Effect of lung zones on pulmonary artery catheter monitoring

The lung can be divided into three physiologic zones, based on the relationship of alveolar pressure (P_A), mean pulmonary artery pressure (P_a), and pulmonary capillary wedge pressure (P_c). Pulmonary capillary wedge pressure approximates left atrial pressure (P_LA) under zone three conditions, when vascular pressures exceed alveolar pressure. If the pulmonary artery catheter is wedged under non-zone three conditions, alveolar pressure swings interfere with accurate assessment of pulmonary capillary wedge pressure.