Aerosol Risk with Noninvasive Respiratory Support in Patients with COVID-19

Acute Respiratory Failure From Early Pandemic COVID-19: Noninvasive Respiratory Support vs Mechanical Ventilation

BACKGROUND

The optimal strategy for initial respiratory support in patients with respiratory failure associated with COVID-19 is unclear, and the initial strategy may affect outcomes.

RESEARCH QUESTION

Which initial respiratory support strategy is associated with improved outcomes in patients with COVID-19 with acute respiratory failure?

STUDY DESIGN AND METHODS

All patients with COVID-19 requiring respiratory support and admitted to a large health care network were eligible for inclusion. We compared patients treated initially with noninvasive respiratory support (NIRS; noninvasive positive pressure ventilation by facemask or high-flow nasal oxygen) with patients treated initially with invasive mechanical ventilation (IMV). The primary outcome was time to in-hospital death analyzed using an inverse probability of treatment weighted Cox model adjusted for potential confounders. Secondary outcomes included unweighted and weighted assessments of mortality, lengths of stay (ICU and hospital), and time to intubation.

RESULTS

Nearly one-half of the 2,354 patients (47%) who met inclusion criteria received IMV first, and 53% received initial NIRS. Overall, in-hospital mortality was 38% (37% for IMV and 39% for NIRS). Initial NIRS was associated with an increased hazard of death compared with initial IMV (hazard ratio, 1.42; 95% CI, 1.03-1.94), but also an increased hazard of leaving the hospital sooner that waned with time (noninvasive support by time interaction: hazard ratio, 0.97; 95% CI, 0.95-0.98).

INTERPRETATION

Patients with COVID-19 with acute hypoxemic respiratory failure initially treated with NIRS showed an increased hazard of in-hospital death.

Use of high-flow nasal oxygen for pregnant women with COVID-19 in the labour ward setting

The presentation and management of SARS-CoV-2 (COVID-19) infection in the obstetric population is affected by the hormonal and mechanical changes of pregnancy. The increased oxygen demands in pregnancy in the face of conventional oxygen therapy, risks of tracheal intubation and discomfort from non-invasive positive pressure ventilation all support the use of high-flow nasal oxygen (HFNO) as an alternative therapy. The lack of published guidance for the use of HFNO has led to the development of local-level guidance based on expert consensus. More evidence exploring the use of HFNO therapy in the pregnant population is required to assist in developing clinical guidelines.

The COVID-19 Driving Force: How It Shaped the Evidence of Non-Invasive Respiratory Support

During the COVID-19 pandemic, the use of non-invasive respiratory support (NIRS) became crucial in treating patients with acute hypoxemic respiratory failure. Despite the fear of viral aerosolization, non-invasive respiratory support has gained attention as a way to alleviate ICU overcrowding and reduce the risks associated with intubation. The COVID-19 pandemic has led to an unprecedented increased demand for research, resulting in numerous publications on observational studies, clinical trials, reviews, and meta-analyses in the past three years. This comprehensive narrative overview describes the physiological rationale, pre-COVID-19 evidence, and results of observational studies and randomized control trials regarding the use of high-flow nasal oxygen, non-invasive mechanical ventilation, and continuous positive airway pressure in adult patients with COVID-19 and associated acute hypoxemic respiratory failure. The review also highlights the significance of guidelines and recommendations provided by international societies and the need for further well-designed research to determine the optimal use of NIRS in treating this population.

Acceptance and Tolerability of Helmet CPAP in Pediatric Bronchiolitis and Pneumonia: A Feasibility Study

Continuous positive airway pressure (CPAP) is a form of non-invasive ventilation used to support pediatric patients with acute respiratory infections. Traditional CPAP interfaces have been associated with inadequate seal, mucocutaneous injury, and aerosolization of infectious particles. The helmet interface may be advantageous given its ability to create a complete seal, avoid skin breakdown, and decrease aerosolization of viruses. We aim to measure tolerability and safety in a pediatric population in the United States and ascertain feedback from parents and health care providers. We performed a prospective, open-label, single-armed feasibility study to assess tolerability and safety of helmet CPAP. Pediatric patients 1 month to 5 years of age admitted to the pediatric intensive care unit with pulmonary infections who were on CPAP for at least 2 hours were eligible. The primary outcome was percentage of patients tolerating helmet CPAP for 4 hours. Secondary measures included the rate of adverse events and change in vital signs. Qualitative feedback was obtained from families, nurses, and respiratory therapists. Five patients were enrolled and 100% tolerated helmet CPAP the full 4-hour study period. No adverse events or significant vital sign changes were observed. All family members preferred to continue the helmet interface, nursing staff noted it made cares easier, and respiratory therapists felt the set up was easy. Helmet CPAP in pediatric patients is well-tolerated, safe, and accepted by medical staff and families in the United States future randomized controlled trials measuring its effectiveness compared with traditional CPAP interfaces are needed.

