Impact of Gas Flow and Humidity on Trans-Nasal Aerosol Deposition via Nasal Cannula in Adults: A Randomized Cross-Over Study

Aerosol Delivery Efficiency With High-Flow Nasal Cannula Therapy in Neonatal, Pediatric, and Adult Nasal Upper-Airway and Lung Models

BACKGROUND

High-flow nasal cannula (HFNC) systems employ different methods to provide aerosol to patients. This study compared delivery efficiency, particle size, and regional deposition of aerosolized bronchodilators during HFNC in neonatal, pediatric, and adult upper-airway and lung models between a proximal aerosol adapter and distal aerosol circuit chamber.

METHODS

A filter was connected to the upper airway to a spontaneously breathing lung model. Albuterol was nebulized using the aerosol adapter and circuit at different clinical flow settings. The aerosol mass deposited in the upper airway and lung was quantified. Particle size was measured with a laser diffractometer. Regional deposition was assessed with a gamma camera at each nebulizer location and patient model with minimum flow settings.

RESULTS

Inhaled lung doses ranged from 0.2-0.8% for neonates, 0.2-2.2% for the small child, and 0.5-5.2% for the adult models. Neonatal inhaled lung doses were not different between the aerosol circuit and adapter, but the aerosol circuit showed marginally greater lung doses in the pediatric and adult patient models. Impacted aerosols and condensation in the non-heated HFNC and aerosol delivery components contributed to the dispersion of coarse liquid droplets, high deposition (11-44%), and occlusion of the supine neonatal upper airway. In contrast, the upright pediatric and adult upper-airway models had minimal deposition (0.3-7.0%) and high fugitive losses (∼24%) from liquid droplets leaking out of the nose. The high impactive losses in the aerosol adapter (56%) were better contained than in the aerosol circuit, resulting in less cannula sputter (5% vs 22%), fewer fugitive losses (18% vs 24%), and smaller inhaled aerosols (5 µm vs 13 µm).

CONCLUSIONS

The inhaled lung dose was low (1-5%) during HFNC. Approaches that streamline aerosol delivery are needed to provide safe and effective therapy to patients receiving aerosolized medications with this HFNC system.

Dos and don'ts to optimize transnasal aerosol drug delivery in clinical practice

INTRODUCTION

Transnasal aerosol drug delivery has become widely accepted for treating acutely ill infants, children, and adults. More recently aerosol administration to wider populations receiving high and low-flow nasal oxygen has become common practice.

AREAS COVERED

Skepticism of insufficient aerosol delivery to the lungs has been tempered by multiple in vitro explorations of variables to optimize delivery efficiency. Additionally, clinical studies demonstrated comparable clinical responses to orally inhaled aerosols. This paper provides essential clinical guidance on how to improve transnasal aerosol delivery based on device-, settings-, and drug-related optimization to serve as a resource for educational initiatives and quality enhancement endeavors at healthcare institutions.

EXPERT OPINION

Transnasal aerosol delivery is proliferating worldwide, but indiscriminate use of excessive-high flows, poor selection and placement of aerosol devices and circuits can greatly reduce aerosol delivery and efficacy, potentially compromising treatment to acute and critically ill patients. Attention to these details can improve inhaled dose by an order of magnitude, making the difference between effective treatment and the progression to more invasive ventilatory support, with greater inherent risk and cost. These revelations have prompted specific recommendations for optimal delivery, driving advancements in aerosol generators, formulations, and future device designs to administer aerosols and maximize treatment effectiveness.

Aerosol Delivery to Simulated Spontaneously Breathing Tracheostomized Adult Model With and Without Humidification

BACKGROUND

Optimal aerosol delivery methods for spontaneously breathing patients with a tracheostomy remain unclear. Thus, we aimed to assess the impact of nebulizer placement, flow settings, and interfaces on aerosol delivery by using a vibrating mesh nebulizer and a jet nebulizer in line with unheated humidification.

