Fig. 4. The changes in arterial oxygen partial pressure (Pao2) and in the gradient between the lower inflection point of the static lung inflation compliance curve (IP) and the plateau end-expiratory pressure (EEP) associated with the application of 5 cm H2O positive end-expiratory pressure during one-lung ventilation in 42 patients. There was a significant inverse correlation (r = 0.76, P < 0.001). In the patients (n = 6) in whom positive end-expiratory pressure had the most effect to move the EEP closer to the IP, the Pao2improved. In the majority of patients, positive end-expiratory pressure caused no change or increased the IP-EEP gradient, and Pao2either did not change or decreased.