Figure 49-12 Schematic depiction of a patient in the lateral decubitus position in which the closed-chest anesthetized condition is compared with the open-chest anesthetized and paralyzed condition. Opening the chest increases nondependent lung compliance and reinforces or maintains the larger part of tidal ventilation going to the nondependent lung. Paralysis also reinforces or maintains the larger part of tidal ventilation going to the nondependent lung because the pressure of the abdominal contents (P_AB ) pressing against the upper part of the diaphragm is minimal (smaller arrow), and it is therefore easier for positive-pressure ventilation to displace this lesser resisting dome of the diaphragm. P, transpulmonary pressure; V, alveolar volume. (From Benumof JL: Anesthesia for Thoracic Surgery. Philadelphia, WB Saunders, 1987.)