Submitted by Carissa Coghill, SRT

High flow nasal cannula (HFNC) as delivered with devices such as Airvo™ and Optiflow™ are increasingly used for patients with acute respiratory failure (Hess, 2015). These patients receiving high flow nasal cannula oxygen therapy could additionally benefit from inhaled drug delivery such as bronchodilators, but what is the most effective way for them to receive aerosol therapy while on HFNC?
Some studies have been conducted comparing different interfaces used to deliver aerosol therapy via HFNC. Some interfaces include the Aerogen® Solo device (a vibrating mesh nebulizer) placed downstream of the heated-humidification system, and HFNC with the Vapotherm® Aerogen Adaptor compatible with the Aerogen® Solo device.

Bhashyam, Wolf, Marcinkowski, Saville, Thomas, Carcillo & Corcoran (2008) evaluated the potential for delivery of aerosols by HFNC with the Aerogen® Solo device through an in vitro study looking at aerosol output and particle size. The study compared adult and pediatric cannulas all driven by a flow of 3 litres per minute (Lpm). The total output ranged from 8.4 percent (%) to 25.1% and from 18.6% to 26.9% respectively, of the nominal dose placed in the nebulizer with the breathing simulator and without. The median diameter of aerosol particles for the adult sized cannula were 2.2 ± 0.2 micrometers (µm) and 90% of the aerosol was smaller than 4.2 ± 0.4 µm. For the pediatric sized cannula, the median diameters of the aerosol particles were 1.9 ± 0.3 µm and 90% were smaller than 3.8 ± 0.5 µm. In this study, the greatest observed losses were in the nebulizer-humidifier, connectors, heated tubing and in the humidifier itself. The study concluded that aerosols could be delivered through HFNC. However, flows for HFNC are usually 30 to 50 Lpm in adults, which is much greater than the standard of 3 Lpm used for this study.

Another study conducted by Ari, Harwood, Sheard, Dailey & Fink (2011) was an in vitro comparison of both heliox and oxygen in pediatric aerosol delivery with HFNC. The study used the Aerogen® Solo device placed on the inspiratory inlet of the heated humidifier with a heated-wire circuit connecting the pediatric nasal cannula. Breathing simulator parameters were a tidal volume of 100 millileters (mL), a respiratory rate of 20 breaths per minute, and an inspiratory-time of 1.0 second. Albuterol (2.5 milligrams in 3 mL normal saline) was administered to pediatric patients on HFNC, with an oxygen and a heliox (80:20) mixture. The investigators used flows of 3 Lpm and 6 Lpm and measured the inhaled dose at each of these flows; at 3 Lpm, the inhaled dose was 11.41 percent (%) ± 1.54% for heliox and 10.65% ± 0.51% for oxygen, and at 6 Lpm the inhaled dose for heliox was 5.42% ± 0.54% and 1.95% ± 0.5% for oxygen. There was a notable decrease in delivered dose when flows increased from 3 to 6 Lpm. The study showed that with heliox as the driving gas, the inhaled drug dose was greater than with oxygen alone. Again, these flows are not significantly relevant to the typical flows used with HFNC.

Perry, Kesser, Geller, Selhorst, Rendle & Hertzog (2013) also conducted a study using a mesh nebulizer connected between the HFNC and the humidifier. They administered albuterol, which was then collected on a filter mounted to a breathing simulator programmed with age appropriate breathing patterns and rates. They used adult, pediatric and neonatal sized HFNC with differing flow rates: flows of 3, 5 and 8 Lpm were used for infant; 3, 5, 10 and 20 Lpm were used for pediatric; and 5, 10, 20 and 40 Lpm were used for adult. The inspired dose of albuterol for adult was 2.5, 0.8, 0.4 and 0.2 percent (%) for each flow rate. Most (60-80%) of the albuterol was accumulated in the adaptor, and for each cannula size there was a significant decrease in the inspired dose with an increasing flow rate. The inspired dose increased with larger diameter cannula. The study concluded that the amount of drug delivered was lower than expected to achieve a clinical response. The data extrapolated from this study does not support the use of aerosol therapy with HFNC.

