Effect of positive end-expiratory pressure (PEEP) on pulmonary hemodynamics

Pressure tracings from the same patient recorded at different levels of positive end-expiratory pressure (PEEP). The top panel shows 0 PEEP, the middle panel PEEP = 15 cm H₂O, and the bottom panel PEEP = 20 cm H₂O. Pulmonary artery pressure (P_pa) is shown at the left of the tracing. The right side of the tracing shows wedge (pulmonary artery occlusion) pressure (P_paO). The red bars indicate the degree of respiratory (or respirophasic) variation (I, E) exhibited at each level of PEEP in pulmonary artery pressure and wedge pressure. The ratio of respiratory variation in pulmonary artery pressure divided by respiratory variation in the wedge pressure was close to 1 when PEEP = 0 or 15 cm H₂O PEEP. This increased to 2.3 at a level of 20 cm H₂O PEEP. This suggests a shift from zone three to a non-zone three condition, where airway pressure has exceeded intravascular pressure at the balloon occluded pulmonary artery catheter tip. The end-expiratory wedge pressure value during PEEP = 20 cm H₂O is markedly higher than during PEEP = 15 cm H₂O (18 versus 10 mmHg), a change that cannot solely be explained by the increase in PEEP.