N2O-free low-flow anesthesia technique for children

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.

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 l min(-1), flow rates were reduced to 2 l min(-1) and finally to 1 l min(-1) at 10 min (0.5 l oxygen + 0.5 l 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.

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.

We concluded that an N2O-free LFA technique with 0.5 l min(-1) of air and 0.5 l 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.