The effect of two types of humidifying devices on humidity of inspired gas and tidal volume by ventilator monitoring

BACKGROUND: In general anesthesia, a heat and moisture exchanger (HME) is used to prevent hypothermia and to maintain humidity of inspired gas. We hypothesized that after using a HME expiratory tidal volume decreases because a HME traps the expired vapor.The aim of this study was to evaluate the humidity of expired gas and to investigate the accuracy of tidal volume monitoring. METHODS: Forty patients undergoing elective surgery under general anesthesia were randomly allocated into two groups.Group P (n = 20) used Pall Breathing filter (pall BB25, ACE medical, Korea) and Group H (n = 20) used Hygrobac S (Mallinckrodt Dar, Mirandola, Italy) between endotracheal tube and Y-piece.And with same kind of ventilator, we measured expiratory tidal volume, temperature and relative humidity at before and after HEM.And we recorded expiratory tidal volume monitored by ventilator with and without HME. RESULTS: The relative humidity was significantly higher at before using HEM than after using HEM in both group.The temperature in Group H was higher when measured at before HME but not in Group P.The measured expiratory tidal volume at before and after HEM was not significantly different. The tidal volume monitored by ventilator with HEM was significantly smaller than without HEM, by 3.1% in Group P and 5.3% in Group H. CONCLUSIONS: The HMEs improve inspiratory humidity and temperature of anesthetic gas.But monitored expiratory tidal volume was underestimated when using HMEs.

Influence of Heat and Moisture Exchanger Filter on Temperature of Inspiratory and Endotracheal Gas / 医疗卫生装备

Objective To investigate the influence of heat and moisture exchanger filter(HMEF)on the temperature of inhaled and endotracheal gas during mechanical ventilation. Methods Thirty patients (ASAI-II) were selected and divided randomly into 2 groups: control group and HMEF group. The temperature of inhaled gas was monitored with hygrothermograph and the temperature of endotracheal gas was monitored with temperature probe. Baseline values were set at the moment of intubation and then the values were recorded at the first hour after intubation and the second hour after intubation. Results With the increase of the mechanical ventilation time, the temperature of inhaled and endotracheal gas decreased significantly in control group and increased significantly in HMEF group; The temperature of both inhaled and endotracheal gas in HMEF group were significantly higher than that in control group at the moment of the first hour after intuba- tion and the second hour after intubation; There was correlation between the temperature of inhaled gas and the temperature of endotracheal gas at the moment of intubation, but it was not the same at the moment of the first hour after intubation or the second hour after intubation. Conclusion HMEF can make the cold inhaled gas warmer when it reached the trachea; Temperature probe may be better than hygrothermograph for monitoring the temperature of trachea.