Devices used to humidify respired gases.

The efficiency of HMEs decreases with increasing tidal volumes. HMEs always result in an elevation of the inspiratory and expiratory airway resistances; this should be considered especially in cases that involve spontaneous respiration. The pressure drop across HMEs should be less than 2 hPa for a flow of 60 L/min, a level that also has been measured for cascade humidifiers.

Evaluation of heated humidifiers for use on intubated patients: a comparative study of humidifying efficiency, flow resistance, and alarm functions using a lung model.

Objective: Evaluation of humidification efficiency, flow resistance, and alarm functions of heated humidifiers (HH;(Kendall-Aerodyne-delta, Fisher&Paykel-MR 730; Dräger-Aquapor; Puritan-Bennett-Cascade II) in accordance with ISO/EN-8185:1997 and on a ventilated lung model in accordance with ISO/EN-9360:2000.

Methods: Humidification efficiency was evaluated by (a) measuring the water content of the inspiratory air on perfusion with different gas flows, (b) measuring the water loss of a lung model, and (c) simultaneous measurement of the in- and expiratory water content with a capacitive hybrid sensor. The resistance characteristics were measured, the data were compared with a mathematical approximation.