Paediatric HME-filter

Heat-and-moisture exchangers (HME) are the most commonly used humidi-filters. HME have a low resistance to airway flow and a relatively small volume (about 75 ml), which is not too large to impair ventilation of healthy adult patients ventilated with a tidal volume of 8-12 ml/kg [1,2]. Therefore, most studies to evaluate the dead space effect of HME in adult patients have been conducted in ICU patients receiving lung protective ventilation with a lower tidal volume of 4-6 ml/kg [1,3].

However, with the exception of extremely small premature neonates, most pediatric patients undergoing general anesthesia are applied with only one size of pediatric HME between the tracheal adaptor and the Y piece. The volume of a pediatric HME is generally 20-25 ml, which is about 1/10 of the tidal volume of a 20 kg patient or 1/5 for a 10 kg patient. Even when used in patients that are healthy without acute lung disease, smaller pediatric patients would be affected by the use of a pediatric HME.

One previous study was conducted to evaluate the effect of humidi-filters on dead space in pediatric patients [5]. However, that study examined how much more ventilation and breathing work were required to maintain the same end-tidal concentration of CO2 (EtCO2), but not the PaCO2, in pediatric patients under 2 years old. However, when there was a big dead space ventilation, the EtCO2 could not be representative of PaCO2 and the ages of the study population were limited to under 2 years.

Therefore, in this study, we examined whether the PaCO2 of healthy pediatric patients (1-96 months) was significantly influenced by the use of pediatric HME. Moreover, we investigated the correlation between the effect of pediatric HME on CO2 elimination and demographic variables.