This article will explore the use of high-flow oxygen therapy via nasal cannula for the treatment of respiratory symptoms in COVID-19.

By Bill Pruitt, MBA, RRT, CPFT, AE-C

In December 2019, the first cases of a novel infection appeared in China and soon swept across the world to dominate almost all areas of life. Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), is the pathogen known to cause the Coronavirus Disease 2019 (COVID-19).1 As of the first of October, there have been over 35 million cases worldwide with some 66,000 critical cases and just over 1 million deaths.2 During the 11-month period that covers the pandemic, much has been learned about the virus, transmission, pathological changes, prevention, management and treatment. 

Patients who contract the COVID-19 virus have a wide range of issues, from asymptomatic to severe cases that can lead to death. Data suggest that racial and ethnic minorities have a higher risk of infection, hospitalization, and death.1 Transmission of the virus in humans is mainly through respiratory secretions but may also be transmitted through contaminated surfaces. The respiratory symptoms in COVID-19 infection are primary issues for the more serious cases and these patients’ conditions can change very rapidly. Efforts to maintain adequate oxygenation in some patients may move quickly from simple devices (ie traditional nasal cannula) to air-entrainment masks, nonrebreather masks, and/or high-flow nasal cannula, with ever-increasing flow and FiO2 needs. This article will provide a brief overview of COVID-19 and look closely at the use of high-flow nasal cannula therapy in the treatment of those with moderate or severe cases.

COVID-19: What We Know

Seven subgroups of coronaviruses have been identified. Four of these cause common cold symptoms in otherwise healthy individuals. The other three are known to cause severe illness. The first of these was a coronavirus strain that caused severe acute respiratory syndrome (SARS). It appeared in China and described in the literature as the SARS-CoV pandemic (2002-2003). The second appeared in the Arabian peninsula in 2012 and was the cause of the Middle East respiratory syndrome (MERS).4 SARS-CoV-2 (or COVID-19) was the third strain, first identified in December 2019 in China. By March 2020, the World Health Organization (WHO) designated the COVID-19 disease as a pandemic.

The average time of having symptoms occurs around 5 days after exposure to the virus and the majority of patients (97.5%) will show symptoms within 11 days. The most common symptoms are fever, dry cough, and shortness of breath and there are several other less common symptoms as well. Data from the US examining 1.3 million laboratory-confirmed cases show 14% of all cases of COVID-19 were hospitalized; 2% exhibited severe illness and were admitted to intensive care and 5% died.1 Supplemental oxygen is needed in a large percentage of hospitalized patients. Treatment for individuals with COVID-19 includes best practices for supportive management of acute hypoxic respiratory failure. Some patients who test positive for COVID-19 are asymptomatic but may later develop symptoms (described as presymptomatic). 

In a study of 3,711 people who were quarantined for 14 days on a cruise ship after one passenger tested positive, an estimated 17.9% were asymptomatic.3 It is thought that presymptomatic or truly asymptomatic patients are likely transmitting the virus, thus making it difficult to control its spread. Cases classified as mild have symptoms that resemble a common cold or mild case of influenza but no shortness of breath, dyspnea, or abnormal chest imaging. Cases classified as moderate exhibit lower respiratory disease evidenced by clinical assessment or radiographic imaging but have SpO2 readings >94% on room air. Severe cases exhibit tachypnea with a respiratory rate > 30 breaths/min, SpO2 readings <94% on room air, a PaO2/FiO2 ratio of <300 mmHg (where normal ratio is around 500 mmHg), or lung infiltrates showing up in >50% or the tissues. Cases classified as critical exhibit acute respiratory failure, septic shock, and/or dysfunction in multiple organ systems.1  

Early in the infectious process, the virus attacks nasal and bronchial epithelial cells and pneumocytes and gains entry by binding to the angiotensin-converting enzyme 2 (ACE2) receptor—particularly in the type II alveolar epithelial cells. This triggers an inflammatory response and an influx of monocytes and neutrophils. Alveolar wall thickening and edema appears, followed by formation of hyaline membranes. As the infection ramps up, the endothelial barrier is disrupted, dysfunctional alveolar-capillary oxygen transmission is reduced, and impaired oxygen diffusion capacity becomes a serious issue. Additionally, patients have increased coagulation and consumption of clotting factors with increased problems of deep vein thrombosis, pulmonary embolism, limb ischemia, stroke, and myocardial infarction.4 

High-flow Oxygen

Delivery of high-flow oxygen through a nasal cannula usually involves four components: 

  1. A gas blender to allow for a set FiO2 from 0.21 to 1.0;
  2. A nasal interface (cannula) with heated circuit to reduce rainout and preserve the temperature of the gas during delivery to the patient;
  3. A flow meter display to all for setting flow rates, and 
  4. A heated humidification system. 

Blended gas is delivered at flow rates that will meet or exceed the patient’s inspiratory demand (in adults this may require 40-60 LPM flow). The gas is warmed to body temperature (370C) and humidified (100% relative humidity at 370C).5 Several commercial HFNC devices (high-flow cannulas and circuits, high-flow generators with blenders, humidifiers and complete systems) are available.

