If PEEP is 15-20 cmH2O, which measurement should be watched?

• A. MAP
• B. HR
• C. PCWP
• D. SpO2

Answer: (C)

When PEEP is high, intrathoracic pressure rises and this alters venous return and the pressures the heart experiences, especially on the left side. The measurement that best reflects left-sided filling pressures in this situation is the pulmonary capillary wedge pressure, which estimates left atrial pressure and hence left-sided preload. Monitoring PCWP helps you assess for pulmonary edema risk and guide fluid management or diuretic therapy under high PEEP.

If PCWP is elevated, it suggests increased left atrial pressure and a greater risk of edema, meaning fluid removal or vasodilator strategies might be considered. If PCWP is low or normal, the problem may be more about preload deficiency or non-cardiogenic factors rather than left-sided hypertension. In contrast, mean arterial pressure indicates overall perfusion, heart rate is a general hemodynamic marker, and oxygen saturation shows oxygenation—none directly pinpoints left-sided filling pressures like PCWP does. Remember that high PEEP can artificially raise wedge pressures due to increased intrathoracic pressure, so interpret PCWP within the broader hemodynamic context.