METHODS

An 8.0-mm tracheostomy tube was connected to the lung model that simulates adult breathing parameters via a collecting filter. Albuterol sulfate (2.5 mg/3 mL) was administered via a vibrating mesh nebulizer and a jet nebulizer, which was placed in line with unheated humidification provided by a large-volume nebulizer, with FIO2 set at 0.28, with gas flows of 2 L/min versus 6 L/min. Nebulizers were placed in line distal and proximal to the lung model by using a tracheostomy collar and a T-piece. Conventional nebulization was tested using a vibrating mesh nebulizer and a jet nebulizer directly connected to the tracheostomy tube bypassing the humidification device. The drug was eluted from the collecting filter and assayed with ultraviolet spectrophotometry (276 nm).

RESULTS

During in-line nebulizer placement with unheated humidification, the inhaled dose was 2-4 times higher with a gas flow of 2 L/min than 6 L/min, regardless of nebulizer type, placement, or interface (all P < .05). At 6 L/min, the inhaled dose was higher with proximal than distal placement when using both interfaces, but, at 2 L/min, the inhaled dose was lower with proximal placement. With a jet nebulizer, the tracheostomy collar generated a higher inhaled dose at proximal placement compared with the T-piece, whereas the T-piece resulted in a higher inhaled dose than the tracheostomy collar with distal placement, regardless of the flow settings. Compared with conventional nebulization using a vibrating mesh nebulizer, an in-line vibrating mesh nebulizer with a large-volume nebulizer at 2 L/min had a similar inhaled dose, regardless of nebulizer placement and interface. In contrast, the in-line jet nebulizer was influenced by both placement and interface.

CONCLUSIONS

Aerosol delivery with an in-line vibrating mesh nebulizer and jet nebulizer with unheated humidification was affected by nebulizer placement, interface, and gas flow settings.

In-Line Aerosol Therapy via Nasal Cannula during Adult and Paediatric Normal, Obstructive, and Restrictive Breathing

High-flow nasal oxygen therapy is being increasingly adopted in intensive and home care settings. The concurrent delivery of aerosolised therapeutics allows for the targeted treatment of respiratory illnesses. This study examined in-line aerosol therapy via a nasal cannula to simulated adult and paediatric models with healthy, obstructive and restrictive lung types. The Aerogen Solo vibrating mesh nebuliser was used in combination with the InspiredTM O2FLO high-flow therapy system. Representative adult and paediatric head models were connected to a breathing simulator, which replicated several different states of lung health. The aerosol delivery was quantified at the tracheal level using UV-spectrophotometry. Testing was performed at a range of supplemental gas flow rates applicable to both models. Positive end-expiratory pressure was measured pre-, during and post-nebulisation. The increases in supplemental gas flow rates resulted in a decrease in aerosol delivery, irrespective of lung health. Large tidal volumes and extended inspiratory phases were associated with the greatest aerosol delivery. Gas flow to inspiratory flow ratios of 0.29-0.5 were found to be optimum for aerosol delivery. To enhance aerosol delivery to patients receiving high-flow nasal oxygen therapy, respiratory therapists should keep supplemental gas-flow rates below the inspiratory flow of the patient.

In Vitro Model for Analysis of High-Flow Aerosol Delivery During Continuous Nebulization

BACKGROUND

To understand the fate of aerosols delivered by high-flow nasal cannula using continuous nebulization, an open-source anatomical model was developed and validated with a modified real-time gamma ratemeter technique. Mass balance defined circuit losses. Responsiveness to infusion rate and device technology were tested.

METHODS

A nasal airway cast derived from a computed tomography scan was converted to a 3-dimensional-printed head and face structure connected to a piston ventilator (breathing frequency 30 breaths/min, tidal volume 750 mL, duty cycle 0.50). For mass balance experiments, saline mixed with Technetium-99m was infused for 1 h. Aerosol delivery was measured using a gamma ratemeter oriented to an inhaled mass filter at the hypopharynx of the model. Background and dead-space effects were minimized. All components were imaged by scintigraphy. Continuous nebulization was tested at infusion rates of 10-40 mL/h with gas flow of 60 L/min using a breath-enhanced jet nebulizer (BEJN), and a vibrating mesh nebulizer. Drug delivery rates were defined by the slope of ratemeter counts/min (CPM/min) versus time (min).

