Hemodynamic Monitoring

The pulmonary artery (PA) catheter (Swan-Ganz) is a balloon-tipped catheter floated from a central vein through the right heart and into the PA. It measures intracardiac and PA pressures and cardiac output.

Normal pressures: - CVP (RA): 2–6 mmHg - RV: 25/5 mmHg - PA systolic/diastolic: 25/8 mmHg; mean PA: 8–20 mmHg - PCWP (wedge): 6–12 mmHg

The wedge pressure (PCWP) reflects left atrial pressure and left ventricular preload. PCWP >18 mmHg suggests cardiogenic pulmonary edema; PCWP ≤18 mmHg in ARDS indicates non-cardiogenic cause.

Cardiac output (CO) = HR × Stroke Volume. Normal CO: 4–8 L/min. Cardiac index (CI) normalizes for body size: CI = CO / BSA; normal 2.4–4.0 L/min/m².

Derived hemodynamic parameters: - SVR (systemic vascular resistance): normal 800–1200 dyn·s·cm⁻⁵ SVR = (MAP – CVP) / CO × 80 - PVR (pulmonary vascular resistance): normal <250 dyn·s·cm⁻⁵ PVR = (mPAP – PCWP) / CO × 80 - SvO2 (mixed venous O2 saturation): normal 60–75%; low SvO2 = inadequate delivery - DO2 (oxygen delivery): CaO2 × CO × 10; normal 950–1150 mL/min - VO2 (oxygen consumption): normal 200–250 mL/min

Different shock states produce characteristic hemodynamic profiles:

Cardiogenic shock: ↓CO, ↑PCWP, ↑SVR, ↓SvO2 (heart can't pump, backs up fluid, vasoconstricts)

Distributive/septic shock: ↑CO (early), ↓SVR, ↓PCWP, ↓SvO2 or ↑SvO2 (vasodilation, high flow but poor extraction)

Hypovolemic shock: ↓CO, ↓PCWP, ↑SVR, ↓SvO2 (low volume, vasoconstricts to compensate)

Obstructive shock (PE/tension PTX): ↓CO, ↑PCWP (right side), ↑PVR, ↓SvO2

Mnemonic: ARDS: ↑ PA pressures, normal or low PCWP (non-cardiogenic); elevated PVR.