• M Wenzel, G Wenzel, M Klauke, J Kerl, and K Hund-Rinke.
• Krankenhaus Kloster Grafschaft, Zentrum für Pneumologie, Beatmungs- und Schlafmedizin, Schmallenberg. M.Wenzel@fkkg.de
• Pneumologie. 2008 Jun 1; 62 (6): 324-9.

IntroductionPatients receiving mechanical ventilation and oxygen therapy frequently complain about the dryness of their airways. Humidifiers increase air humidity by generating water vapour and thus preventing the mucosa from desiccation. In this bench study, we compared the efficiency of several humidifiers.MethodsTwo identical humidifiers of each type (HC 602, HumiCare 200, Humid Aire 2i, minni-Max, MR 730 AGM, REMstar, Sirius, Somnia2, Somno Comfort2, VENTIclick, VIVO 30) were measured at three different heating intensities (low, medium, high) and three different flow rates (20, 55 and 90 l/min). The relative humidity at the exit of the tube and the temperature of the water in the heating chamber were registered. Additionally, we measured the humidity of the oxygen humidifier Respiflo at 1 - 5 l/min, the Respiflo was filled with either NaCl 0.9% or Aqua dest. Measurements were taken in a climatic chamber at 20 degrees C and 50% relative humidity. The atmospheric pressure was taken into consideration.ResultsThe MR 730 AGM and Humicare 200 generated a constant relative humidity of 100%. Among the remaining humidifiers, only the HC 602, HumidAire 2i and REMstar reached a humidity of about 95% at high flow rates. The Minni-Max, Somnia2 and VIVO 30 generated a humidity of 95% still at a flow rate of 55 l/min. The Sirius, Somno Comfort2 and the VENTIclick generated this amount of humidity only at low flow rates of 20 l/min. The three humidifiers mentioned last generated a relative humidity of only 68 - 76 at high flow rates of 90 l/min. The Respiflo generates a humidity of about 90% at each flow rate (1 - 5 l/min.), independent of being filled with NaCl 0.9% or Aqua dest.ConclusionFactors determinating the efficacy of humidifiers are the velocity of the airstream, the temperature of the water, the contact surface of the air and water compartments and the turbulence of the airstream. In vivo the amount of leakage is a very important determinant for the velocity of the airstream. In the care of mechanically ventilated patients one should have an approximate idea of the magnitude of the applied air flows. The limitations of some humidifiers should be known. The simple presence of a humidifier in combination with a respirator does not mean that the problem of dryness of the airway mucosa is eliminated.

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