RESULTS

The major source of aerosol loss was at the nasal interface (∼25%). Significant differences in deposition on circuit components were seen between nebulizers. The nebulizer residual was higher for BEJN (P = .006), and circuit losses, including the humidifier, were higher for vibrating mesh nebulizer (P = .006). There were no differences in delivery to the filter and head model. For 60 L/min gas flow, as infusion pump flow was increased, the rate of aerosol delivery (CPM/min) increased, for BEJN from 338 to 8,111; for vibrating mesh nebulizer, maximum delivery was 2,828.

CONCLUSIONS

The model defined sites of aerosol losses during continuous nebulization and provided a realistic in vitro system for testing aerosol delivery during continuous nebulization. Real-time analysis can quantify effects of multiple changes in variables (nebulizer technology, infusion rate, gas flow, and ventilation) during a given experiment.

Aerosol therapy in adult critically ill patients: a consensus statement regarding aerosol administration strategies during various modes of respiratory support

BACKGROUND

Clinical practice of aerosol delivery in conjunction with respiratory support devices for critically ill adult patients remains a topic of controversy due to the complexity of the clinical scenarios and limited clinical evidence.

OBJECTIVES

To reach a consensus for guiding the clinical practice of aerosol delivery in patients receiving respiratory support (invasive and noninvasive) and identifying areas for future research.

METHODS

A modified Delphi method was adopted to achieve a consensus on technical aspects of aerosol delivery for adult critically ill patients receiving various forms of respiratory support, including mechanical ventilation, noninvasive ventilation, and high-flow nasal cannula. A thorough search and review of the literature were conducted, and 17 international participants with considerable research involvement and publications on aerosol therapy, comprised a multi-professional panel that evaluated the evidence, reviewed, revised, and voted on recommendations to establish this consensus.

RESULTS

We present a comprehensive document with 20 statements, reviewing the evidence, efficacy, and safety of delivering inhaled agents to adults needing respiratory support, and providing guidance for healthcare workers. Most recommendations were based on in-vitro or experimental studies (low-level evidence), emphasizing the need for randomized clinical trials. The panel reached a consensus after 3 rounds anonymous questionnaires and 2 online meetings.

CONCLUSIONS

We offer a multinational expert consensus that provides guidance on the optimal aerosol delivery techniques for patients receiving respiratory support in various real-world clinical scenarios.

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

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.

The Impact of Head Model Choice on the In Vitro Evaluation of Aerosol Drug Delivery

There are variations in the values reported for aerosol drug delivery across in vitro experiments throughout the published literature, and often with the same devices or similar experimental setups. Factors contributing to this variability include, but are not limited to device type, equipment settings, drug type and quantification methods. This study assessed the impact of head model choice on aerosol drug delivery using six different adults and three different paediatric head models in combination with a facemask, mouthpiece, and high-flow nasal cannula. Under controlled test conditions, the quantity of drug collected varied depending on the choice of head model. Head models vary depending on a combination of structural design differences, facial features (size and structure), internal volume measurements and airway geometries and these variations result in the differences in aerosol delivery. Of the widely available head models used in this study, only three were seen to closely predict in vivo aerosol delivery performance in adults compared with published scintigraphy data. Further, this testing identified the limited utility of some head models under certain test conditions, for example, the range reported across head models was aerosol drug delivery of 2.62 ± 2.86% to 37.79 ± 1.55% when used with a facemask. For the first time, this study highlights the impact of head model choice on reported aerosol drug delivery within a laboratory setting and contributes to explaining the differences in values reported within the literature.

Lessons from COVID-19: A reflection on the strengths and weakness of early consensus recommendations for pediatric difficult airway management during a respiratory viral pandemic using a modified Delphi method

BACKGROUND

The authors recognized a gap in existing guidelines and convened a modified Delphi process to address novel issues in pediatric difficult airway management raised by the COVID-19 pandemic.

METHODS

The Pediatric Difficult Intubation Collaborative, a working group of the Society for Pediatric Anesthesia, assembled an international panel to reach consensus recommendations on pediatric difficult airway management during the COVID-19 pandemic using a modified Delphi method. We reflect on the strengths and weaknesses of this process and ways care has changed as knowledge and experience have grown over the course of the pandemic.

