Moisture‐conserving efficiency of condenser humidifiers*

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Abstract
The moisture-conserving efficiency of commercially available condenser humidifiers (small, disposable, airway humidifiers) was studied. A comprehensive comparison of all currently available condenser humidifiers utilising a laboratory system which simulated a breathing, intubated patient in temperature, humidity, dead space, and respiratory pattern characteristics was undertaken. The percentage of moisture conserved, or efficiency, of the humidifiers was calculated gravimetrically from the water loss of the testing system with and without the condenser humidifiers. The Portex Humid-Vent and Trach-Vent, Siemens Servo 150 and the Terumo Brethaia were evaluated. The data revealed an inverse correlation between efficiency and tidal volume. The most efficient were the Portex Humid-Vent at low tidal volumes and Siemens Servo 150 at the mid and high tidal volumes. To achieve a minimum inspired water content of 33 mg H2O/litre gas, a 79% condenser humidifier efficiency is necessary. None of these units met this requirement; however, they may be appropriate for limited clinical application.