Figure 17-33 Anesthesia and surgery may cause a progressive cephalad displacement of the diaphragm. The sequence of events involves assumption of the supine position, induction of anesthesia, establishment of paralysis, assumption of several surgical positions, and displacement by retractors and packs. Cephalad displacement of the diaphragm results in decreased functional residual capacity (↓ FRC). Pab, pressure of abdominal contents. (Redrawn with modification from Benumof JL: Anesthesia for Thoracic Surgery, 2nd ed. Philadelphia, WB Saunders, 1995, Chapter 8.)