Outcomes in Patients with Acute Hypoxemic Respiratory Failure Secondary to COVID-19 Treated with Noninvasive Respiratory Support versus Invasive Mechanical Ventilation

Purpose

The goal of this study was to compare noninvasive respiratory support to invasive mechanical ventilation as the initial respiratory support in COVID-19 patients with acute hypoxemic respiratory failure.

Methods

All patients admitted to a large healthcare network with acute hypoxemic respiratory failure associated with COVID-19 and requiring respiratory support were eligible for inclusion. We compared patients treated initially with noninvasive respiratory support (noninvasive positive pressure ventilation by facemask or high flow nasal oxygen) with patients treated initially with invasive mechanical ventilation. The primary outcome was time-to-in-hospital death analyzed using an inverse probability of treatment weighted Cox model adjusted for potential confounders. Secondary outcomes included unweighted and weighted assessments of mortality, lengths-of-stay (intensive care unit and hospital) and time-to-intubation.

Results

Over the study period, 2354 patients met inclusion criteria. Nearly half (47%) received invasive mechanical ventilation first and 53% received initial noninvasive respiratory support. There was an overall 38% in-hospital mortality (37% for invasive mechanical ventilation and 39% for noninvasive respiratory support). Initial noninvasive respiratory support was associated with an increased hazard of death compared to initial invasive mechanical ventilation (HR: 1.61, p < 0.0001, 95% CI: 1.33 - 1.94). However, patients on initial noninvasive respiratory support also experienced an increased hazard of leaving the hospital sooner, but the hazard ratio waned with time (HR: 0.97, p < 0.0001, 95% CI: 0.96 - 0.98).

Conclusion

These data show that the COVID-19 patients with acute hypoxemic respiratory failure initially treated with noninvasive respiratory support had an increased hazard of in-hospital death.

Aerosol-Generating Procedures and Virus Transmission

During the early phase of the COVID-19 pandemic, many respiratory therapies were classified as aerosol-generating procedures. This categorization resulted in a broad range of clinical concerns and a shortage of essential medical resources for some patients. In the past 2 years, many studies have assessed the transmission risk posed by various respiratory care procedures. These studies are discussed in this narrative review, with recommendations for mitigating transmission risk based on the current evidence.

Quantification of aerosol dispersal from suspected aerosol-generating procedures

Background

Oxygen-delivering modalities like humidified high-flow nasal cannula (HFNC) and noninvasive positive-pressure ventilation (NIV) are suspected of generating aerosols that may contribute to transmission of disease such as coronavirus disease 2019. We sought to assess if these modalities lead to increased aerosol dispersal compared to the use of non-humidified low-flow nasal cannula oxygen treatment (LFNC).

Methods

Aerosol dispersal from 20 healthy volunteers using HFNC, LFNC and NIV oxygen treatment was measured in a controlled chamber. We investigated effects related to coughing and using a surgical face mask in combination with the oxygen delivering modalities. An aerodynamic particle sizer measured aerosol particles (APS3321, 0.3–20 µm) directly in front of the subjects, while a mesh of smaller particle sensors (SPS30, 0.3–10 µm) was distributed in the test chamber.

Results

Non-productive coughing led to significant increases in particle dispersal close to the face when using LFNC and HFNC but not when using NIV. HFNC or NIV did not lead to a statistically significant increase in aerosol dispersal compared to LFNC. With non-productive cough in a room without air changes, there was a significant drop in particle levels between 100 cm and 180 cm from the subjects.

Conclusions

Our results indicate that using HFNC and NIV does not lead to increased aerosol dispersal compared to low-flow oxygen treatment, except in rare cases. For a subject with non-productive cough, NIV with double-limb circuit and non-vented mask may be a favourable choice to reduce the risk for aerosol spread.

