Overview
This lecture covers the types, pathophysiology, complications, diagnostic approach, and treatments of shock, emphasizing key features and differences between shock subtypes.
Types of Shock
- Four main types: hypovolemic, obstructive, distributive, and cardiogenic shock.
- Hypovolemic shock is due to fluid or blood loss (e.g., vomiting, diarrhea, burns, trauma).
- Obstructive shock results from physical blockage (e.g., tension pneumothorax, cardiac tamponade, pulmonary embolism).
- Distributive shock is caused by massive vasodilation (e.g., septic shock, neurogenic shock, anaphylactic shock).
- Cardiogenic shock arises from poor heart contractility or arrhythmias (MI, acute heart failure, valve regurgitation, tachy/bradyarrhythmias).
Pathophysiology & Clinical Features
- All shock types result in decreased tissue perfusion and organ dysfunction.
- Hypovolemic, obstructive, and cardiogenic shocks: decreased cardiac output, increased systemic vascular resistance (SVR), cold/pale/mottled extremities, reflex tachycardia (except bradyarrhythmias).
- Distributive shock: decreased SVR, increased cardiac output, warm/flushed extremities, reflex tachycardia (except neurogenic shock with bradycardia).
- Organ malperfusion causes lactic acidosis, encephalopathy, acute kidney injury, myocardial ischemia, mesenteric ischemia, and ischemic hepatitis.
Diagnosis
- Shock index = heart rate / systolic BP; >1 suggests shock.
- Elevated lactate indicates poor tissue perfusion.
- Assess for signs of organ dysfunction (e.g., altered mental status, chest pain, reduced urine output).
- Hemodynamic monitoring (Swan-Ganz catheter) distinguishes shock types using cardiac index, SVR, CVP, and pulmonary capillary wedge pressure.
Management by Shock Type
- Hypovolemic: Replace missing fluids (IV fluids or blood).
- Obstructive: Relieve obstruction (e.g., pericardiocentesis, chest tube, thrombolysis/embolism removal).
- Cardiogenic: Treat cardiac cause (e.g., cath lab for MI, valve surgery, pacemaker, cardioversion, inotropes if needed).
- Distributive: Treat underlying cause (antibiotics for sepsis, epinephrine for anaphylaxis, vasopressors to increase SVR).
Key Terms & Definitions
- Shock — Life-threatening state of inadequate tissue perfusion and oxygenation.
- Hypovolemic shock — Due to fluid or blood loss.
- Obstructive shock — Due to physical obstruction impeding blood flow.
- Distributive shock — Due to widespread vasodilation and low SVR.
- Cardiogenic shock — Due to pump failure from the heart.
- SVR (Systemic Vascular Resistance) — Resistance in blood vessels against which the heart pumps.
- MAP (Mean Arterial Pressure) — Average arterial pressure during a single cardiac cycle.
- Swan-Ganz catheter — Device for measuring heart and lung pressures.
Action Items / Next Steps
- Review the subtypes of shock and their distinguishing features.
- Practice identifying shock types based on clinical scenarios.
- Memorize core diagnostic values (shock index, SVR, cardiac index).
- Complete any assigned reading on shock complications and management protocols.