General anesthesia and the lung.

In this review, an attempt has been made to select, evaluate, and interpret the pertinent literature relative to general anesthesia and the lung. Concepts of intrapulmonary gas exchange and respiratory system mechanics were synthesized, emphasizing the importance of changes in intrapulmonary gas distribution that are induced by general anesthesia and exploring the possible underlying mechanisms of these changes. The area of control mechanisms and the effects of anesthesia on respiratory regulation were not discussed, nor was the distribution of pulmonary blood flow examined. The following general conclusions can be reached: (1) impaired gas exchange occurs during general anesthesia, with both impaired oxygenation and CO2 elimination; (2) increased venous admixture and increased alveolar dead space impair gas exchange; (3) the distribution of ventilation is changed during general anesthesia, and this change is related to a decrease in FRC in the recumbent positions and to altered chest-wall mechanics. Numerous questions regarding the effect of anesthesia on the lung remain unanswered. The close relationship between advances in pulmonary physiology and the pulmonary effects of anesthetic actions is increasingly apparent, as is the importance of this knowledge in applying mechanical ventilation and end-expiratory pressure to patients with pulmonary disease.