A comparison of pulmonary artery occlusion pressure and left ventricular end-diastolic pressure during mechanical ventilation with PEEP in patients with severe ARDS.

When positive end-expiratory pressure (PEEP) is applied to normal lungs, the pulmonary artery occlusion pressure (PAOP) may reflect alveolar pressure and not left ventricular end-diastolic pressure (LVEDP). The reliability of PAOP measurements has been questioned when PEEP levels greater than 10 cm H2O are applied. To verify whether this disparity occurs in patients with severe lung injury, the authors simultaneously measured both PAOP and LVEDP at 0, 10, and 16-20 cm H2O PEEP in 12 supine patients with severe adult respiratory distress syndrome (ARDS). In all patients, the radiographic location of the PA catheter tip was at or below the level of the posterior border of the left atrium. A close correlation was found between PAOP and LVEDP at each level of PEEP. In only six of 35 simultaneous measurements was the PAOP-LVEDP gradient 2 mmHg or more (2-3 mmHg in four, and 4 mmHg in two). In five patients, the highest PEEP level was 4-9 cm H2O greater than LVEDP; however, no gradient was measured between LVEDP and PAOP. The authors conclude that, in severe ARDS, a close correspondence between PAOP and LVEDP is maintained despite applying PEEP levels up to 20 cm H2O, suggesting that, in ARDS, surrounding pathology prevents transmitted alveolar pressure from collapsing adjacent pulmonary vessels.