Changes in ventilatory patterns during halothane anaesthesia in children.

Changes in ventilatory variables (VE, VE, f, Tl/Ttot, VT/Tl, PE'CO2) were studied in 12 unpremedicated children, weighing between 10 and 20 kg, during halothane anaesthesia. At an inspired concentration of 0.5% halothane, respiratory rate increased, VT decreased, and VE did not change markedly. When the inspired halothane concentration increased further, there was a significant decrease in VE, mainly as a result of a marked decrease in VT. PE'CO2 increased significantly and inspiratory duty cycle decreased at high inspired halothane concentrations. On return to baseline (0.5% halothane), there was a significant decrease in inspiratory timing and a significant increase in PE'CO2. The relations between these changes and the effect of halothane on inspiratory muscles are discussed.