Schematic relation between Pao2 and cardiac output during one-lung ventilation (OLV). As cardiac output decreases below baseline, arteriovenous shunt (s/t) decreases, but the mixed venous oxygen saturation() also decreases resulting in a net decrease in Pao2. Conversely, raising cardiac output above baseline tends to increase not only but also s/t, and the net result again is a decrease in Pao2. Pao2 = arterial oxygen tension. (Based on data from references 100 and 101.)