Hemodynamic Monitoring and Interpretation
Core concepts
Hemodynamic interpretation is the highest-yield reasoning domain. You must understand pressure waveforms, normal values, and how to derive and interpret cardiac output, vascular resistance, and shunt calculations.
Key normal pressures: right atrium 2–6 mm Hg, right ventricle systolic 15–30/diastolic 0–8, pulmonary artery 15–30/4–12 with mean 10–20, and pulmonary capillary wedge pressure (PCWP) 6–12 mm Hg. Left ventricular end-diastolic pressure approximates PCWP. Cardiac output is typically 4–8 L/min; cardiac index 2.5–4.0 L/min/m².
Derived values use standard formulas: mean arterial pressure = (SBP + 2×DBP)/3; cardiac index = CO/BSA; systemic vascular resistance = (MAP − CVP) × 80 / CO; pulmonary vascular resistance = (mean PA − PCWP) × 80 / CO. Fick principle: CO = oxygen consumption / arteriovenous oxygen difference.
Interpret patterns: cardiogenic shock shows low CO, high PCWP, high SVR. Septic shock shows high CO, low SVR, low-to-normal filling pressures. Right heart failure shows elevated RA and RV pressures with low PA pulsatility. Cardiac tamponade shows equalization of diastolic pressures and a blunted y descent. Constrictive pericarditis shows prominent y descent and ventricular interdependence.
Traps
Watch units and whether a value is mean or systolic. Do not confuse PCWP with PA diastolic pressure, though they approximate when pulmonary resistance is normal. Remember the ×80 conversion factor in resistance formulas. Shunt questions require the Qp/Qs ratio using oxygen saturations.
Worked example
CO 4 L/min, MAP 70, CVP 5: SVR = (70 − 5) × 80 / 4 = 1300 dyn·s·cm⁻⁵, a normal-to-high value consistent with vasoconstriction.