obstructive shock
Summary
Shock state caused by mechanical obstruction to cardiac filling or outflow, producing reduced cardiac output despite normal myocardial function. Classic causes: cardiac tamponade, tension pneumothorax, and massive pulmonary embolism.
Detail
Hemodynamic signature: low cardiac output and low mixed venous oxygen saturation with high systemic vascular resistance, similar to cardiogenic shock. Preload markers depend on cause - JVP/CVP are elevated in tamponade and tension pneumothorax (impaired filling) and in massive PE (acute cor pulmonale with elevated right-sided pressures), while left-sided wedge pressure may be low. Bedside clues: Beck triad (hypotension, muffled heart sounds, JVD) in tamponade with pulsus paradoxus; tracheal deviation away from the affected side and absent breath sounds in tension pneumothorax; sudden dyspnea, hypoxemia, and S1Q3T3 in massive PE. Treatment is mechanical: pericardiocentesis, needle/finger thoracostomy, and thrombolysis or embolectomy respectively.
Sources
- First Aid for USMLE Step 2 CK
- Harrison's Principles of Internal Medicine
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