Lateral position improves wedge-left atrial pressure correlation during positive-pressure ventilation.

Because lateral position can be used to locate a pulmonary artery catheter tip in lung regions where venous pressure exceeds alveolar pressure, we studied the effect of lateral position on the correlation between pulmonary artery occlusion pressure (Pw) and left atrial pressure (Pla) at various increments of positive-end expiratory pressure (PEEP). In ten normal anesthetized pigs, catheters were placed in the left atrium and right and left pulmonary arteries; simultaneous measurements of Pla and Pw from both catheters were obtained in the supine, right lateral, and left lateral positions. Pw obtained in the lateral position when the catheter tip was vertically located below the left atrium ("lower") more accurately reflected Pla changes than Pw obtained from catheters above the left atrium, at PEEP levels less than 20 cm H2O. Although most catheter tips were located below the left atrium in the supine position, our data from the lower catheter more accurately assessed Pla than did the Pw obtained in the supine position; this was particularly evident when the catheter tip was located vertically above the left atrium. These findings suggest that the lateral position can be useful in measuring Pw during continuous positive-pressure ventilation. However, further studies in humans are needed before this maneuver can be recommended.