In a survey conducted by Miller, Gentle, Tyler & Napolitano (2018), current HFNC practice was evaluated by surveying practicing pediatric respiratory therapists (RTs) on aerosol delivery. It was found that aerosol therapy was delivered by 75 percent (%) of the respondents to the survey and of that, 77% of RTs delivered it through a vibrating mesh nebulizer, 6% via a jet nebulizer, 13% decreased the flow of HFNC during drug delivery, and 23% took the patient off of HFNC to deliver the treatment with a metered dose inhaler (MDI) or jet nebulizer. The medications that were delivered were beta-2 agonists, corticosteroids, mucolytics, and other medications. Of note is that most practicing pediatric RTs surveyed used a vibrating mesh nebulizer, but this survey concluded that more research is needed on the delivery of aerosolized medications through HFNC.

Overall, the articles that were reviewed did not encourage aerosol therapy through HFNC, and the studies conducted looked at the use of a vibrating mesh nebulizer. Additionally, the studies were conducted at lower flow rates than what would typically be set for HFNC with Optiflow™ or Airvo™. The survey (miller et al., 2018) suggested that more practicing respiratory therapists used vibrating mesh nebulizers to administer aerosol therapy to patients on HFNC, but is that best practice? More research must be conducted to determine what the optimal method of aerosol therapy is for patients needing HFNC.

References

Aerogen® (2018). Retrieved from https://www.aerogen.com/aerogen-solo-3/

Airvo™ (2019). Retrieved from https://fphcare.com

Ari, A., Harwood, R., Sheard, M., Dailey, P., Fink, J. B. (2011).
In vitro comparison of heliox and oxygen in aerosol delivery using pediatric high flow nasal cannula. Pediatric Pulmonology, 46, 795-801. doi: 10.1002/ppul.21421.
Available from doi: 10.1002.ppul.21421

Bhashyam, A.R., Wolf, M.T., Marcinkowski, A.L., Saville, A., Thomas, K., Carcillo, J.A., Corcoran, T.E. (2008).
Aerosol delivery through nasal cannulas: An in vitro study. J Aerosol Med Pulmonary Drug Delivery, 21(2), 181-188.
Available from https://www.ncbi.nlm.nih.gov/pubmed/18518794

Golshahi, L., Longest, P.W., Azimi, M., Syed, A., Hindle, M. (2014).
Intermittent aerosol delivery to the lungs during high-flow nasal cannula therapy. Respiratory Care, 59(10), 1477. doi: 10.4187/respcare.02903.
Available from https://www.ncbi.nlm.nih.gov/pubmed/24917454

Hess, D. (2015).
Aerosol therapy during noninvasive ventilation or high-flow nasal cannula. Respiratory Care, 60(6), 880-889. doi:10.4187/respcare.04042.
Available from https://www.ncbi.nlm.nih.gov/pubmed/26070581

Miller, A., Gentle, M., Tyler, L., Napolitano, N. (2018).
High-flow nasal cannula in pediatric patients: A survey of clinical practice. Respiratory Care, 63(7), 896. doi: 10.4187/respcare.05961.
Available from https://www.ncbi.nlm.nih.gov/pubmed/29535260

Perry, S. A., Kesser, K. C., Geller, D. E., Selhorst, D. M., Rendle, J. K. & Hertzog, J. H. (2013).
Influences of cannula size and flow rate on aerosol drug delivery through the Vapotherm humidified high-flow nasal cannula System. Pediatric Critical Care Medicine, 13(5), 250-255. doi: 10.1097/PCC.0b013e31828a7f79.
Available from https://www.ncbi.nlm.nih.gov/pubmed/23628834

Vapotherm® (2019). Retrieved from https://vapotherm.com/aerogen-adapter/

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