N2O-free low-flow anesthesia technique for children

Abstract

Background: The use of N2O during low-flow anesthesia (LFA) causes difficulty in predicting inspired gas mixtures and oxygen concentration due to accumulation. An alternative technique, which uses a mixture of oxygen and air and a morphine infusion to replace N2O, has been evaluated in children during LFA, and the clinical effects and composition of gases in the system are presented here. Methods: Thirty-five children aged 2-13 years undergoing major urogenital surgery were recruited into the study. Following a standardized induction, anesthesia was maintained with 2% sevoflurane in combination with a morphine infusion. After induction with 4 1 min-1, flow rates were reduced to 2 1 min-1 and finally to 1 1 min -1 at 10 min (0.5 1 oxygen + 0.5 1 air). The delivered oxygen concentration, oxygen saturation and the inspired and expired O2, sevoflurane and CO2 concentrations were recorded from the start of induction to the end of anesthesia. Results: The duration of LFA was 132±89 min. The concentration of oxygen delivered by the flow meters during this period was 55-60%. Although the changes in inspired and expired oxygen and sevoflurane and inspired CO2 related to the duration of LFA were statistically significant (P < 0.0001), they were not clinically relevant. All vital parameters were stable. Four patients required supplemental morphine and nine presented emergence agitation. Conclusion: We concluded that an N2O-free LEA technique with 0.5 1 min-1 of air and 0.5 1 min-1 of O2 supplemented by sevoflurane and a morphine infusion is safe and effective in children. The resulting high-inspired oxygen concentration prevents occurrence of hypoxic gas mixtures, and the use of supplemental morphine compensates for the absence of N2O and overcomes the possibility of light anesthesia arising from a decrease in the inspired sevoflurane concentration. © Acta Anaesthesiologica Scandinavica (2005).