The efficiency of various humidifiers for respired gas

Eight different breathing gas humidifiers were tested by humidity measurements using two independent methods under simulated clinical conditions. The comparison considering the influence of tidal volume and inspiratory/expiratory ratios revealed great differences between the individual devices depending on the kind of humidification and functional principles. Only four of the humidifiers tested: Ultrasonic Nebulizer NB 108, Hydrotrop 200, Bennett Cascade and Nicholas Humidifier, gave a constant performance of more than 30.75 g H2O/m3 absolute humidity or 70% relative humidity, related to 37 degrees C. However, humidification and heating of the inspired gas could be ensured only by the last three devices. The humidifiers Bird 500 cm3 Micronebulizer, Ultrasonic Nebulizer NB 100 and Draeger Compressor 660, were strongly dependent on the respiration parameters and exceeded the required minimum of 70% relative humidity only under certain conditions. The Engstroem ER-200 Vaporizer had a low performance and was not suitable as a breathing gas humidifier for longterm ventilation.