Computerized tomography of the lungs and arterial oxygen tension studies during apnoea in anaesthetized young lambs

Computerized tomography (CT) of the lungs and arterial oxygen tension studies were performed during general anaesthesia in an animal model to understand changes in pulmonary atelectasis associated with anaesthesia in children during a 2 min apnoeic period. Six anaesthetized lambs were subjected to three periods of apnoea lasting 2 min each. A series of 10 mm CT transaxial views were taken at three levels of the chest and arterial blood gases were analysed at the start of the apnoeic period (baseline) and again every 30 s during the apnoeic period. The areas of atelectasis were measured using the extended Hounsfield scale. The results confirmed that significant background atelectasis was associated with general anaesthesia as found in adult human studies, but failed to demonstrate any increase in atelectasis during the period of induced apnoea. The decline in arterial oxygen tension in this study could be explained due to simple utilization of oxygen in keeping with physiological principles.