[Is it necessary to humidify inhaled low-flow oxygen or low-concentration oxygen?].
In Japan, oxygen is routinely humidified in almost every hospital and clinic. In contrast, in Europe and North America, oxygen is not humidified as long as the oxygen flow is less than 4-5 L/min, according to the guidelines for oxygen therapy announced by the ACCP-NHLBI in 1984 and by AARC in 1992. In this paper, we demonstrate mathematically that: 1) the oxygen received through a nasal cannula at 0.5-4 L/min or through a Venturi mask at 24-40% constitutes only a small percentage of the patient's inspiratory tidal volume (2.4-19% and 3.8-24%, respectively), 2) the humidity deficit caused by inhaling unhumidified oxygen through a nasal cannula at 0.5-4 L/min or through a Venturi mask at 24% to 31% is very small compared with the water content delivered from the airway, and 3) this humidity deficit is easily compensated for by increasing the relative humidity of the room air a little, e.g., by only 4% in case of inhalation of 2 L/min of oxygen through a nasal cannula. Similar results are obtained when a Venturi mask is used to inhale oxygen. From these calculations, we conclude that routine humidification of low-flow oxygen or low-concentration oxygen is not justifiable in patients who need oxygen inhalation, as the humidity of room air is sufficient.
Department of Physical Therapy, Hokkaido University School of Health Science, N-12, W-5, Kita-Ku, Sapporo, Japan.
Kenji
K
Miyamoto
D006801:Humans; D006813:Humidity; D008432:Mathematical Computing; D010102:Oxygen Inhalation Therapy / Q000295:instrumentation / Q000379:methods*