A 38-year-old woman with severe burns (40% TBSA) is in hypovolemic shock with hypotension and oliguria. A 45-year-old man with acute pancreatitis is in distributive shock with hypotension but normal urine output. Which finding best distinguishes hypovolemic shock from distributive (septic/anaphylactic) shock?

Explanation

## Distinguishing Hypovolemic from Distributive Shock ### Hemodynamic and Clinical Comparison | Feature | Hypovolemic Shock | Distributive Shock (Septic/Anaphylactic) | |---------|-------------------|------------------------------------------| | **CVP** | ↓ Low (<2 mmHg) | ↑ Normal/Elevated (>8 mmHg) | | **PAWP** | ↓ Low | ↓ Low/Normal | | **SVR** | ↑ Elevated | ↓ Decreased | | **Cardiac Output** | ↓ Reduced | ↑ Normal/Elevated (early) | | **Skin Perfusion** | ↓ Cold, clammy | ↑ Warm, flushed (early sepsis) | | **Urine Output** | ↓ Oliguria | Normal or ↓ (if severe) | **Key Point:** Central venous pressure (CVP) is the single most discriminating parameter. Low CVP indicates absolute hypovolemia (blood/fluid loss), while normal or elevated CVP in shock indicates the problem is NOT intravascular volume depletion but rather maldistribution of volume (vasodilation) or cardiac dysfunction. ### Pathophysiologic Distinction **Hypovolemic Shock:** 1. Absolute loss of intravascular volume (hemorrhage, burns, dehydration) 2. ↓ Venous return → ↓ CVP 3. Sympathetic activation → ↑ SVR, vasoconstriction, cold extremities 4. Kidneys sense hypoperfusion → ↑ ADH, ↑ aldosterone → oliguria with low urine Na **Distributive Shock:** 1. Relative hypovolemia due to vasodilation (sepsis, anaphylaxis, pancreatitis) 2. Intravascular volume is present but maldistributed 3. CVP remains normal or elevated because the problem is not absolute volume loss 4. Early: warm extremities, normal/high CO; Late: cold extremities, ↓ CO **Clinical Pearl:** In burns (hypovolemic), aggressive fluid resuscitation targets a CVP of 8–12 mmHg to restore intravascular volume. In sepsis (distributive), a normal CVP may still be inadequate because of ongoing vasodilation; the target is higher CVP (12–15 mmHg) to overcome the vasodilatory state. **High-Yield:** CVP is the most readily available bedside marker of intravascular volume status. A low CVP in shock = hypovolemia. A normal/high CVP in shock = distributive or cardiogenic process. **Mnemonic:** **CVPS** — Central Venous Pressure is the Single best discriminator. [cite:Harrison 21e Ch 329]