Optimization of Arterial Oxygenation during One-Lung Anesthesia

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Abstract
The effects of different respiratory maneuvers on PaO2 [arterial O2 partial pressure], .ovrhdot.Qs/.ovrhdot.Qt [amount of blood shunted through the lungs] and cardiac output were studied during 1-lung anesthesia in 21 adult patients, who were undergoing pulmonary surgery in lateral position with halothane-O2 anesthesia using endobronchial intubation. The patients were divided into 3 groups. In group A (n = 11) 7 different respiratory maneuvers were sequentially performed. When both lungs were ventilated (maneuver A), PaO2 and .ovrhdot.Qs/.ovrhdot.Qt were 376 .+-. 28 torr (mean .+-. SE) and 26 .+-. 2.33% (mean .+-. SE), respectively. Corresponding values were 155 .+-. 25 torr and 38 .+-. 1.5% when the upper lung was deflated (maneuver B), and 85 .+-. 11 torr and 44 .+-. 4% when PEEP [positive-end expiratory pressure] (10 cm H2O) was added to the dependent lung, with the upper lung remaining deflated (maneuver C). When the collapsed upper lung was insufflated with O2 (7 l/min) with the lower lung receiving PEEP (maneuver D), PaO2 and .ovrhdot.Qs/.ovrhdot.Qt were 127 .+-. 29 torr and 38 .+-. 3%, respectively; 177 .+-. 34 torr and 37 .+-. 3.5% when the upper lung was insufflated with O2 and the lower lung ventilated without end-expiratory pressure (maneuver E). When the upper lung was insufflated with O2 at 10 cm H2O pressure with the dependent lung ventilated with PEEP (maneuver F), PaO2 was 248 .+-. 41 torr and .ovrhdot.Qs/.ovrhdot.Qt was 31 .+-. 2%; finally, during insufflation of the upper lung at 10 cm H2O pressure, while the lower lung was ventilated with zero end-expiratory pressure (maneuver G), PaO2 averaged 286 .+-. 49 torr and .ovrhdot.Qs/.ovrhdot.Qt 28 .+-. 2.5%. Cardiac output was reduced only when the dependent lung was ventilated with PEEP and the deflated upper lung insufflated with O2 with or without pressure. In group B (n = 5) the effects of only maneuver F on arterial oxygenation were evaluated 50, 95 and 140 min after the start of anesthesia. In group C (n = 5), only maneuver G was studied 50, 95 and 140 min after the start of anesthesia. The values for PaO2 and .ovrhdot.Qs/.ovrhdot.Qt did not differ from each other at these time intervals, and were comparable with the values obtained during corresponding maneuvers in group A patients. Arterial oxygenation can be optimized during 1-lung anesthesia by O2 insufflation of the upper deflated lung at 10 cm H2O pressure, while the lower lung is ventilated with zero end-expiratory pressure.

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