Influence of lung injury on pulmonary wedge-left atrial pressure correlation during positive end-expiratory pressure ventilation.

The correlation between pulmonary artery wedge pressure (Pw) and left atrial pressure (Pla) requires a continuous fluid column between the catheter tip and the left atrium. We hypothesized that lung injury may protect the fluid column from the collapsing effects of increased airway pressure. Correlation between Pw and Pla would then depend on catheter tip location in injured versus normal lung regions. In 7 anesthetized dogs with unilateral acid pneumonitis, we compared Pla and simultaneous Pw measurements from pulmonary artery catheters located in injured and normal lungs at different levels of positive end-expiratory pressure (PEEP). Studies were repeated in 10 dogs with normal lungs and 5 dogs with bilateral acid pneumonitis. In supine dogs with unilateral lung injury, Pw from the injured lung more accurately reflected Pla than did Pw obtained from the normal lung at PEEP levels of 7 mmHg or higher, in contrast to data from dogs with normal lungs or equally injured lungs. Discrepancies between Pw and Pla at PEEP levels of 7 and 11 mmHg from the normal lung were corrected when that lung was placed in the dependent position to increase venous pressure at the catheter tip. A good Pw-Pla correlation was not guaranteed by catheter tip location below the level of the left atrium during PEEP ventilation. We conclude that the continuity of the fluid column was protected by lung injury. Although Pw-Pla differences from the normal lung were modest at the levels of PEEP that are usually optimal for gas exchange in uneven lung injury, it is recommended that the injured lung should not be avoided during insertion of the balloon-tipped catheter.