The American Association for Respiratory Care (AARC) Guideline for SARS CoV-2 suggests supplemental oxygen once the SpO2 drops to below 92% and recommended if the SpO2 falls below 92%.6 This may be accomplished by traditional nasal cannula but if response is poor or absent, the strategy may shift to air-entrainment masks, non-rebreather masks, and/or high-flow nasal cannula. In patients with acute hypoxemic respiratory failure (AHRF), the AARC Guideline recommends keeping the SpO2 no higher than 96% and if conventional oxygen therapy approaches are not achieving the target SpO2 then high flow nasal cannula is suggested.6  

A study from France compared HFNC to standard oxygen therapy in a cohort of 379 patients diagnosed with COVID-19.  They found that HFNC significantly reduced the need to intubate and ventilate and that it was as safe as standard oxygen therapy but HFNC did not affect mortality.7 In a prospective randomized crossover study from Italy, researchers examined HFNC to oxygen therapy by face mask at approximately the same FiO2 settings. Their findings showed that HFNC significantly improved oxygenation, decreased respiratory rate and minute ventilation.8 

In a Respiratory Care journal review article of use of HFNC in adults, the authors state: “Available evidence suggests that, compared to O2 therapy, HFNC can reduce the risk of intubation for patients with acute hypoxemic respiratory failure, including those who are immunocompromised. However, evidence has not shown a benefit for length of hospital stay or mortality. The benefit of HFNC is more evident for patients with mild hypoxemia (PaO2/FiO2 > 200 mmHg).” 9

In some patients on HFNC and having a high inspiratory flow demand, a modification to the delivery of oxygen has been used to boost the FiO2 and resultant PaO2. One published article describes placing a regular aerosol mask with corrugated tubing (15 cm length) inserted into two lateral holes over the HFNC. The modified aerosol mask was termed a “double trunk mask.” This was applied to patients with moderate to severe AHRF and increased the PaO2 from 68 +14mm Hg to 85 +22 mm Hg (P<.001) and did not affect PaCO2 (P=0.18). The authors hypothesized that the double trunk mask reduced the entrainment of room air due to the patient’s high inspiratory demand (or due to mouth position) thus increasing the delivered FiO2.10  Another approach to improving oxygenation in patients receiving HFNC oxygen involves use of prone positioning.11-12  

Infection Risk

All bedside healthcare professional (HCP) who care for patients with COVID-19 are at increased risk of infection from the virus. Aerosol-producing procedures or therapies and procedures that induce coughing are suspected of releasing the virus into the air thus increasing the risk. In a letter published in the European Respiratory Journal in May 2020, the authors addressed the concerns of providing HFNC therapy in light of risk of infection. Oxygen therapy is of key importance in the treatment of COVID-19 and acute hypoxemia that is nonresponsive to standard, conventional therapy calls for HFNC or moving to higher levels of support (noninvasive ventilation, or intubation and mechanical ventilation).

After reviewing the scientific evidence the authors conclude that, “generation and dispersion of bio-aerosols via HFNC summarized here shows a similar risk to standard oxygen masks.” They also recommended that patients receiving HFNC therapy wear a surgical mask over the cannula to reduce the spread of the virus.13 Use of personal protective equipment (PPE) in caring for COVID-19 patients has been recommended by the Center for Disease Control and Prevention (CDC) and their website includes details on this equipment. It is recommended that HCWs wear an N95 or equivalent or higher-level respirator, eye protection, gloves, and a gown, that proper steps be taken in applying and removing this equipment, that proper handwashing practices be followed, and if available, patients be placed in airborne infection isolation rooms (AIIR). Other practices, such as distancing, barrier devices, cleaning and disinfection, are also covered through the CDC website.14


COVID-19 has brought on many changes and challenges. Hypoxemic patients are frequently seen and attempts to return them to normal oxygenation are included in the challenges faced everyday by respiratory therapists and the other healthcare team members. HFNC has been used to battle acute hypoxemic failure and is proving to be a valuable tool when used appropriately. Infection control and prevention has to be considered in all aspects of care to protect other patients, family members, and the healthcare team. HFNC therapy is often very effective in treating hypoxemia and comparable to other standard oxygen therapy approaches in aspects of safety. Its use may prevent having to move to higher, more expensive, and more invasive interventions to treat COVID-19 patients.


Bill Pruitt, MBA, RRT, CPFT, AE-C, FAARC, is a writer, lecturer, and consultant and recently retired from over 20 years teaching at the University of South Alabama in Cardiorespiratory Care. He also volunteers at the Pulmonary Clinic at Victory Health Partners in Mobile, Ala. For more information contact [email protected].

Featured image: Dräger’s HI-Flow Star HFNC. Product not available in the United States.


  1. COVID-19 Treatment Guidelines Panel. Coronavirus Disease 2019 (COVID-19) Treatment Guidelines. National Institutes of Health. Available at
  2. From the website
  3. Mizumoto K, et al. Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020. Eurosurveillance. 2020 Mar 12;25(10):2000180.
  4. Wiersinga WJ, et al. Pathophysiology, transmission, diagnosis, and treatment of coronavirus disease 2019 (COVID-19): a review. JAMA. 2020 Aug 25;324(8):782-93.
  5. AARC: “Adult Nasal High Flow Therapy: Informed and Educated.” 
  6. Branson RD, et al. American Association for Respiratory Care. SARS CoV-2: Guidance Document. American Association for Respiratory Care. 2020;9425.
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  11. Coppo A, et al. Feasibility and physiological effects of prone positioning in non-intubated patients with acute respiratory failure due to COVID-19 (PRON-COVID): a prospective cohort study. The Lancet Respiratory Medicine. 2020 Aug 1;8(8):765-74.
  12. Sun Q, et al. Lower mortality of COVID-19 by early recognition and intervention: experience from Jiangsu Province. Annals of Intensive Care. 2020 Dec;10(1):1-4.
  13. Li J, et al. High-flow nasal cannula for COVID-19 patients: low risk of bio-aerosol dispersion. ERJ. 2020 May 1;55(5).
  14. CDC: “Interim Infection Prevention and Control Recommendations for Healthcare Personnel During the COVID-19 Pandemic.” Accessed via Accessed 10/2/2020.