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Shock for USMLE Step 2

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Shock for the USMLE Step 2 Exam
Shock is a critical condition resulting from inadequate tissue perfusion and oxygenation, leading to cellular damage and organ dysfunction. Shock can be categorized into four main types: hypovolemic, distributive, cardiogenic, and obstructive.
signs and symptoms of shock
Types of Shock
Hypovolemic Shock
  • Etiology: Caused by a significant loss of intravascular volume, often due to hemorrhage (e.g., trauma, gastrointestinal bleeding) or fluid loss (e.g., vomiting, diarrhea, burns).
  • Pathophysiology: Decreased blood volume leads to reduced preload, decreased stroke volume, and ultimately reduced cardiac output, causing systemic hypoperfusion.
  • Clinical Features:
    • Signs: Tachycardia, hypotension, cool and clammy skin, delayed capillary refill.
  • Management:
    • Fluid Resuscitation: Rapid infusion of isotonic crystalloids (e.g., normal saline or lactated Ringer’s).
    • Blood Products: Indicated for significant hemorrhage to restore circulating volume and improve oxygen delivery.
Distributive Shock
Distributive shock is characterized by systemic vasodilation, leading to a relative intravascular volume deficit despite normal or increased total blood volume.
Septic Shock
  • Etiology: Severe infection (often bacterial) triggers systemic inflammation, leading to vasodilation and capillary leak.
  • Pathophysiology: Cytokine release decreases systemic vascular resistance (SVR) and increases capillary permeability, often resulting in high cardiac output and low SVR.
  • Clinical Features: Fever, tachycardia, hypotension, and warm skin in early stages, progressing to cool extremities as shock advances.
  • Management:
    • Antibiotics: Administer broad-spectrum antibiotics within one hour of diagnosis.
    • Fluid Resuscitation: Initial bolus of 30 mL/kg crystalloids.
    • Vasopressors: Norepinephrine is the first-line agent if hypotension persists after fluids.
Anaphylactic Shock
  • Etiology: IgE-mediated hypersensitivity reaction to allergens (e.g., foods, medications, insect stings).
  • Pathophysiology: Histamine and other mediators cause widespread vasodilation, increased vascular permeability, and bronchoconstriction.
  • Clinical Features: Angioedema, urticaria, hypotension, wheezing, and stridor.
  • Management:
    • Epinephrine: First-line treatment, administered intramuscularly.
    • Adjunctive Therapies: IV fluids, antihistamines, and corticosteroids to control symptoms and prevent recurrence.
Cardiogenic Shock
  • Etiology: Results from cardiac pump failure, often due to acute myocardial infarction (MI), severe heart failure, valvular disease, or arrhythmias.
  • Pathophysiology: Impaired myocardial contractility decreases cardiac output, leading to elevated filling pressures and systemic hypoperfusion.
  • Clinical Features: Hypotension, tachycardia, jugular venous distention, pulmonary crackles, cool extremities.
  • Management:
    • Inotropes: Dobutamine or milrinone to enhance myocardial contractility.
    • Vasopressors: Norepinephrine for blood pressure support in cases of severe hypotension.
    • Revascularization: Percutaneous coronary intervention (PCI) or thrombolysis for patients with MI.
Obstructive Shock
Obstructive shock occurs due to a physical obstruction to blood flow, reducing cardiac output despite normal myocardial function.
  • Etiology:
    • Pulmonary Embolism (PE): Causes right ventricular (RV) outflow obstruction.
    • Tension Pneumothorax: Increased intrathoracic pressure compresses the heart and great vessels.
    • Cardiac Tamponade: Accumulated pericardial fluid compresses the heart, limiting ventricular filling.
  • Clinical Features:
    • PE: Sudden dyspnea, pleuritic chest pain, signs of RV strain.
    • Tension Pneumothorax: Unilateral chest pain, absent breath sounds, tracheal deviation.
    • Cardiac Tamponade: Beck’s triad (hypotension, jugular venous distention, muffled heart sounds).
  • Management:
    • PE: Anticoagulation, with thrombolysis in massive PE cases.
    • Tension Pneumothorax: Immediate needle decompression, followed by chest tube insertion.
    • Cardiac Tamponade: Emergency pericardiocentesis.
Key Points
  • Types of Shock:
    • Hypovolemic: Due to fluid loss; treated with crystalloids and blood transfusion if hemorrhagic.
    • Distributive: Characterized by vasodilation (e.g., septic, anaphylactic shock); managed with fluids and vasopressors.
    • Cardiogenic: Caused by heart pump failure; managed with inotropes, vasopressors, and revascularization for MI.
    • Obstructive: Due to mechanical obstruction (e.g., PE, tension pneumothorax, cardiac tamponade); treated by relieving the obstruction.
  • Hemodynamics:
    • CVP: Low in hypovolemic shock; elevated in cardiogenic and obstructive shock.
    • SVR: Decreased in distributive shock; increased in hypovolemic and cardiogenic shock.
  • Management:
    • Fluid Resuscitation: Primary therapy in hypovolemic and distributive shock.
    • Vasopressors: Norepinephrine is first-line in septic and neurogenic shock.
    • Inotropes: Used in cardiogenic shock to improve cardiac output.

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