RECOMMENDATIONS

In the setting of the COVID-19 pandemic, the Delphi panel recommends against moving away from the operating room solely for the purpose of having a negative pressure environment. The Delphi panel recommends supplying supplemental oxygen and using videolaryngoscopy during anticipated difficult airway management. Direct laryngoscopy is not recommended. If the patient meets extubation criteria, extubate in the OR, awake, at the end of the procedure.

REFLECTION

These recommendations remain valuable guidance in caring for children with anticipated difficult airways and infectious respiratory pathology when reviewed in light of our growing knowledge and experience with COVID-19. The panel initially recommended minimizing involvement of additional people and trainees and minimizing techniques associated with aerosolization of viral particles. The demonstrated effectiveness of PPE and vaccination at reducing the risk of exposure and infection to clinicians managing the airway makes these recommendations less relevant for COVID-19. They would likely be important initial steps in the face of novel respiratory viral pathogens.

CONCLUSIONS

The consensus process cannot and should not replace evidence-based guidelines; however, it is encouraging to see that the panel's recommendations have held up well as scientific knowledge and clinical experience have grown.

Worldwide Clinical Practice of High-Flow Nasal Cannula and Concomitant Aerosol Therapy in the Adult ICU Setting

BACKGROUND

High-flow nasal cannula (HFNC) oxygen therapy has been broadly used. However, no consensus has been achieved on the practical implementation of HFNC and how to provide aerosol delivery during HFNC therapy in adult patients.

METHODS

An online anonymous questionnaire survey endorsed by 4 academic societies from America, Europe, mainland China, and Taiwan was administered from May to December 2019. Clinicians who had worked in adult ICUs for > 1 year and had used HFNC to treat patients within 30 days were included.

RESULTS

A total of 2,279 participants clicked on the survey link, 1,358 respondents completed the HFNC section of the questionnaire, whereas 1,014 completed the whole survey. Postextubation hypoxemia and moderate hypoxemia were major indications for HFNC. The initial flow was mainly set at 40-50 L/min. Aerosol delivery via HFNC was used by 24% of the participants (248/1,014), 30% (74/248) of whom reported reducing flow during aerosol delivery. For the patients who required aerosol treatment during HFNC therapy, 40% of the participants (403/1,014) reported placing a nebulizer with a mask or mouthpiece while pursuing HFNC whereas 33% (331/1,014) discontinued HFNC to use conventional aerosol devices. A vibrating mesh nebulizer was the most commonly used nebulizer (40%) and was mainly placed at the inlet of the humidifier.

CONCLUSIONS

The clinical utilization of HFNC was variable, as were indications, flow settings, and criteria for adjustment. Many practices associated with concomitant aerosol therapy were not consistent with available evidence for optimal use. More efforts are warranted to close the knowledge gap.

Delivered dose with jet and mesh nebulisers during spontaneous breathing, noninvasive ventilation and mechanical ventilation using adult lung models

What is the delivered dose with jet and mesh nebulisers during spontaneous breathing (SB), noninvasive ventilation (NIV), and mechanical ventilation (MV) using an adult lung model with exhaled humidity (EH)? The delivery of salbutamol sulfate (2.5 mg per 3 mL) with jet (Mistymax10) and mesh nebulisers (Aerogen Solo) was compared during SB, NIV, and MV using breathing parameters (tidal volume 450 mL, respiratory rate 20 breaths per min, inspiratory:expiratory ratio 1:3) with three lung models simulating exhaled humidity. A manikin was attached to a sinusoidal pump via a filter at the bronchi to simulate an adult with SB. A ventilator (V60) was attached via a facemask to a manikin with a filter at the bronchi connected to a test lung to simulate an adult receiving NIV. A ventilator-dependent adult was simulated through a ventilator (Servo-i) operated with a heated humidifier (Fisher & Paykel) attached to an endotracheal tube (ETT) with a heated-wire circuit. The ETT was inserted into a filter (Respirgard II). A heated humidifier was placed between the filter and test lung to simulate exhaled humidity (35±2°C, 100% relative humidity). Nebulisers were placed at the Y-piece of the inspiratory limb during MV and positioned between the facemask and the leak-port during NIV. A mouthpiece was used during SB. The delivered dose was collected in an absolute filter that was attached to the bronchi of the mannequin during each aerosol treatment and measured with spectrophotometry. Drug delivery during MV was significantly greater than during NIV and SB with a mesh nebuliser (p=0.0001) but not with a jet nebuliser (p=0.384). Delivery efficiency of the mesh nebuliser was greater than the jet nebuliser during MV (p=0.0001), NIV (p=0.0001), and SB (p=0.0001). Aerosol deposition obtained with a mesh nebuliser was greater and differed between MV, NIV, and SB, while deposition was low with a jet nebuliser and similar between the modes of ventilation tested.

