Humidity Outputs of Large-Reservoir Nebulizers

We measured the humidity output (HO) of five models of large-reservoir nebulizer to determine whether there were differences among models and what effect reservoir heating and oxygen concentration had on the humidity output. Method: Each nebulizer was attached to a T-piece, or Briggs setup and was powered by a 10-L/min flow of oxygen from a standard 50-psi source. Gas was drawn into a heated sample chamber, where the dew point was measured by a hygrometer, allowing the calculation of relative humidity (RH). Results: For unheated nebulizers, the mean RH output ranged from 58.0 to 78.8% at 37°C, and the differences among models were statistically significant when tested by analysis of variance. For heated nebulizers, the mean RH output ranged from 74.9 to 96.0%, and the differences among models were again statistically significant. HO was significantly increased by reservoir heating in all models, and when oxygen concentration had an effect, HO was greatest at the higher concentrations. Conclusions: Heating the nebulizer reservoir significantly improves the HO, and if the gas can be heated to body temperature at the patient connection, levels near body humidity can be delivered. Although the humidity differences among models were statistically significant, the ability to heat the nebulizer reservoir adequately appears to be more important than specific design in providing optimal humidity to the patient.