Many people wonder whether it is better to breathe though their nose or through their mouth; after all both ways get the job done. As a respiratory therapist, I recommend the nose. During inhalation though the nose, the turbinates increase the contact time between the mucosa and inspired air. As inspired air enters the nose, it is warmed via convection and picks up water vapor from the moist mucosal lining (evaporation), cooling the mucosal surface1. As the air reaches approximately 5cm below the carina (isothermic saturation boundary, ISB), the air achieves BTPS- body temperature (37oC) and ambient barometric pressure saturated (100% relative humidity). If the inspired air is not under BTPS as it enters the ISB, additional airway surfaces are required to make up for the humidity. We administer humidity therapy to patients who may not adequately humidify and warm their airways in cases such as the use of artificial airways, hypothermia, patients with bloody or thick secretions, patients with high spontaneous minute volumes, patients receiving in-line aerosol drug treatments etc. The amount of heat or humidity depends on the site of air/gas delivery1.
We use humidifiers to add molecular water to gases such as oxygen, or when overcoming humidity deficit created when the upper airway is bypassed. There are many devices used to provide humidification, which include bubble humidifiers, passover humidifiers, nebulizers of bland aerosols, and vaporizers. Heated humidifier systems usually have controllers that generate the temperature, prevent condensation, and overheating. Bland aerosol therapy is another way of humidifying the inspired air, but this strategy consists of liquid particles suspended in a gas, which may introduce pathogens into the respiratory tract1. Some aerosol generators include large volume nebulizers and ultrasonic nebulizers. Ultrasonic nebulizers use piezoelectric crystal to generate aerosol. The frequency at which the aerosol is generated determines the size of the aerosol particles. Particle size and aerosol density delivered to patients are also affected by flow and source of gas. Airway appliances used to deliver aerosol include face mask, tracheostomy mask, t-tube, and face tent. Aerosol mask would be used for patients with an intact upper airway, whereas a t-tube is used with mechanically ventilated patients. Placement of the nebulizer also affects the O2 concentration delivered to patients. It is possible to attach a flow meter with an O2 blender or an air-entrainment system to the chamber inlet to get a more precise control.
It is important to note that humidification often causes condensation buildup, which may result in cross contamination. Aerosol and condensate from ventilator circuits are great sources of bacterial colonization. Water traps are used to drain condensate away from the patient and to prevent disruption and occlusion of gas flow. Bland aerosols may cause bronchospasms that can be fatal to patients; therefore patients receiving continuous aerosol therapy should be carefully monitored and reevaluated every eight hours.
- Kacmrek, R. M., Stroller, J. K., & Heuer, A. J. (2013). History of respiratory care. In Robert Kacmrek, James Stroller, Albert Heuer (Ed.). United States: Elsevier Inc.
- Ari, A., Areabi, H., & Fink, J. B. (2010). Evaluation of aerosol generator devices at 3 locations in humidified and non-humidified circuits during adult mechanical ventilation. Respiratory Care, 55(7), 837-844 8p.
Respiratory Care 