Oxygen in nitrogen versus nitrous oxide during pediatric general anesthesia

Induction of anesthesia decreases lung volumes, giving areas of non-ventilated lung. Nitrogen is a slowly-absorbed gas that could prevent resorption of gases from these closed spaces, preventing atelectasis and improving oxygen saturations during recovery.

We evaluated oxygen saturations during emergence after intra-operative administration of 33% oxygen in nitrogen versus 33% oxygen in nitrous oxide in 62 children having elective urologic surgery. Patients were randomly assigned to either group A (2.5 L/min air with 0.5 L/min oxygen) or group N (2 L/min nitrous oxide and 1 L/min oxygen). Flowmeters were covered to maintain blinding. Anesthetic technique was standardized (laryngeal mask airway, caudal, halothane, and deep extubation). Patients breathed room air during emergence, while a blinded observer recorded duration of desaturations by stopwatch for 15 min.

We found similar desaturations in both groups. The difference in desaturations < 94% at an interim 2-min total probably reflects diffusion hypoxia and was not significant at 15 min. The frequency of desaturations < 87% during emergence was significantly greater in children who were crying during induction.

The intra-operative use of air versus nitrous oxide has no substantial effect on oxygen saturations during emergence from anesthesia in children. These results are consistent with a recently published mathematical model.