Evaluation of Aerosol Therapy during the Escalation of Care in a Model of Adult Cystic Fibrosis

Lung disease is the main cause of morbidity and mortality in cystic fibrosis (CF). CF patients inhale antibiotics regularly as treatment against persistent bacterial infections. The goal of this study was to investigate the effect of clinical intervention on aerosol therapy during the escalation of care using a bench model of adult CF. Droplet size analysis of selected antibiotics was completed in tandem with the delivered aerosol dose (% of total dose) assessments in simulations of various interventions providing oxygen supplementation or ventilatory support. Results highlight the variability of aerosolised dose delivery. In the homecare setting, the vibrating mesh nebuliser (VMN) delivered significantly more than the jet nebuliser (JN) (16.15 ± 0.86% versus 6.51 ± 2.15%). In the hospital setting, using VMN only, significant variability was seen across clinical interventions. In the emergency department, VMN plus mouthpiece (no supplemental oxygen) was seen to deliver (29.02 ± 1.41%) versus low flow nasal therapy (10 L per minute (LPM) oxygen) (1.81 ± 0.47%) and high flow nasal therapy (50 LPM oxygen) (3.36 ± 0.34%). In the ward/intensive care unit, non-invasive ventilation recorded 19.02 ± 0.28%, versus 22.64 ± 1.88% of the dose delivered during invasive mechanical ventilation. These results will have application in the design of intervention-appropriate aerosol therapy strategies and will be of use to researchers developing new therapeutics for application in cystic fibrosis and beyond.

The impact of changing patient interfaces on delivering aerosol with titrated oxygen in the high flow system

INTRODUCTION

Despite the widespread oxygen-culture as more is better in prehospital and hospital settings, the use of titrated oxygen-flow within a high-flow system can be beneficial especially when combined with aerosol-delivery and also save the patient from unnecessary-hyperoxia.

METHODS

Forty-five COPD patients were included in this study where they allocated in three-groups (nasal-delivery, oral-delivery, and oronasal-delivery groups). All patients were received their inhaled-salbutamol dose using Aerogen Solo nebuliser by one of the three interfaces, eg, nasal-cannula, mouthpiece, and facemask in two conditions; with oxygen-flow and without any oxygen-flow. Pulmonary and systemic salbutamol deposition was estimated by collecting two urine-samples from the patient; 30 min post-inhalation and cumulatively 24 hr post-inhalation. The quantity of salbutamol in these collected samples was measured by high-performance liquid chromatography. Lung function measurement was performed pre-bronchodilator inhalation and 30 min post-bronchodilator to estimate the change in pulmonary functions post-inhalation regarding all tested interfaces.

RESULTS

COPD patients showed the highest salbutamol percentage excreted 30 min post-inhalation of 5.7% (1.4) with mouthpiece interface when combined with oxygen at P < .002. While with the same condition using oxygen, valved-facemask showed the highest salbutamol percentage excreted in 24 hr post inhalation samples but the difference is only significantly compared with nasal cannula (P < .006). Moreover, without oxygen delivery, mouthpiece and valved facemask showed approximately the same salbutamol percentage excreted in 30 min post-inhalation samples, higher than that delivered by nasal cannula (P < .001). Of note, salbutamol delivery is significantly increased with oxygen flow for all interfaces (P < .05) except with nasal cannula.

