Variable apparatus deadspace

A variable apparatus deadspace was used to maintain normocapnia during artificial ventilation of the lungs in anaesthetised adults. End-tidal carbon dioxide tension could be varied, if the need arose, within the range 4.0-5.2 kPa in both open and circle breathing systems when a fixed tidal volume of 12 ml.kg-1 and minute volume ventilation of 120 ml.kg-1.min-1 were employed.