Shock Classification

Shock classification is based on the underlying mechanism and hemodynamic profile. Understanding the hemodynamic parameters (cardiac output [CO], systemic vascular resistance [SVR], central venous pressure [CVP], and pulmonary artery occlusion pressure [PAOP/wedge]) guides treatment: (1) Hypovolemic shock: ↓CO, ↑SVR (compensatory vasoconstriction), ↓CVP, ↓PAOP — treatment: volume replacement. (2) Cardiogenic shock: ↓CO, ↑SVR (compensatory), ↑CVP, ↑PAOP (backup of blood behind failing ventricle) — treatment: inotropes, vasopressors, reduce afterload, reperfusion for MI. (3) Distributive shock (septic, anaphylactic, neurogenic): initially ↑CO (hyperdynamic), ↓SVR (vasodilation — the primary defect), ↓CVP (relative hypovolemia) — treatment: fluids + vasopressors. Late septic shock may have ↓CO from myocardial depression. (4) Obstructive shock: ↓CO (mechanical obstruction to filling or ejection), ↑SVR, variable CVP (↑ in tamponade/PE, ↓ in tension pneumothorax with mediastinal shift) — treatment: relieve the obstruction. Tissue oxygenation assessment: ScvO2 >70% in early septic shock (cells cannot extract O2 — cytopathic hypoxia) vs. ScvO2 <60% in cardiogenic/hypovolemic shock (increased O2 extraction from low cardiac output).