CONCLUSIONS

The nasal cannula is a more comfortable and tolerable interface despite the lower fraction of the delivered drug compared with other tested interfaces. The use of oxygen-flow with aerosol delivery within a high flow system positively affects the delivered drug fraction and the pulmonary deposition of the drug.

Narrative review of practical aspects of aerosol delivery via high-flow nasal cannula

Using high-flow nasal cannula (HFNC) as a "vehicle" to administer aerosolized medication has attracted clinicians' interest in recent years. In this paper, we summarize the current evidence to answer the common questions raised by clinicians about this new aerosol delivery route and best practices of administration. Benefits of trans-nasal aerosol delivery include increased comfort, ability to speak, eat, and drink for patients while meeting a range of oxygen requirements, particularly for those who need to inhale aerosolized medication for long periods. Aerosol administration via HFNC has been shown to be well tolerated by children and adults, with comparable or better delivery efficacy than other interfaces, ranging from 2-20%. In vitro and in vivo scintigraphy studies among pediatric and adult populations reported that the inhaled dose delivered via a vibrating mesh nebulizer is 2 to 3 fold greater than that via a jet nebulizer. For adults, placement of nebulizer at the inlet of humidifier increases inhaled dose while reducing rainout obstructing nasal prongs. When HFNC gas flow is set below patient inspiratory flow, aerosol deposition is higher than when the gas flow exceeds patient inspiratory flow; thus, if tolerated, titrating down HFNC gas flow during trans-nasal aerosol delivery, with close monitoring and the use of unit dose with high concentration are recommended. Trans-nasal pulmonary aerosol delivery has not been shown to increase bioaerosols generated by patients, but gas flow may disperse aerosols. Placement of a surgical or procedure mask over HFNC might reduce aerosol dispersion.

Pressurized Metered Dose Inhaler Aerosol Delivery Within Nasal High-Flow Circuits: A Bench Study

Background: Obstructive patients may benefit from nasal high-flow (NHF) therapy, but the use of pressurized metered-dose inhalers (pMDIs) has not been evaluated in this situation. Methods: Using an adult circuit and medium-sized cannula, we have tested different NHF rates, pMDI positions, breathing patterns, spacers, and spacer orientation. First, we evaluated albuterol delivery at the nasal cannula outlet. The second set of experiments made use of a nasopharyngeal cast to estimate the mass of albuterol potentially reaching the lungs. Albuterol was caught on filters placed at the cannula outlet and downstream of the nasal cast, and albuterol was quantified by spectrophotometry. Results: The highest amounts of albuterol delivered at the cannula outlet were observed with a 30 L/min flow rate (vs. 45 and 60 L/min) and placing the device close to the nasal cannula (in comparison with a position on the dry side of the humidification chamber). The use of a spacer was associated with higher delivery. The highest albuterol delivery was observed placing the spacer close to the nasal cannula, oriented for aerosol delivery following the gas flow and a 30 L/min NHF rate. Using this optimal setting, activating the pMDI at the beginning of inspiration (compared to expiration) increased albuterol delivery downstream of the nasopharyngeal cast. Whether in a quiet- or distress-breathing pattern, our measurements showed an amount of albuterol potentially delivered to the lungs exceeding 10% of the actuated dose in optimal conditions. Conclusions: The use of pMDIs is feasible to deliver albuterol within a NHF circuit. Using a spacer placed just upstream from the nasal cannulas, a low NHF rate and activating the pMDI at the beginning of inspiration was associated with drug delivery susceptible to induce bronchodilation, which will require to be tested in the clinical setting.

How to deliver aerosolized medications through high flow nasal cannula safely and effectively in the era of COVID-19 and beyond: A narrative review

Background

The treatments of COVID-19 involve some degree of uncertainty. Current evidence also shows mixed findings with regards to bioaerosol dispersion and airborne transmission of COVID-19 during high flow nasal cannula (HFNC) therapy. While coping with this global pandemic created hot debates on the use of HFNC, it is important to bring detached opinions and current evidence to the attention of health care professionals (HCPs) who may need to use HFNC in patients with COVID-19.

