Which statement about the pulmonary capillary wedge pressure is true?

Which statement about the pulmonary capillary wedge pressure is true?

• A. It is identical to right atrial pressure
• B. It directly measures left atrial pressure
• C. It is obtained from the pulmonary artery without wedging
• D. It estimates left atrial pressure and left-sided filling pressures

Answer: (D)

Pulmonary capillary wedge pressure provides an estimate of left atrial pressure and left-sided filling pressures because when a balloon-tipped catheter is wedged in a small pulmonary artery branch, the pressure measured beyond the balloon reflects the pressure in the pulmonary capillaries and, via the pulmonary veins, the left atrium. It is an indirect surrogate, not a direct measurement of left atrial pressure. It is not identical to right atrial pressure, which reflects systemic venous pressure. And you can’t obtain a wedge pressure without wedging the catheter—the balloon must occlude a branch to stop antegrade flow and equilibrate with the left atrial pressure.

Pulmonary capillary wedge pressure provides an estimate of left atrial pressure and left-sided filling pressures because when a balloon-tipped catheter is wedged in a small pulmonary artery branch, the pressure measured beyond the balloon reflects the pressure in the pulmonary capillaries and, via the pulmonary veins, the left atrium. It is an indirect surrogate, not a direct measurement of left atrial pressure. It is not identical to right atrial pressure, which reflects systemic venous pressure. And you can’t obtain a wedge pressure without wedging the catheter—the balloon must occlude a branch to stop antegrade flow and equilibrate with the left atrial pressure.