High-flow nasal cannula or NIV oxygen treatment does not lead to an increase in aerosol dispersal compared to the use of low-flow nasal cannula oxygen. For a coughing patient, using dual-limb NIV may reduce the risk of aerosol spread.https://bit.ly/3AnoyJu

High-flow nasal cannula therapy in a predominantly African American population with COVID-19 associated acute respiratory failure

Importance

Use of non-invasive respiratory modalities in COVID-19 has the potential to reduce rates of intubation and mortality in severe disease however data regarding the use of high-flow nasal cannula (HFNC) in this population is limited.

Objective

To interrogate clinical and laboratory features of SARS-CoV-2 infection associated with high-flow failure.

Design

We conducted a retrospective cohort study to evaluate characteristics of high-flow therapy use early in the pandemic and interrogate factors associated with respiratory therapy failure.

Setting

Multisite single centre hospital system within the metropolitan Detroit region.

Participants

Patients from within the Detroit Medical Center (n=104, 89% African American) who received HFNC therapy during a COVID-19 admission between March and May of 2020.

Primary outcome

HFNC failure is defined as death or intubation while on therapy.

Results

Therapy failure occurred in 57% of the patient population, factors significantly associated with failure centred around markers of multiorgan failure including hepatic dysfunction/transaminitis (OR=6.1, 95% CI 1.9 to 19.4, p<0.01), kidney injury (OR=7.0, 95% CI 2.7 to 17.8, p<0.01) and coagulation dysfunction (OR=4.5, 95% CI 1.2 to 17.1, p=0.03). Conversely, comorbidities, admission characteristics, early oxygen requirements and evaluation just prior to HFNC therapy initiation were not significantly associated with success or failure of therapy.

Conclusions

In a population disproportionately affected by COVID-19, we present key indicators of likely HFNC failure and highlight a patient population in which aggressive monitoring and intervention are warranted.

The Role of Noninvasive Respiratory Management in Patients with Severe COVID-19 Pneumonia

Acute hypoxemic respiratory failure is the principal cause of hospitalization, invasive mechanical ventilation and death in severe COVID-19 infection. Nearly half of intubated patients with COVID-19 eventually die. High-Flow Nasal Oxygen (HFNO) and Noninvasive Ventilation (NIV) constitute valuable tools to avert endotracheal intubation in patients with severe COVID-19 pneumonia who do not respond to conventional oxygen treatment. Sparing Intensive Care Unit beds and reducing intubation-related complications may save lives in the pandemic era. The main drawback of HFNO and/or NIV is intubation delay. Cautious selection of patients with severe hypoxemia due to COVID-19 disease, close monitoring and appropriate employment and titration of HFNO and/or NIV can increase the rate of success and eliminate the risk of intubation delay. At the same time, all precautions to protect the healthcare personnel from viral transmission should be taken. In this review, we summarize the evidence supporting the application of HFNO and NIV in severe COVID-19 hypoxemic respiratory failure, analyse the risks associated with their use and provide a path for their proper implementation.

Airway management in the adult patient with COVID-19: High flow nasal oxygen or not? A summary of evidence and local expert opinion

The use of high flow nasal oxygen in the care of COVID-19-positive adult patients remains an area of contention. Early guidelines have discouraged the use of high flow nasal oxygen therapy in this setting due to the risk of viral spread to healthcare workers. However, there is the need to balance the relative risks of increased aerosol generation and virus transmission to healthcare workers against the role high flow nasal oxygen has in reducing hypoxaemia when managing the airway in high-risk patients during intubation or sedation procedures. The authors of this article undertook a narrative review to present results from several recent papers. Surrogate outcome studies suggest that the risk of high flow nasal oxygen in dispersing aerosol-sized particles is probably not as great as first perceived. Smoke laser-visualisation experiments and particle counter studies suggest that the generation and dispersion of bio-aerosols via high flow nasal oxygen with flow rates up to 60 l/min is similar to standard oxygen therapies. The risk appears to be similar to oxygen supplementation via a Hudson mask at 15 l/min and significantly less than low flow nasal prong oxygen 1-5 l/min, nasal continuous positive airway pressure with ill-fitting masks, bilevel positive airway pressure, or from a coughing patient. However, given the limited safety data, we recommend a cautious approach. For intubation in the COVID-positive or suspected COVID-positive patient we support the use of high flow nasal oxygen to extend time to desaturation in the at-risk groups, which include the morbidly obese, those with predicted difficult airways and patients with significant hypoxaemia, ensuring well-fitted high flow nasal oxygen prongs with staff wearing full personal protective equipment. For sedation cases, we support the use of high flow nasal oxygen when there is an elevated risk of hypoxaemia (e.g. bariatric endoscopy or prone-positioned procedures), but recommend securing the airway with a cuffed endotracheal tube for the longer duration procedures when theatre staff remain in close proximity to the upper airway, or considering the use of a surgical mask to reduce the risk of exhaled particle dispersion.

