Figure 49-11 Distribution of ventilation in a patient in the lateral decubitus position when awake (A) and when anesthetized (B). Induction of anesthesia has caused loss of lung volume in both lungs, with the nondependent lung moving from a flat, noncompliant portion to a steep, compliant portion of the pressure-volume curve and the dependent lung moving from a steep, compliant part to a flat, noncompliant part of the pressure-volume curve. Thus, an anesthetized patient in a lateral decubitus position has more of the tidal ventilation in the nondependent lung (where perfusion is the least) and less of the tidal ventilation in the dependent lung (where perfusion is the greatest). P, transpulmonary pressure; V, alveolar volume. (From Benumof JL: Anesthesia for Thoracic Surgery. Philadelphia, WB Saunders, 1987.)