The Safety of High Flow Nasal Cannula and Noninvasive Ventilation for Treatment of Patients With COVID-19 Complicated by Respiratory Failure

A novel coronavirus, subsequently named by the World Health Organization (WHO) as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged as the cause of atypical pneumonia linked to a seafood market in Wuhan, China in Dec 2019. Since then, SARS-CoV-2 related-disease (named COVID-19 by the WHO), has spread internationally to the scale of a global pandemic. Although most patients present with mild respiratory symptoms, some have severe pneumonia and a small proportion may become critically ill. Severe COVID-19 disease often progresses to acute hypoxemic respiratory failure requiring high fractional concentration of inspired oxygen (FiO2) and consideration for non-invasive ventilation (NIV) strategies.

High-flow nasal cannula (HFNC) has emerged as a non-invasive strategy improving oxygenation and carbon dioxide clearance by, in comparisons to other NIV strategies, better matching patients' inspiratory demands by delivering up to 60 L/min of gas flow and FiO2 up to 1.0. A systematic review found low certainty evidence suggesting benefit of HFNC in reducing the need for invasive mechanical ventilation (IMV) or escalation of oxygen therapy compared to conventional oxygen therapy (COT), and moderate certainty evidence suggesting no large difference in mortality. HFNC may reduce the need for IMV and associated complications such as ventilator-associated pneumonias, and alleviate the strain on healthcare systems during the COVID-19 pandemic.

COVID-19 spreads predominantly through respiratory droplets and fomites. There is concern, however, that airborne transmission may occur during respiratory procedures that generate aerosols. Airborne transmission involves smaller particles, typically <5μm in diameter, which may remain suspended in the air for extended periods of time, transmitted over distances greater than 1m, and inhaled into the lower airways. Reduction of respiratory particles to <5 µm involves evaporation of larger droplets and their contained organisms, and rehydration after deposition into the airway; therefore, airborne transmission is organism-specific, and requires the organism to survive a process of desiccation and aerosolization in sufficient numbers to cause infection. SARS-CoV2 has been shown to survive in air for 3 hrs after deliberate aerolization.

The Surviving Sepsis Campaign (SSC) COVID-19 guidelines provide a weak recommendation for the preferential use of HFNC over other NIV strategies in patients refractory to COT for type 1 respiratory failure.10 The use of high flow rates raises concerns that HFNC may cause aerosolization of infectious particles. Using a human patient simulator and smoke particles as markers visualized by a laser light sheet, HFNC with humidification may disperse exhaled air up to 172mm upward and 620mm laterally when the nasal cannula is clipped on properly and loosely respectively. Using the same methodology, NIV via the old generation oronasal masks could disperse exhaled air diffusely but there is limited exhaled air dispersion through the new generation masks with better design of the exhalation ports. In contrast, exhaled air dispersion from conventional nasal cannula delivering oxygen at 5L/min without humidification may disperse exhaled air to 1m towards the end of the bed.

Due to lack of field data on the use of these respiratory therapies in patients with COVID-19 complicated by respiratory failure, the role of fine particle aerosols in transmission of viral infection during application of HFNC and NIV is unknown. Because of uncertainty around the potential for aerosolization, the WHO has recommended that HFNC, NIV, including bubble CPAP, should be used with airborne precautions until further evaluation of safety can be completed. To alleviate concern by the healthcare workers in delivering these respiratory therapies to patients with COVID-19 complicated by respiratory failure, it is important to conduct a field test using viral samplers in patients with COVID-19 who require these therapies for respiratory failure.