Figure 49-29 Listing of many of the components of the anesthetic experience that might determine the amount of regional hypoxic pulmonary vasoconstriction. The clockwise numbering of considerations corresponds to the order in which these considerations are discussed in the text. FIO₂ , inspired oxygen fraction; OaCO₂ , alveolar carbon dioxide tension; PEEP, positive end-expiratory pressure; Pv̄O₂ , mixed venous oxygen tension; PVP, pulmonary vascular pressure; V̇/, ventilation-perfusion ratio. (From Benumof JL: Anesthesia for Thoracic Surgery. Philadelphia, WB Saunders, 1987.)