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Ventilatory CO2 response, respiratory drive and timing in children anaesthetized with halothane, enflurane or isoflurane.

Ventilatory CO2 response, respiratory drive and timing were investigated during anaesthesia prior to surgery in 24 spontaneously breathing cardiopulmonary healthy children. Anaesthesia was maintained with halothane, enflurane or isoflurane combined with oxygen-nitrous oxide (FIO2 0.5). The MAC values were 0.97 for halothane, 0.92 for enflurane and 0.92 for isoflurane. Pneumotachography and capnography were used and airway pressures were measured before and during breathing of 4% CO2 as well as during airway occlusion. Changes in minute ventilation were less with enflurane than with halothane and isoflurane in response to 4% CO2; however, tidal volumes were equally increased with all three agents. End-tidal CO2 tensions were significantly higher during enflurane than during both halothane and isoflurane anaesthesia, before as well as during CO2 stimulation. Respiratory rates were lower in children anaesthetized with enflurane and were unresponsive to CO2 when all three volatile agents were used. During CO2 challenge, mean inspiratory flow and maximal occlusion pressure were similarly increased in all groups.