Wedge pressure confirmation by aspiration of pulmonary capillary blood

In order to define the contribution of wedge blood composition to pulmonary artery wedge pressure (WP) measurement, we made 28 comparisons of WP and left atrial pressure (LAP) in 16 stable patients with pulmonary or cardiac failure after cardiac surgery. All technical problems associated with initial WP measurements were eliminated before simultaneously recording WP and LAP. Wedge blood samples (w), withdrawn from the distal pulmonary artery catheter port in the balloon occlusion position, were compared with paired arterial (a) blood samples. Wedge blood was defined as pulmonary capillary blood when the following three wedge-arterial gradient criteria were satisfied: (PwO2 - PaO2) greater than or equal to 19 torr; (PaCO2 - PwCO2) greater than or equal to 11 torr; and (pHw-pHa) greater than or equal to 0.08. When capillary blood was withdrawn from the wedge position, there was no difference between WP and LAP measurements. When wedge blood failed to satisfy capillary criteria, WP was significantly (p less than .05) different from LAP. Aspiration of capillary blood from the wedge position in ICU patients confirms that WP faithfully reflects LAP. It identifies those differences between WP and LAP which remain after technical problems are eliminated.