Aerosol delivery through high-flow nasal therapy: Technical issues and clinical benefits

Abstract

High-flow nasal cannula (HFNC) therapy is an oxygen delivery method particularly used in patients affected by hypoxemic respiratory failure. In comparison with the conventional “low flow” oxygen delivery systems, it showed several important clinical benefits. The possibility to nebulize drugs via HFNC represents a desirable medical practice because it allows the administration of inhaled drugs, mostly bronchodilators, without the interruption or modification of the concomitant oxygen therapy. HFNC, by itself has shown to exert a small but significant bronchodilator effect and improves muco-ciliary clearance; thus, the nebulization of bronchodilators through the HFNC circuit may potentially increase their pharmacological activity. Several technical issues have been observed which include the type of the nebulizer that should be used, its position within the HFNC circuit, and the optimal gas flow rates to ensure an efficient drug delivery to the lungs both in “quiet” and “distressed” breathing patterns. The aim of this review has been to summarize the scientific evidence coming from “in vitro” studies and to discuss the results of “in vivo” studies performed in adult subjects, mainly affected by obstructive lung diseases. Most studies seem to indicate the vibrating mesh nebulizer as the most efficient type of nebulizer and suggest to place it preferentially upstream from the humidifier chamber. In a quite breathing patterns, the inhaled dose seems to increase with lower flow rates while in a “distressed” breathing pattern, the aerosol delivery is higher when gas flow was set below the patient’s inspiratory flow, with a plateau effect seen when the gas flow reaches approximately 50% of the inspiratory flow. Although several studies have demonstrated that the percentage of the loaded dose nebulized via HFNC reaching the lungs is small, the bronchodilator effect of albuterol seems not to be impaired when compared to the conventional inhaled delivery methods. This is probably attributed to its pharmacological activity. Prospective and well-designed studies in different cohort of patients are needed to standardize and demonstrate the efficacy of the procedure.

In Vivo Deposition of High-Flow Nasal Aerosols Using Breath-Enhanced Nebulization

“…Critically ill patients in the hospital are being placed on high-flow nasal cannula for the treatment of a variety of conditions that may be treated with continuous or bolus nebulization using conventional jet or mesh nebulizers. Reviews of in vitro and in vivo testing have concluded that the nasal gas flow rate must be reduced in order to mitigate aerosol losses, a maneuver with some complexity and risk [ 4 , 5 ]. It is true that aerosol losses increase with increases in high-flow rates.…”

“…Conventional nebulizers can support continuous nebulization, but the range of therapy for a given concentration of drug is limited by limitations in nebulizer output (e.g., 10 mL/h). For conventional mesh nebulizers, some authors suggest that nasal flows be reduced facilitating aerosol delivery [ 4 , 5 ].…”

Towards More Precise Targeting of Inhaled Aerosols to Different Areas of the Respiratory System

“…Only nebulizers and HFNC systems allow patients to inhale aerosol with spontaneous (i.e., not forced) breathing, which makes these inhaling devices the most versatile Ingelhein Boej [ 58 , 59 ]. In other cases, i.e., when the inhalation is restricted by the external resistance of the inhaler and requires the additional inspiratory effort of a patient, the flow function Q(t) (also: PIFR and AFR —see Figure 2 ) will be different.…”

Performance Characterisation of the Airvo2TM Nebuliser Adapter in Combination with the Aerogen SoloTM Vibrating Mesh Nebuliser for in Line Aerosol Therapy during High Flow Nasal Oxygen Therapy

“…The level of support can vary between invasive and non-invasive depending on the condition of the patient; it is delivered via endotracheal tube (ETT), tracheostomy tube (TT), mask, nasal cannula, or mouthpiece. High flow oxygen (HFO) therapy has become an increasingly implemented form of respiratory support as it can be used in both the hospital and homecare setting, improves patient oxygenation, reduces the work of breathing, and allows for concurrent delivery of aerosolised therapeutics for targeted treatment [ 2 , 3 , 4 , 5 ].…”