Evaluation of the efficiency of heat and moisture exchangers during paediatric anaesthesia.

This study evaluates the efficiency of heat and moisture exchangers (HMEs) in allowing adequate humidification and warming during anaesthesia in children. Eighteen paediatric patients undergoing anaesthesia were divided into two groups: group A ten patients: infants up to 10 kg-->Hygrobaby HME; group B 8 patients: children above 10 kg-->Hygroboy HME. The following parameters were evaluated: body temperature (bT), room temperature (rT), fresh gas temperature, HME warm-up time, inspired and expired gases temperature and humidity, conserving efficiency, and duration of anaesthesia. Gas temperatures were recorded by means of a recorder fitted with four thermal probes. Humidity values were mathematically derived. The correlation between efficiency and rT, bT, and fresh gas temperature was computed. In both groups the inspired gases temperatures were below 30 degrees C. Inspired absolute humidity was never more than 28 mgH2O.l(-1). The conserving efficiency was good (0.93 in both groups). A positive correlation was found between efficiency and fresh gas temperature. HMEs did not meet the minimum standards for humidity and heating during anaesthesia in children, although their conserving efficiency was found to be satisfactory.