A 52-year-old man with acute myocardial infarction presents with hypotension (SBP 85 mmHg), elevated JVP, and clear lung fields. A second patient with septic shock from pneumonia presents with hypotension (SBP 80 mmHg), normal JVP, and pulmonary crackles. Which single feature best distinguishes cardiogenic shock from septic shock?

Explanation

## Distinguishing Cardiogenic from Septic Shock ### Hemodynamic Profile Comparison | Parameter | Cardiogenic Shock | Septic Shock | |-----------|-------------------|---------------| | **SVR** | ↑ Elevated | ↓ Decreased | | **Cardiac Output** | ↓ Reduced | ↑ Elevated (early) or ↓ (late) | | **PAWP** | ↑ Elevated | Normal or ↓ | | **JVP** | ↑ Elevated | Normal | | **Lactate** | ↑ (due to hypoperfusion) | ↑ (due to mitochondrial dysfunction) | **Key Point:** Systemic vascular resistance (SVR) is the single most discriminating hemodynamic parameter. In cardiogenic shock, the body compensates for reduced cardiac output by vasoconstriction (↑ SVR). In septic shock, endotoxins and inflammatory mediators cause vasodilation (↓ SVR), despite elevated cardiac output in early phases. ### Pathophysiologic Basis **Cardiogenic Shock:** 1. Myocardial pump failure → ↓ CO 2. Baroreceptor reflex → sympathetic activation 3. Result: ↑ SVR, ↑ afterload, ↑ JVP, pulmonary edema **Septic Shock:** 1. Bacterial endotoxin → TNF-α, IL-1, IL-6 release 2. Nitric oxide-mediated vasodilation → ↓ SVR 3. Myocardial depression (cytokine-induced) → ↓ contractility 4. Result: ↓ SVR, normal/high CO initially, normal JVP **Clinical Pearl:** The elevated JVP in cardiogenic shock reflects right ventricular dysfunction and elevated right atrial pressure, whereas in septic shock JVP remains normal because the primary problem is peripheral vasodilation, not cardiac filling. **High-Yield:** SVR calculation: $SVR = \frac{(MAP - CVP) \times 80}{CO}$ — this is the physiologic hallmark that separates these two shock states on hemodynamic monitoring. [cite:Harrison 21e Ch 329]