Lung aeration. The effect of pre-oxygenation and hyperoxygenation during total intravenous anaesthesia

We have investigated the effect of pre-oxygenation and hyperoxygenation (an increase in inspired oxygen fraction from 0.4 to 1.0 after induction of general anaesthesia) on aeration and atelectasis formation in the lungs during total intravenous anaesthesia. Twenty-seven consecutive patients were randomly allocated to group 1 (with pre-oxygenation), group 2 (without pre-oxygenation), or group 3 (hyperoxygenation). Lung aeration was investigated by means of spiral computed tomography. The aeration of lung regions identified by computed tomography scans was divided into five categories: over-aeration, normal aeration, reduced aeration, poor aeration, and atelectasis formation. In group 1 larger areas of atelectasis were found in the basal parts of the lungs compared to group 2. In group 3 a significant increase in atelectatic areas with a corresponding reduction in areas with reduced aeration occurred at the bases of the lungs. The considerable increase in atelectasis associated with pre-oxygenation and its rapid appearance during hyperoxygenation suggest that these procedures should be used with caution.