Ventilatory responses of children to changes in deadspace volume. Studies using the T-piece (Mapleson F) system

Twelve patients (4.3-25.3 kg) undergoing minor surgical procedures were investigated during halothane anaesthesia with spontaneous breathing through a modified T-piece (Mapleson F) with an apparatus deadspace that could be changed from 2 ml (VDsmall) to 16 ml (VDlarge). Immediately following the switch from VDsmall to Vlarge ETCO2 (mean +/- 1 SD) increased from 6.89 +/- 1.09% to 7.61 +/- 1.14% (ns) then gradually decreased during a 10-min period. The initial plateau of FlCO2 (mean +/- 1 SD) with VDlarge was 0.74 +/- 0.34%, but gradually decreased to 0.63 +/- 0.25% after 10 min. This was achieved by an increase in VE (P less than 0.05 by 2 min). After 10 min VE had increased by more than 40% (P less than 0.01) as a result of an increase in VT (mean +/- 1 SD) of 14.6 +/- 6.5 ml. After 10 min of VDlarge ventilation, VA and VCO2 were maintained at VDsmall values. The adequate ventilatory response to the large deadspace was seen in all patients, but the ventilatory efficiency, as judged by VD/VT and VENCO2 ratios, was reduced significantly in the children weighing less than 10 kg.