High flow nasal cannula for adult acute hypoxemic respiratory failure in the ED setting: A narrative review

Introduction

High flow nasal cannula (HFNC) is a noninvasive ventilation (NIV) system that has demonstrated promise in the emergency department (ED) setting.

Objective

This narrative review evaluates the utility of HFNC in adult patients with acute hypoxemic respiratory failure in the ED setting.

Discussion

HFNC provides warm (37 °C), humidified (100% relative humidity) oxygen at high flows with a reliable fraction of inspired oxygen (FiO₂). HFNC can improve oxygenation, reduce airway resistance, provide humidified flow that can flush anatomical dead space, and provide a low amount of positive end expiratory pressure. Recent literature has demonstrated efficacy in acute hypoxemic respiratory failure, including pneumonia, acute respiratory distress syndrome (ARDS), coronavirus disease 2019 (COVID-19), interstitial lung disease, immunocompromised states, the peri-intubation state, and palliative care, with reduced need for intubation, length of stay, and mortality in some of these conditions. Individual patient factors play an important role in infection control risks with respect to the use of HFNC in patients with COVID-19. Appropriate personal protective equipment, adherence to hand hygiene, surgical mask placement over the HFNC device, and environmental controls promoting adequate room ventilation are the foundation for protecting healthcare personnel. Frequent reassessment of the patient placed on HFNC is necessary; those with severe end organ dysfunction, thoracoabdominal asynchrony, significantly increased respiratory rate, poor oxygenation despite HFNC, and tachycardia are at increased risk of HFNC failure and need for further intervention.

Conclusions

HFNC demonstrates promise in several conditions requiring respiratory support. Further randomized trials are needed in the ED setting.

Non-invasive oxygenation strategies for respiratory failure with COVID-19: A concise narrative review of literature in pre and mid-COVID-19 era

The coronavirus disease 2019 (COVID-19) has spread globally and can cause a shortage of medical resources, in particular, mechanical ventilators. High-flow nasal cannula oxygen therapy (HFNC) and non-invasive positive pressure ventilation (NPPV) are frequently used for acute respiratory failure patients as alternatives to invasive mechanical ventilation. They are drawing attention because of a potential role to save mechanical ventilators. However, their effectiveness and risk of viral spread are unclear. The latest network meta-analysis of pre-COVID-19 trials reported that treatment with non-invasive oxygenation strategies was associated with improved survival when compared with conventional oxygen therapy. During the COVID-19 pandemic, a lot of clinical research on COVID-19 related acute respiratory failure has been reported. Several observational studies and small trials have suggested HFNC or NPPV as an alternative of standard oxygen therapy to manage COVID-19 related acute respiratory failure, provided that appropriate infection prevention is applied by health care workers to avoid risks of the virus transmission. Awake proning is an emerging strategy to optimise the management of patients with COVID-19 acute respiratory failure. However, the benefits of awake proning have yet to be assessed in properly designed clinical research. Although HFNC and NPPV are probably effective for acute respiratory failure, the safety data are mostly based on observational and experimental reports. As such, they should be implemented carefully if adequate personal protective equipment and negative pressure rooms are available.

Airway Management in the Critically Ill Patient

Purpose of Review

This paper will evaluate the recent literature and best practices in airway management in critically ill patients.

Recent Findings

Cardiac arrest remains a common complication of intubation in these high-risk patients. Patients with desaturation or peri-intubation hypotension are at high risk of cardiac arrest, and each of these complications have been reported in up to half of all intubations in critically ill patient populations.

Summary

There have been significant advances in preoxygenation and devices available for performing laryngoscopy and rescue oxygenation. However, the risk of cardiovascular collapse remains concerningly high with few studies to guide therapeutic maneuvers to reduce this risk.

Aerosol generation with various approaches to oxygenation in healthy volunteers in the emergency department

OBJECTIVES

Health care workers experience an uncertain risk of aerosol exposure during patient oxygenation. To improve our understanding of these risks, we sought to measure aerosol production during various approaches to oxygenation in healthy volunteers in an emergency department.

