Swan-Ganz catheter location and left atrial pressure determine the accuracy of the wedge pressure when positive end-expiratory pressure is used.

In 43 percent of 30 consecutive open heart surgery patients, Swan-Ganz catheter tips lodged within 1 cm of or above the left atrium. When in this position the wedge pressure measured by the catheter was not an accurate estimate of left atrial pressure when positive end-expiratory pressure (PEEP) was used, especially when left atrial pressure was low. Catheters located below the left atrium were accurate at all levels of PEEP tested. The position of Swan-Ganz catheters should be confirmed by a lateral chest roentgenogram when PEEP is used, and catheter tips not below the left atrium should be repositioned.