓ Afterload (vasodilation)	Septic (most common), anaphylactic, neurogenic (spinal cord injury), adrenal crisis	↑/↔ CO, ↓ PCWP, ↓ SVR
Obstructive	↑ Afterload / mechanical obstruction	Massive PE, cardiac tamponade, tension pneumothorax, aortic stenosis/dissection	↓ CO, ↑ PCWP (tamponade/PE), ↑ SVR

Unified Pathophysiology

↓ DO₂ (O₂ delivery) → tissue hypoxia → anaerobic glycolysis → lactic acidosis → cellular edema, mitochondrial dysfunction → endothelial activation → microvascular thrombosis, capillary leak → MODS.

Clinical Recognition (Early)

• Altered mental status, oliguria, cool/mottled extremities, tachycardia, hypotension (late), hyperlactatemia.
• Screening: qSOFA (RR≥22, SBP≤100, GCS<15), lactate >2 mmol/L.

Initial Resuscitation (First Hour — "Golden Hour")

1. Airway/Oxygen: Intubate if GCS≤8 or respiratory failure.
2. Access: 2 large-bore IVs or IO; arterial line, central line as needed.
3. Fluids: 30 mL/kg crystalloid bolus (hypovolemic, septic, obstructive). Caution in cardiogenic.
4. Vasopressors: Norepinephrine first-line (septic, distributive); dopamine alternative. Vasopressin add-on. Dobutamine for cardiogenic (inotropy).
5. Source Control: Antibiotics (septic), PCI (cardiogenic), thrombolysis/embolectomy (PE), pericardiocentesis (tamponade), chest tube (tension PTX), surgery (hemorrhage).
6. Monitor: Lactate clearance, ScvO₂, urine output, hemodynamics, end-organ function.

Shock is a dynamic process — frequent reassessment and protocolized bundles (Surviving Sepsis, ACC/AHA) improve survival.