Hemodynamic Monitoring

A CVP of 2 mmHg and a wedge pressure of 18 mmHg point to completely different problems — but both come from the same catheter. Knowing how to read these numbers separates reaction from recognition.

Hemodynamic monitoring uses invasive and noninvasive tools to quantify cardiac function and tissue perfusion. The pulmonary artery (Swan-Ganz) catheter measures four key pressures: CVP (right atrial pressure, normal 2–6 mmHg), PA pressure (systolic 15–25, diastolic 8–15 mmHg), pulmonary artery wedge pressure (PAWP, normal 6–12 mmHg reflecting left ventricular preload), and cardiac output (4–8 L/min). Arterial lines provide continuous blood pressure and access for ABG sampling — the mean arterial pressure (MAP) target is ≥65 mmHg to maintain organ perfusion. When interpreting values, think in a circuit: CVP reflects right-sided preload, PAWP reflects left-sided preload, and systemic vascular resistance (SVR, normal 800–1200 dynes·sec/cm⁵) reflects afterload. A low CVP with low PAWP suggests volume depletion. A high PAWP with low cardiac output suggests pump failure. Nursing responsibilities include leveling the transducer at the phlebostatic axis (4th intercostal space, mid-axillary line), zeroing the system to atmospheric pressure before readings, and obtaining values at end-expiration for accuracy. Never inflate the balloon for more than 15 seconds during wedge readings — prolonged inflation risks pulmonary artery rupture.

Key Distinctions

Don't confuse CVP (right heart preload) with PAWP (left heart preload) — a normal CVP does not rule out left-sided failure. Students mix up SVR (afterload, resistance) with cardiac output (forward flow) — SVR rises as compensation when CO drops, not the reverse. Arterial line MAP is more reliable than cuff readings in shock states; a cuff pressure can underestimate true perfusion pressure.

Clinical Pearl

Level, zero, read at end-expiration. If the transducer drifts off the phlebostatic axis by even 1 inch, your numbers lie — and your interventions follow a lie.