Ventilatory Responses of Children to Changes in Deadspace Volume

Alveolar deadspace is greater during anaesthesia than in the conscious state (Nunn and Hill, 1960), and during spontaneous ventilation it increases with depth of anaesthesia (Kain, Panday and Nunn, 1969). However, although the additional influence of apparatus deadspace was investigated by Kain, Panday and Nunn (1969), few studies have considered the effects of apparatus deadspace on anaesthetized children, although these are relatively more important in smaller patients. In one study in children anaesthetized with halothane (Lindahl, Hulse and Hatch, 1984), smaller children were shown to have a higher percentage deadspace ventilation as a result of their higher respiratory rates and of a higher total deadspace to tidal volume ratio, while net deadspace (apparatus deadspace excluded) to tidal volume ratio did not differ with rate. In this study, the ventilatory responses to two different apparatus deadspaces (2 and 16 ml) were compared in spontaneously breathing children during halothane anaesthesia, and the efficiency of ventilation in younger and older children evaluated.