Aim

The purpose of this paper is to provide a framework on the selection, placement, and use of nebulizers as well as HFNC prongs, gas flow, and delivery technique via HFNC to help clinicians deliver aerosolized medications through HFNC safely and effectively in the era of COVID-19 and beyond.

Methods

We searched PubMed, Medline, CINAHL, and Science Direct to identify studies on aerosol drug delivery through HFNC using the following keywords: (“aerosols,” OR “nebulizers”) AND (“high flow nasal cannula” OR “high flow oxygen therapy” OR “HFNC”) AND (“COVID-19,” OR “SARS-CoV-2”). Twenty-eight articles including in vitro studies, randomized clinical trials, scintigraphy studies, review articles, prospective and retrospective research were included in this review.

Discussion and results

It is not clear if the findings of the previous studies on bacterial contamination could be applied to viral transmission because they do not provide data that could be extrapolated to the risk of SARS-CoV-2 transmission. In the face of the unknown risk with the transmission of COVID-19 during HFNC therapy, the benefits of HFNC must be weighed against the risk of infection to HCPs and other patients. Due to the limited number of ventilators available in hospitals and the confirmed effectiveness of HFNC in treating hypoxemic respiratory failure, HFNC may prevent early intubation, and prolonged intensive care unit stays in patients with COVID-19.

Conclusion

Clinicians should review the magnitude of this risk based on current evidence and use the suggested strategies of this paper for safe and effective delivery of aerosolized medications through HFNC in the era of COVID-19 and beyond.

Advances in Pulmonary Drug Delivery

Pulmonary drug delivery represents an attractive, non-invasive administration option. In addition to locally acting drugs, molecules that are intended to produce systemic effects can be delivered via the pulmonary route. Several factors need to be considered in the context of delivering drugs to or via the lungs—in addition to the drug itself, its formulation into an appropriate inhalable dosage form of sufficient stability is critical. It is also essential that this formulation is paired with a suitable inhaler device, which generates an aerosol of a particle/droplet size that ensures deposition in the desired region of the respiratory tract. Lastly, the patient’s (patho-) physiology and inhalation manoeuvre are of importance. This Special Issue brings together recent advances in the areas of inhalation device testing, aerosol formulation development, use of in vitro and in silico models in pulmonary drug deposition and drug disposition studies, and pulmonary delivery of complex drugs, such as vaccines, antibiotics and peptides, to or via the lungs.

A narrative review on trans-nasal pulmonary aerosol delivery

The use of trans-nasal pulmonary aerosol delivery via high-flow nasal cannula (HFNC) has expanded in recent years. However, various factors influencing aerosol delivery in this setting have not been precisely defined, and no consensus has emerged regarding the optimal techniques for aerosol delivery with HFNC. Based on a comprehensive literature search, we reviewed studies that assessed trans-nasal pulmonary aerosol delivery with HFNC by in vitro experiments, and in vivo, by radiolabeled, pharmacokinetic and pharmacodynamic studies. In these investigations, the type of nebulizer employed and its placement, carrier gas, the relationship between gas flow and patient’s inspiratory flow, aerosol delivery strategies (intermittent unit dose vs continuous administration by infusion pump), and open vs closed mouth breathing influenced aerosol delivery. The objective of this review was to provide rational recommendations for optimizing aerosol delivery with HFNC in various clinical settings.

The Clinical Impact of Flow Titration on Epoprostenol Delivery via High Flow Nasal Cannula for ICU Patients with Pulmonary Hypertension or Right Ventricular Dysfunction: A Retrospective Cohort Comparison Study

