Pulmonary ventilation and gas exchange in children anaesthetized with halothane, enflurane and isoflurane.

The effects of similar anaesthetic levels of halothane (1.3 MAC), enflurane (1.2 MAC) and isoflurane (1.1 MAC) on pulmonary ventilation and gas exchange were investigated in 24 children subjected to minor and intermediate paediatric surgical procedures. Eight children were anaesthetized with each agent, pneumotachography and capnography were used, and airway as well as oesophageal pressures were measured. Minute ventilation (VE) was lower with enflurane than with halothane (P less than 0.001) and isoflurane (ns). Tidal volumes were, however, similar and variations in VE were thus caused by lower respiratory rates with enflurane than with the two other agents. Alveolar ventilation (VABohr) and carbon dioxide elimination (VCO2) were smaller and end-tidal CO2 tension higher with enflurane. Ventilatory efficiency was, however, somewhat better with enflurane as indicated by lower VDBohr/VT (ns) and VE/VCO2 (P less than 0.05) ratios compared with the two other agents. The effects of all three agents on dynamic compliance were similar, while total pulmonary resistance was less with isoflurane than with halothane and enflurane. It is concluded that although minute ventilation was smaller with enflurane than with halothane and isoflurane, ventilatory efficiency was similar due to a smaller dead space ventilation as a result of the lower respiratory rates in children anaesthetized with enflurane.