Heat and moisture exchangers (HME) are often used to maintain humidity of breathing circuits during anesthesia. It is also known to increase dead space ventilation in respiratory distress syndromes. However, the effect of a pediatric HME in healthy pediatric patients has not yet been clarified. The purpose of this study was to evaluate the effect of a pediatric HME on dead space in healthy pediatric patients during anesthesia.

20 ASA physical class I pediatric patients, without respiratory impairment, who underwent elective surgery for inguinal hernia or hydrocele with general anesthesia were enrolled. Fifteen minutes after ventilation with and without pediatric HME (internal volume of 22 ml), hemodynamic variables, end tidal CO₂, minute volume and airway pressure were measured, and arterial blood sampling was conducted simultaneously.

The removal of pediatric HME decreased PaCO₂ significantly from 46.1 ± 6.9 mmHg to 37.9 ± 4.3 mmHg (P < 0.001) and increased the pH from 7.32 to 7.37 (P < 0.001). The differences between PaCO₂ with and without HME (Δ PaCO₂) were significantly correlated with weight (P < 0.001, β1 = -0.749) and age (P = 0.002, β1 = -0.623).

The use of a pediatric HME significantly increased PaCO₂ in healthy pediatric patients that was inversely proportional to weight and age. The use of pediatric HME should be carefully considered in small pediatric patients.