High flow oxygen therapy FAQs

Q. What is high flow oxygen therapy (HFOT)?

HFOT is a form of therapy that administers heated and humidified air plus supplementary oxygen (FiO2 from 21% to 100%) through a nasal cannula at a continuous flow of up to 60 L/min

Q. What are the main clinical indications for HFOT?

  • Non-hypercapnic acute hypoxemic respiratory failure1
  • Post-extubation period2

Q. What are other potential clinical indications for HFOT?

  • Pre-intubation
  • Patients undergoing bronchoscopy and other invasive procedures
  • Emergency department
  • Palliative care
  • Acute heart failure
  • Chronic airway disease

Q. What are the effects of HFOT?

  • HFOT washes out carbon dioxide from the patient’s anatomical dead space of the patient3
  • High flow oxygen creates an oxygen-enriched reservoir in the patient’s anatomical dead space while providing a flow to match or exceed the patient’s inspiratory demand. Thus, the patient’s work of breathing is reduced4
  • High flow creates a small positive nasopharyngeal pressure5

Q. What are the advantages of HFOT?

  • HFOT requires minimal technical skill to set up and apply – however, close monitoring is essential
  • Allows patients to speak and to eat6
  • Reduced sensation of respiratory distress7 and mouth dryness6– Improving patient comfort and tolerance
  • Heated and humidified gas flow preserves the mucociliary functions8

Q. Where is HFOT mainly used?

  • HFOT has widespread hospital applications due to its various indications for use
  • Most typical wards are:- Intensive Care Units (ICUs)- Emergency departments

Q. What is a typical hospital setup for delivering HFOT?

  • Gas source with flow and FiO2 control- Air/oxygen blender with flow meter (up to 60 L/min)
  • Patient interface- ResMed AcuCare HFNC

Q. Which parameters are set to provide HFOT?

  • Flow: Continuous gas flow of up to 60 L/min- To cover the patient’s spontaneous breathing pattern- FiO2 (fraction of inspired oxygen): from 21% to 100%- To ensure correct patient oxygenation for treatment of hypoxemia
  • Breathing gas humidity: ideally 100% relative humidity for a gas temperature between 34–37°C or (93–98°F)- To avoid dryness, and to maximise patient compliance

Q. What are the contraindications for HFOT?

  • High flow oxygen therapy is a form of positive airway pressure
  • Contraindications for positive airway pressure apply:- Pneumothorax- Pathologically low blood pressure- Cerebrospinal fluid leak

    – Recent cranial surgery or trauma

    – Severe bullous lung disease

    – Dehydration

Q. What are the differences between HFOT and conventional low flow oxygen therapy?

  • Conventional low flow oxygen therapy provides oxygen at flow rates up to 6 L/min when using standard low flow nasal cannulas, and a maximum of 15 L/min with non-rebreather masks
  • Low flow oxygen supplies flow rates lower than the patient‘s inspiratory demand, thus a mix of supplemental oxygen and room air is entrained9– No precise control of FiO2
  • The gas supplied to the patient is typically non-conditioned to the patient, that is, not heated or humidified10– Patient compliance might be reduced

Q. What are the differences between HFOT and non-invasive ventilation (NIV)?

  • HFOT is NOT ventilation
  • NIV can only be delivered by pressure or volume regulated ventilators
  • The patient interface is typically a full face or a nasal mask, preventing unintentional leak between cushion and patient skin
  • Ventilation is induced by several indications, such as chronic respiratory failure and acute respiratory failure with hypercapnic conditions

Q. Is an elevated noise level normal during HFOT?

  • HFOT may be perceived as noisy due to its continuous high flow of up to 60 L/min
  • When using an air/oxygen blender, ResMed recommends using a muffler between blender/flowmeter and humidifier to reduce the noise caused by the flow source.


1.Frat JP et al. High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. New England Journal of Medicine 2015;372(23):2185-96.

2.Maggiore SM et al. Nasal high-flow versus venturi mask oxygen therapy after extubation: effects on oxygenation, comfort and clinical outcome. American Journal of Respiratory and Critical Care Medicine 2014;190(3):282–8.

3.Dewan, NA, Bell CW. Effect of low flow and high flow oxygen delivery on exercise tolerance and sensation of dyspnea. A study comparing the transtracheal catheter and nasal prongs. Chest 1994;105(4):1061–5.

4.Dysart K et al. Research in high flow therapy: mechanisms of action. Respiratory Medicine 2009;103(10):1400–5.

5.Ritchie JE et al. Evaluation of a humidified nasal high-flow oxygen system, using oxygraphy, capnography and measurement of upper airway pressures. Anaesthesia and Intensive Care 2011; 39(6):1103–10

6.Roca O et al. High-flow oxygen therapy in acute respiratory failure. Respiratory Care 2010;55(4):408–13

7.Sztrymf B et al. Beneficial effects of humidified high flow nasal oxygen in critical care patients: a prospective pilot study. Intensive Care Medicine 2011;37(11):1780–6.

8.Hasani A et al. Domiciliary humidification improves lung mucociliary clearance in patients with bronchiectasis. Chronic Respiratory Disease 2008;5(2):81–6.

9.Bazuaye E et al. Variability of inspired oxygen concentration with nasal cannulas. Thorax 1992;47(8):609–11.

10.Chanques G et al. Discomfort associated with underhumidified high-flow oxygen therapy in critically ill patients. Intensive Care Medicine 2009;35(6):996–1003.