Humidification during low-flow anesthesia in children.

Purpose: The aim of this study was to compare the effect of low-flow anesthesia with or without a heat and moisture exchanger with high-flow anesthesia on airway gas humidification in children.

Methods: One hundred twenty children were randomly assigned to one of three groups: low-flow anesthesia with 0.5l·min of total gas flow (LFA,n=40), low-flow anesthesia with 0.5l·min using a heat and moisture exchanger (HME,n=40), and high-flow anesthesia with 6l·min (HFA,n=40). The temperature and relative humidity of the inspired gas were measured throughout anesthesia.

Results: The relative humidity of the inspired gas in the HME group was increased compared with that of the LFA and HFA groups 20 min after induction (p<0.05). The airway humidification in the LFA group was higher than that in the HFA group 10 min after induction (p<0.05). The temperature of the inspired gas in the HME group was increased compared with that in the LFA and HFA groups after 70 min (P<0.05).

Conclusion: Low-flow anesthesia is less effective in providing adequate humidification of inspired gas than low-flow anesthesia with a heat and moisture exchanger, but significantly better than high-flow anesthesia in children.