Overview
This lecture explains the main types of shock, their pathophysiology, distinguishing features, diagnostic approaches, complications, and treatment strategies for each category.
Types of Shock
- Four main types of shock: hypovolemic, obstructive, distributive, and cardiogenic.
- Shock results in decreased tissue perfusion and can lead to multi-organ failure.
Hypovolemic Shock
- Caused by loss of blood (hemorrhage) or fluids (vomiting, diarrhea, burns, diuretics).
- Leads to decreased venous return, preload, stroke volume, cardiac output, and blood pressure.
- Results in reduced organ perfusion and dysfunction.
Obstructive Shock
- Caused by physical obstruction to heart filling or blood outflow (e.g., tamponade, tension pneumothorax, pulmonary embolism).
- Reduces preload (venous return) or increases afterload, dropping cardiac output and perfusion.
Distributive Shock
- Characterized by massive vasodilation and low systemic vascular resistance (SVR).
- Common causes: septic shock (infection/cytokine release), neurogenic shock (loss of sympathetic tone), anaphylactic shock (allergic reaction).
- Typically presents with warm, red skin due to vasodilation.
Cardiogenic Shock
- Results from impaired heart contractility (e.g., MI, acute heart failure, severe valvular regurgitation) or arrhythmias (too slow/fast heart rate).
- Reduces stroke volume, cardiac output, and mean arterial pressure, leading to organ hypoperfusion.
Clinical Features and Complications
- Cardiogenic, obstructive, and hypovolemic shocks: cold, pale, mottled extremities due to vasoconstriction.
- Distributive shock: warm, pink/red, well-perfused skin.
- All shocks may cause lactic acidosis, encephalopathy, kidney injury, mesenteric ischemia, ischemic hepatitis.
- Reflex tachycardia common except in neurogenic shock and severe bradyarrhythmias.
Diagnostic Approach
- Shock index: heart rate divided by systolic BP; >1 suggests shock.
- Elevated lactate, evidence of organ dysfunction (troponin, creatinine, LFTs, mental status).
- Right heart catheterization (Swan-Ganz) helps differentiate shock types via cardiac index, SVR, CVP, and pulmonary capillary wedge pressure.
Treatment Strategies
- Hypovolemic: IV fluids for fluid loss, blood transfusion for hemorrhage.
- Obstructive: treat cause (pericardiocentesis for tamponade, chest tube for pneumothorax, TPA or embolectomy for PE).
- Cardiogenic: treat underlying cause (PCI for MI, valve replacement, pacemaker for bradycardia, reverse drug toxicities), inotropes or mechanical support if needed.
- Distributive: epinephrine for anaphylaxis, antibiotics and fluids for sepsis, vasopressors (norepinephrine, vasopressin, phenylephrine) to support BP.
Key Terms & Definitions
- Preload — volume of blood entering the heart before contraction.
- Afterload — resistance the heart must overcome to pump blood out.
- Systemic Vascular Resistance (SVR) — resistance in blood vessels impacting BP.
- Cardiac Output (CO) — amount of blood pumped by the heart per minute.
- Mean Arterial Pressure (MAP) — average pressure in arteries during one cardiac cycle.
- CVP (Central Venous Pressure) — pressure in the thoracic vena cava near the right atrium.
- Pulmonary Capillary Wedge Pressure (PCWP) — indirect measure of left atrial pressure.
- Distributive Shock — shock due to vascular dilation and decreased SVR.
- Shock Index — ratio of heart rate to systolic blood pressure.
Action Items / Next Steps
- Review the pathophysiology, diagnostic criteria, and treatments for each type of shock.
- Study differentiating features of shock types (physical signs, hemodynamics).
- Practice calculating shock index and interpreting catheterization data.