Changes in respiratory physiology during ether--air anaesthesia.

Measurements of arterial oxygen and carbon dioxide tension, alveolar ventilation, alveolar to arterial oxygen difference, and ratio of deadspace to tidal volume have been made to show the changes induced by ether/air anaesthesia with spontaneous respiration, with mechanical ventilation, and with mechanical overventilation. There was a disproportionate fall in oxygen tension during spontaneous respiration widi ether/air anaesthesia, and an increased alveolar to arterial oxygen tension difference. The latter was still further increased by both "normal" ventilation and over ventilation. Alveolar ventilation was at all times adequate for the elimination of carbon dioxide. The ratio of the physiological deadspace to the tidal volume was increased during anaesthesia only when artificial ventilation was used. The possible causes of these findings are discussed together with their implications for the use of ether/air anaesthesia.