(1) Background: inhaled epoprostenol (iEPO) delivered via high-flow nasal cannula (HFNC) has been reported to be effective for pulmonary hypertension and right ventricular dysfunction. In vitro studies have identified HFNC gas flow as a key factor in trans-nasal aerosol delivery efficiency; however, little evidence is available on the clinical impact of flow titration on trans-nasal aerosol delivery. At our institution, iEPO via HFNC was initiated in 2015 and the concept of flow titration during iEPO via HFNC has been gradually accepted and carried out by clinicians in the recent years. (2) Methods: a retrospective review of the electronic medical records for all adult patients who received iEPO via HFNC in a tertiary teaching hospital. Pre- and post- iEPO responses were reported for patients whose HFNC flow was titrated or maintained constant during iEPO delivery. Positive response to iEPO was defined as the reduction of mean pulmonary arterial pressure (mPAP) > 10% for pulmonary hypertension patients or the improvement of oxygenation [pulse oximetry (SpO₂)/fraction of inhaled oxygen (F_IO₂)] > 20%. The number of responders to iEPO was compared between groups with titrated vs constant flow. (3) Results: 51 patients who used iEPO to treat pulmonary hypertension and/or right ventricular dysfunction were reviewed. Following iEPO administration via HFNC, mPAP decreased (43.6 ± 11.7 vs. 36.3 ± 9.7 mmHg, p < 0.001). Among the 51 patients, 24 had concomitant refractory hypoxemia, their oxygenation (SpO₂/F_IO₂) improved after iEPO delivery (127.8 ± 45.7 vs. 157.6 ± 62.2, p < 0.001). During iEPO initiation, gas flow was titrated in 25 patients and the remaining 26 patients used constant flow. The percentage of patients in the flow titration group who met the criteria for a positive response was higher compared to the group with constant flow (85.7% vs. 50%, p = 0.035). Pre- vs post-iEPO responses were significant in the flow titration group included improvement in cardiac output (p = 0.050), cardiac index (p = 0.021) and F_IO₂ reduction (p = 0.016). These improvements in hemodynamics and F_IO₂ were not observed in the constant flow group. (4) Conclusion: in patients with pulmonary hypertension and/or right ventricular dysfunction, trans-nasal iEPO decreased pulmonary arterial pressure. It also improved oxygenation in patients with combined refractory hypoxemia. These improvements were more evident in patients whose gas flow was titrated during iEPO initiation than those patients using constant flow.

In vitro comparison between inspiration synchronized and continuous vibrating mesh nebulizer during trans-nasal aerosol delivery

BACKGROUND

Compared to continuous vibrating mesh nebulizer (VMN), inspiration synchronized VMN has shown increased inhaled dose during noninvasive ventilation; however, its use during aerosol delivery via high-flow nasal cannula (HFNC) is still unknown.

METHODS

An adult manikin was connected to a dual-chamber model lung, which was driven by a critical care ventilator to simulate spontaneous breathing. A HFNC system was utilized with temperature at 37 ° C while gas flow at 5, 10, 20, 40, and 60 L/min. Inspiration synchronized and continuous aerosol generation were compared at different positions (at the inlet of humidifier vs close to patient). One milliliter of albuterol (2.5 mg/mL) was used in each run (n = 3). Collection filter was placed at the trachea and was removed after each run. Drug was eluted from the filter and assayed with UV spectrophotometry (276 nm).

RESULTS

When nebulizer was placed close to patient, inhaled dose was higher with inspiration synchronized than continuous aerosol generation at all gas flows (p = 0.05) except at 5 L/min. When placed at the inlet of humidifier, compared to continuous, inspiration synchronized aerosol generated higher inhaled dose with gas flow set below 50% of patient inspiratory flow [23.9 (20.6, 28.3)% vs 18.1 (16.7, 19.6)%, p < 0.001], but lower inhaled dose with gas flow set above 50% of patient inspiratory flow [3.5 (2.2, 9.3)% vs 9.9 (8.2, 16.4)%, p = 0.001]. Regardless of breathing pattern, continuous aerosol delivered greater inhaled dose with nebulizer placed at humidifier than close to patient at all gas flows except at 5 L/min.

CONCLUSION

When the HFNC gas flow was set higher than 50% of patient inspiratory flow, no significant advantage was found in inspiration synchronized over continuous aerosol. However, inspiration synchronized aerosol generated 30% more inhaled dose than continuous with gas flow set below 50% of patient inspiratory flow, regardless of nebulizer placement. Continuous nebulizer needs to be placed at the inlet of humidifier.