Intracardiac pressures PA catheter and tailored therapy

• Transmural pressure (≈ preload) = measured intracardiac pressure – intrathoracic pressure

• Intrathoracic pressure (usually slightly ⊖) is transmitted to vessels and heart

• Always measure intracardiac pressure at end-expiration, when intrathoracic pressure closest to 0 (“high point” in spont. breathing Pts; “low point” in Pts on ⊕ pressure vent.)

• If ↑ intrathoracic pressure (eg, PEEP), measured PCWP overestimates true transmural pressures. Can approx by subtracting ~½ PEEP (× ¾ to convert cm H2O to mmHg).

• PCWP: LV preload best estimated at a wave; risk of pulm edema driven by avg PCWP