Pulmonary shunting during anaesthesia in man

{Mathematical expression} was determined during halothane and oxygen anaesthesia in 22 patients. All were believed to have no pulmonary dysfunction. A surgical operation was in progress and respiration was controlled. {Mathematical expression} was minimal in 15 of these patients (mean 3.9 ± 0.3 per cent), indicating that anaesthesia and operation can be conducted in man without a significant increase of pulmonary shunting. The level of shunting was increased in the other seven patients. In neither group was {Mathematical expression} altered by the passage of time. Age varied between 23 and 61 years and was directly and significantly correlated to {Mathematical expression} (r = 0.57, P < 0.01).