The Effect Of Supplemental Nitrous Oxide On Inspired Concentration Of Sevoflurane

ObjectiveTo investigate the influrence of nitrous oxide(N₂O) inhalation on the inspired concentration of sevoflurane.MethodsForty children scheduled for selective paediatric orthopaedic surgery under general anesthesia.We used controlled trial,successively children in groupâ… inhaled sevoflurane in O₂ for anesthesia maintenance,and groupâ…¡inhaled sevoflurane with 50%N₂O and 50%O₂.Anesthesia was induced with fentanyl 2μg/kg,propofol 2.5mg/kg and succinylcholine 1.5mg/kg intravenously.After endotracheal intubation, all children were ventilated with PETCO₂ between 35～40 mmHg.In groupâ… the fresh gas flow was 2 L/min of O₂,and in groupâ…¡the fresh gas flow was 1 L/min of O₂ with 1 L/min of N₂O.The sevoflurane vaporizer was kept at 2%.The concentrations of sevoflurane in inspired gas were measured at 0,1,2,3min of sevoflurane inhalation. The MAP,HR,SpO₂ and PETCO₂ were also recorded at the same time points.Result(1) The inspired concentrations of sevoflurane in groupâ… were higher than those in groupâ…¡(P＜0.01).(2) The time of achieving the goal concentration in groupâ… were shorter than those in groupâ…¡(P＜0.01).ConclusionThe establishment of sevoflurane concentration was slowed in the inhaled anesthesia when N₂O was added in the fresh gas of oxygen because N₂O decreased the outflow concentration of sevoflurane vaporizer.