METHODS

This was a prospective study conducted in an empty patient room in an academic ED. The room was 10 ft. long x 10 ft. wide x 9 ft. tall (total volume 900 ft3) with positive pressure airflow (1 complete turnover of air every 10 minutes). Five oxygenation conditions were used: humidified high-flow nasal cannula (HFNC) at 3 flow rates [15, 30, and 60 liters per minute (LPM)], non-rebreather mask (NRB) at 1 flow rate (15 LPM), and closed-circuit continuous positive airway pressure (CPAP) using the ED ventilator; in all cases a simple procedural mask was used. The NRB and HFNC at 30 LPM maneuvers were also repeated without the procedural mask, and CPAP was applied both with and without a filter. Each subject then sequentially underwent 8 total oxygenation conditions, always in the same order. Each oxygenation condition was performed with the participant on a standard ED bed. Particles were measured by laser aerosol spectrometer, with the detector sampling port positioned directly over the center of the bed, 0.35 meters away and at a 45-degree angle from the subject's mouth. Each approach to oxygenation was performed for 10 minutes, followed by a 20-minute room washout (≈ 2 complete room air turnovers). Particle counts were summated for 2 size ranges (150-300 nm and 0.5-2.0 μm) and compared before, during, and after each of the 8 oxygenation conditions.

RESULTS

Eight adult subjects were enrolled (mean age 42 years, body mass index 25). All subjects completed 8 oxygenation procedures (64 total). Mean particle counts per minute across all oxygenation procedures was 379 ± 112 (mean ± SD) for smaller aerosols (150-300 nm) and 9.3 ± 4.6 for larger aerosols (0.5-2.0 μm). HFNC exhibited a flow-dependent increase in particulate matter (PM) generation-at 60 LPM, HFNC had a substantial generation of small (55% increase) and large particles (70% increase) compared to 15 LPM. CPAP was associated with lowered small and large particle generation (≈ 10-15% below baseline for both sizes of PM). A patient mask limited particle generation with the NRB, where it was associated with a reduction in small and large particulates (average 40% and 20% lower, respectively).

CONCLUSION

Among 3 standard oxygenation procedures, higher flow rates generally were associated with greater production of both small and large aerosols. A patient mask lowered aerosol counts in the NRB only. Protocol development for oxygenation application should consider these factors to increase health care worker safety.

Evaluation and Management of the Physiologically Difficult Airway: Consensus Recommendations From Society for Airway Management

Multiple international airway societies have created guidelines for the management of the difficult airway. In critically ill patients, there are physiologic derangements beyond inadequate airway protection or hypoxemia. These risk factors contribute to the "physiologically difficult airway" and are associated with complications including cardiac arrest and death. Importantly, they are largely absent from international guidelines. Thus, we created management recommendations for the physiologically difficult airway to provide practical guidance for intubation in the critically ill. Through multiple rounds of in-person and telephone conferences, a multidisciplinary working group of 12 airway specialists (Society for Airway Management's Special Projects Committee) over a time period of 3 years (2016-2019) reviewed airway physiology topics in a modified Delphi fashion. Consensus agreement with the following recommendations among working group members was generally high with 80% of statements showing agreement within a 10% range on a sliding scale from 0% to 100%. We limited the scope of this analysis to reflect the resources and systems of care available to out-of-operating room adult airway providers. These recommendations reflect the practical application of physiologic principles to airway management available during the analysis time period.

Atteintes pulmonaires liées à la COVID-19

Le SARS-CoV-2, responsable de la COVID-19, est un nouveau bêta-coronavirus.

Il engendre une réaction inflammatoire intense pouvant aller jusqu’à l’« orage cytokinique », avec des atteintes pulmonaires épithéliales sévères et un tableau de coagulopathie intravasculaire pulmonaire.

Le tableau clinique est polymorphe, avec possible survenue d’un syndrome de détresse respiratoire aigu (SDRA).

La ventilation non invasive et l’oxygénothérapie à haut débit permettent de traiter efficacement plus de la moitié des patients graves sans recours à l’intubation et sans risque pour le personnel soignant.

Le seul traitement actuellement validé est la dexaméthasone à dose modérée (6 mg/j pendant 10 jours).

Le haut risque thrombotique justifie en fonction des cas une anticoagulation préventive voire curative.

