A 52-year-old man with acute myocardial infarction develops hypotension, tachycardia, and cold extremities. His pulmonary capillary wedge pressure (PCWP) is elevated at 22 mmHg. Which single feature best distinguishes cardiogenic shock from hypovolemic shock in this patient?

Explanation

## Distinguishing Cardiogenic from Hypovolemic Shock ### Pathophysiologic Basis Cardiogenic and hypovolemic shock both present with hypotension, tachycardia, and tissue hypoperfusion, but their hemodynamic profiles differ fundamentally. ### Hemodynamic Comparison | Feature | Cardiogenic Shock | Hypovolemic Shock | |---------|-------------------|-------------------| | **PCWP** | ↑ Elevated (>18 mmHg) | ↓ Low (<8 mmHg) | | **CVP** | ↑ Elevated (>8 mmHg) | ↓ Low (<2 mmHg) | | **Cardiac Output** | ↓ Decreased | ↓ Decreased | | **SVR** | ↑ Increased | ↑ Increased | | **Pulmonary edema** | Present | Absent | | **Urine output** | Oliguria | Oliguria | **Key Point:** Elevated PCWP (pulmonary capillary wedge pressure) is the **hallmark discriminator** of cardiogenic shock. It reflects backward transmission of elevated left ventricular end-diastolic pressure due to pump failure. In hypovolemic shock, PCWP remains low because the problem is insufficient circulating volume, not myocardial dysfunction. ### Clinical Pearl In cardiogenic shock, the heart cannot eject blood effectively → blood backs up into the lungs → pulmonary edema develops. In hypovolemic shock, there is simply not enough blood to fill the circulation → all pressures (CVP, PCWP) are low. **High-Yield:** PCWP measurement via Swan-Ganz catheter is the gold standard for hemodynamic differentiation. PCWP >18 mmHg in shock = cardiogenic; PCWP <8 mmHg = hypovolemic. ### Why Other Features Are Non-Discriminatory Tachycardia, vasoconstriction, acidosis, and oliguria occur in **both** types of shock as compensatory responses to tissue hypoperfusion. They are universal shock features, not discriminators.