Improving Oxygenation during One-lung Ventilation in Dogs

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Abstract
During 1-lung ventilation in dogs, the individual and combined effects of 5, 10 and 15 cm H2O of O2 PEEP [positive end expiratory pressure] to the nonventilated lung and nonocclusive inflation of a pulmonary artery catheter balloon (PAB) in the main pulmonary artery of the nonventilated lung on PaO2, .ovrhdot.Qs/.ovrhdot.Qt and blood flow to the nonventilated lung (.ovrhdot.Qtest/.ovrhdot.Qt) were studied. Periods of 1-lung ventilation alone resulted in PaO2 of 61 .+-. 5 torr (mean .+-. SE), .ovrhdot.Qs/.ovrhdot.Qt of 50 .+-. 3% and .ovrhdot.Qtest/.ovrhdot.Qt of 41 .+-. 6%. Five and 10 cm H2O of O2 PEEP caused a greatly decreased .ovrhdot.Qs/.ovrhdot.Qt (22 .+-. 4 and 21 .+-. 4%, respectively) and increased PaO2 (327 .+-. 43 and 330 .+-. 40 torr, respectively) while .ovrhdot.Qtest/.ovrhdot.Qt remained unchanged; 15 cm H2O of O2 PEEP caused similar PaO2 and .ovrhdot.Qs/.ovrhdot.Qt changes while .ovrhdot.Qtest/.ovrhdot.Qt significantly decreased (to 19 .+-. 6). Nonocclusive inflation of the PAB alone caused moderate favorable changes in PaO2 and .ovrhdot.Qs/.ovrhdot.Qt (but less than those caused by any level of O2 PEEP) which were due to a decreased .ovrhdot.Qtest/.ovrhdot.Qt (to 22 .+-. 5%). Inflation of the PAB during any level of O2 PEEP did not change PaO2 or .ovrhdot.Qs/.ovrhdot.Qt significantly but still decreased .ovrhdot.Qtest/.ovrhdot.Qt significantly. Probable mechanisms of efficacy of nonventilated lung manipulations are as follows: low levels of O2 PEEP maintain the patency of airways, allowing nonventilated lung alveoli to participate in gas exchange; high levels of O2 PEEP act by this mechanism as well as by causing blood flow diversion to the ventilated lung; PAB inflation acts by blood flow diversion to the ventilated lung alone. Low levels of O2 PEEP to the nonventilated lung should be used when possible if hypoxemia occurs during 1-lung ventilation. Flow diversion caused by PAB inflation may be uniquely useful in situations in which O2 PEEP to the nonventilted lung is impractical (e.g., surgical interference, pulmonary hemorrhage) or impossible (e.g., pulmonary lavage).