Central venous pressure and pulmonary capillary wedge pressure as estimates of left atrial pressure: effects of positive end-expiratory pressure and catheter tip malposition.

We compared CVP and pulmonary capillary wedge pressure (WP) measurements with left atrial pressure (LAP) in postcoronary bypass surgical patients with preserved cardiopulmonary function. Measurements were obtained under normal conditions and conditions likely to induce WP-LAP discrepancies (PEEP and catheter tip malposition). Patients were in both supine and lateral positions; the catheter tip was placed vertically below (tip down; n = 12) or above (tip up; n = 5) the left atrium. Our data showed that both CVP and WP correlated well with LAP at all PEEP levels in the supine and tip down lateral positions. However, in the tip up lateral position, WP overestimated LAP (13.3 +/- 3.4 vs. 8.0 +/- 2 mm Hg; p less than .01) at 20 cm H2O of PEEP, whereas CVP (8.8 +/- 2.1 mm Hg) closely reflected LAP. Thus, by placing the catheter tip vertically below the left atrium in supinely and laterally positioned patients, CVP and WP both produced reliable estimates of LAP despite an acute increase in alveolar pressure. When the pulmonary artery catheter tip was vertically above the left atrium, WP overestimated LAP. Under these conditions, CVP remained a reliable estimate of LAP. We conclude that CVP measurement as an estimate of LAP in this patient population could be used and not ignored. This is true in patients with previously documented good LAP-CVP correlation who are subjected subsequently to conditions which may produce an LAP-WP discrepancy (high PEEP and catheter tip malposition).