Figure 17-34 An anesthetized patient in the supine position has increased airway resistance as a result of decreased functional residual capacity (FRC), decreased caliber of the airways, endotracheal intubation, and connection of the endotracheal tube (ET) to the external breathing apparatus and circuitry. (Redrawn with modification from Benumof JL: Anesthesia for Thoracic Surgery, 2nd ed. Philadelphia, WB Saunders, 1995, Chapter 8.)