Filtration of Breathing Gases
By Ruben Restrepo, MD, RRT, FAARC

Patients and caregivers are often placed at risk for exposure to either pathogens in the form of infectious aerosol or a long list of aerosolized medications in the clinical setting. Filtration of breathing gases is therefore critical to eliminate any potential source of nosocomial infections and minimize the incidental exposure to any aerosolized medications and its side effects. Although the Centers for Disease Control and Prevention has clearly established standards that classify a filter as a high-efficiency particulate aerosol (HEPA) device, a variety of filters used in breathing circuits and heat and moisture exchange filters (HMEFs) may not provide the efficiency offered by HEPA-grade devices. The one important issue to keep in mind when questioning the quality of filters currently used in the clinical setting is that placement of bacterial filters on the expiratory limb has not conclusively demonstrated to reduce ventilator-associated pneumonia (VAP).

The following questions from our author to the respiratory care community. Please let us know your thoughts on these questions or if you have a question for the author.

1.  If regulatory agencies rigorously regulate the process of filling up gas cylinders and medical gas piping systems to prevent contamination of the gas, why would any department incur into additional expenses without scientific evidence of reducing nosocomial infections?
2. What about the associated resistance to flow these filters cause and the potential disruption of gas flow from ventilators that may increase patient’s work of breathing? Is using a filter worth the risk?
3. Is following universal precautions enough to replace the use of bacterial/viral filters?
4. A variety of modern HMEFs offer a greater than 99.99% filtration of particles less than 0.3 mm in diameter when airway pressures are less than 14 cm H2O. Should the clinician be concerned with the fact that most ventilated patients have airway pressures that exceed this standard?
5. Most HMEFs must be taken out of the circuit to allow nebulized drugs to reach the patient. This causes a circuit break and possibly leads to microaerosol emission to the environment. Since aerosol administration is quite common, would it be worth spending more money on HMEFs that divert the aerosol?