Figure 49-7 Effect of 1 minimum alveolar concentration (MAC) isoflurane anesthesia on shunt during one-lung ventilation (1LV) of normal lungs. This diagram shows that for two-lung ventilation, the ratio of the percentages of blood flow to the nondependent and dependent lungs is 40:60 (left-hand side). When two-lung ventilation is converted to one-lung ventilation (as indicated by atelectasis of the nondependent lung), the hypoxic pulmonary vasoconstriction (HPV) response decreases blood flow to the nondependent lung by 50%, so the nondependent-dependent lung blood flow ratio is now 20:80 (middle). According to the data of Domino and colleagues,^[186] administration of 1 MAC isoflurane anesthesia should cause a 21% decrease in the HPV response, which would decrease the blood flow reduction from 50% to 40%. Consequently, the nondependent-dependent lung blood flow ratio would now become 24:76, which represents a 4% increase in total shunt across the lungs (right-hand side). (From Benumof JL: Isoflurane anesthesia and arterial oxygenation during one-lung ventilation. Anesthesiology 64:419, 1986.)