Modes of Transmission of Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) and Factors Influencing on the Airborne Transmission: A Review

The multiple modes of SARS-CoV-2 transmission including airborne, droplet, contact, and fecal-oral transmissions that cause coronavirus disease 2019 (COVID-19) contribute to a public threat to the lives of people worldwide. Herein, different databases are reviewed to evaluate modes of transmission of SARS-CoV-2 and study the effects of negative pressure ventilation, air conditioning system, and related protection approaches of this virus. Droplet transmission was commonly reported to occur in particles with diameter >5 µm that can quickly settle gravitationally on surfaces (1-2 m). Instead, fine and ultrafine particles (airborne transmission) can stay suspended for an extended period of time (≥2 h) and be transported further, e.g., up to 8 m through simple diffusion and convection mechanisms. Droplet and airborne transmission of SARS-CoV-2 can be limited indoors with adequate ventilation of rooms, by routine disinfection of toilets, using negative pressure rooms, using face masks, and maintaining social distancing. Other preventive measures recommended include increasing the number of screening tests of suspected carriers of SARS-CoV-2, reducing the number of persons in a room to minimize sharing indoor air, and monitoring people's temperature before accessing a building. The work reviews a body of literature supporting the transmission of SARS-CoV-2 through air, causing COVID-19 disease, which requires coordinated worldwide strategies.

Aligning difficult airway guidelines with the anesthetic COVID-19 guidelines to develop a COVID-19 difficult airway strategy: a narrative review

The coronavirus disease 2019 (COVID-19) pandemic is caused by a coronavirus that is transmitted primarily via aerosol, droplets or direct contact. This may place anesthetists at higher risk of infection due to their frequent involvement in aerosol-generating airway interventions. Many anesthethetic COVID-19 guidelines have emerged, whose underlying management principles include minimizing aerosol contamination and protecting healthcare workers. These guidelines originate from Australia and New Zealand, Canada, China, India, Italy, Korea, Singapore, the United States and the United Kingdom. Hospitalized COVID-19 patients may require airway interventions, and difficult tracheal intubation secondary to laryngeal edema has been reported. Pre-pandemic difficult airway guidelines include those from Canada, France, Germany, India, Japan, Scandinavia, the United States and the United Kingdom. These difficult airway guidelines require modifications in order to align with the principles of the anesthetic COVID-19 guidelines. In turn, most of the anesthetic COVID-19 guidelines do not, or only briefly, discuss an airway strategy after failed tracheal intubation. Our article identifies and compares pre-pandemic difficult airway guidelines with the recent anesthetic COVID-19 guidelines. We combine the principles from both sets of guidelines and explain the necessary modifications to the airway guidelines, to form a failed tracheal intubation airway strategy in the COVID-19 patient. Valuing, and a greater understanding of, these differences and modifications may lead to greater adherence to the new COVID-19 guidelines.

Aerosol Risk with Noninvasive Respiratory Support in Patients with COVID-19

Objectives

This study evaluates aerosol production with high‐flow nasal cannula (HFNC) and noninvasive positive pressure ventilation (NIPPV) compared to 6 L/min by low‐flow nasal cannula.

Methods

Two healthy volunteers were randomized to control (6 L/min by low‐flow nasal cannula), NIPPV, or HFNC using block randomization. NIPPV conditions were studied using continuous positive airway pressures of 5, 10, and 15 cm H₂O with an FiO₂ of 1.0 delivered via full‐face mask. HFNC conditions included flow rates of 30 and 40 L/min with an FiO₂ of 1.0 with and without coughing. HFNC and low‐flow nasal cannula conditions were repeated with and without participants wearing a surgical mask. Six aerosol sizes (0.3, 1.0, 2.5, 5, and 10 µm) and total aerosol mass were measured at 2 and 6 ft from the participant's nasopharynx.

Results

There was no significant difference in aerosol production between either HFNC or NIPPV and control. There was also no significant difference with the use of a procedural mask over the HFNC. There was significant variation between the 2 participants, but in neither case was there a difference compared to control. There was an aerosol‐time trend, but there does not appear to be a difference between either flow rate, pressure, or control. Furthermore, there was no accumulation of total aerosol particles over the total duration of the experiment in both HFNC and NIPPV conditions.

Conclusions

HFNC and NIPPV did not increase aerosol production compared to 6 L/min by low‐flow nasal cannula in this experiment involving healthy volunteers.