The complete guide to high flow nasal cannula therapy (HFNC)

There is a range of terminology used for high flow nasal cannula (HFNC) therapy: HFNC supportive therapy, high flow therapy (HFT), nasal high flow (NHF), high flow (HF), high flow nasal cannula oxygen therapy, heated humidified high flow therapy (HHHF), high flow oxygen (HFO) therapy, and high flow oxygen therapy (HFOT). Hamilton Medical uses the term high flow nasal cannula (HFNC) therapy.

Good to know: The term HFNC refers to the therapy itself irrespective of the interface used (nasal cannula or tracheostomy connector).

High flow nasal cannula therapy is a type of respiratory support that delivers heated and humidified gas with a controlled concentration of oxygen to your patients. This therapy has become increasingly popular for hypoxemic respiratory failure.

HFNC is used during early noninvasive management of acute respiratory failure, and has proven to be safe and effective as a noninvasive ventilation method. HFNC has been shown to be potentially useful and efficient in other applications such as major postoperative care, immunocompromised patients, for preoxygenation, or during bronchoscopy (Ischaki E, Pantazopoulos I, Zakynthinos S. Nasal high flow therapy: a novel treatment rather than a more expensive oxygen device. Eur Respir Rev. 2017;26(145):170028. Published 2017 Aug 9. doi:10.1183/16000617.0028-20172​).

The system used to deliver HFNC requires the following components: a gas blender and flow meter, an active humidifier, a heated inspiratory circuit, and a nasal cannula or a tracheostomy connector as an interface. When we talk about high flow nasal cannula, we need to keep in mind the four elements that describe this therapy: flow, oxygen, heat, and humidity.

If we take a closer look at the meaning of each element, the advantages of using HFNC are clear:

• Flow: the higher flow rates allow you to set the inspiratory flow to adequately meet or even exceed the inspiratory demand of the patient.
• Oxygen: you can set the FiO2 more accurately within a range of 21% to 100%. However, consider escalating treatment if FiO2 of greater than 60% is needed to achieve the targeted SpO2.
• Heat: the gas should be heated to the core body temperature of 37°C (except during NIV where the default temperature is 31°C).
• Humidity: the breathing gas is saturated close to 100% relative humidity to meet the physiologic demands.

Good to know: Did you know that the inspiratory demands of adult patients with acute respiratory failure can range from 30 l/min to more than 120 l/min?

We can divide the benefits of HFNC into clinical and physiologic as follows.

Clinical benefits:

• Improved patient comfort and compliance with the treatment
• Better patient tolerance due to the warmth and humidity of inspired air
• Ease of use

Physiologic benefits:

• Improved oxygenation because higher inspiratory flows mean reduced oxygen dilution 
• Reduction of dead space and CO2 rebreathing compared with low flow oxygen therapy and NIV
• Reduced work of breathing associated with an improvement in respiratory rate, as well as a reduction in heart rate with a significant improvement in SpO2 measurements

Before we dive into the working principles of high flow nasal cannula, we need to address the limitations that are typical of low flow oxygen delivery systems. This will help you better understand the beneficial effects of HFNC for your patients.

With conventional oxygen delivery devices, the peak inspiratory flow rate in acute respiratory failure patients exceeds the delivered flow of oxygen. Typical low flow systems provide supplemental O2 directly to the airway at a flow of 8 l/min or less. This O2 provided by a low flow device is always diluted with ambient air (with 21% FiO2); the result is a low and variable FiO2. 

This variable FiO2 may be associated with one or more of the following: the interface used to deliver oxygen, the respiratory rate, the peak inspiratory flow and how the patient breathes (through the mouth or nose).

• Only 22% to 40% of oxygen at flow rates of up to 6 l/min in adults for low flow nasal cannulas
• Only 35% to 50% of oxygen at flow rates from 5 to 10 l/min for low flow oxygen masks

Good to know: The use of humidification is recommended when oxygen is supplied through a nasal cannula at flow rates of more than 4 l/min.

In contrast to low flow oxygen therapy, the gas flow rate and FiO2 in HFNC can be adjusted independently of one another, depending on the patient‘s inspiratory demands.

With high flow nasal cannula systems, the FiO2 is delivered more accurately and can be set from 21% to 100%.

As mentioned already, the higher flow rates are able to meet or even exceed the patient‘s peak inspiratory flow rate.

The blend of air and oxygen delivered to the patient is fully heated and humidified by the humidification chamber and the single limb heated breathing circuit. This breathing circuit contains heater wires within the tubing wall that minimize condensation.

The therapy is delivered directly into the patient‘s nostrils through a nasal cannula.

During normal inspiration, the PIF demand is 30 to 40 l/min. With high flow nasal cannula therapy, the administered FiO2 would equal the inhaled FiO2, while in the case of a low flow system, the inhaled FiO2 would be less than the administered FiO2 because it is diluted with ambient air (Roca O, Riera J, Torres F, Masclans JR. High-flow oxygen therapy in acute respiratory failure. Respir Care. 2010;55(4):408-413. 3​).

For higher flows, adequate humidification is fundamental because it improves the tolerance and compliance of the treatment. HFNC systems require an active heated humidifier to achieve optimal body temperature (37°C in adults and 34°C to 37°C in pediatric patients) with a humidity output of higher than 33 mg H2O/l and close to 100% of relative humidity.

The conditions provided by HFNC promote:

• Improved lung compliance
• Improved gas distribution in the lungs
• Improved mucociliary clearance
• Decreased airway resistance
• Increased patient comfort

HFNC is considered the first-line therapy for patients with acute hypoxemic respiratory failure and can be part of a treatment strategy, whether during escalation or weaning.

(Rochwerg B, Einav S, Chaudhuri D, et al. The role for high flow nasal cannula as a respiratory support strategy in adults: a clinical practice guideline. Intensive Care Med. 2020;46(12):2226-2237. doi:10.1007/s00134-020-06312-y4​) (Oczkowski S, Ergan B, Bos L, et al. ERS clinical practice guidelines: high-flow nasal cannula in acute respiratory failure. Eur Respir J. 2022;59(4):2101574. Published 2022 Apr 14. doi:10.1183/13993003.01574-20215​)

Negative end-expiratory transpulmonary pressure can cause ventilator-induced lung injury due to atelectrauma. Studies (Ricard JD, Roca O, Lemiale V, et al. Use of nasal high flow oxygen during acute respiratory failure. Intensive Care Med. 2020;46(12):2238-2247. doi:10.1007/s00134-020-06228-76​) have shown that HFNC has multiple physiologic effects ranging from improved lung volumes to decreased work of breathing. The main ones are as follows:

• High flow generates a washout effect in the upper airways, promoting anatomic dead-space clearance and CO2 removal
• Increases the end-expiratory lung volume and PaO2/FiO2 ratio
• Optimal strategy for administering oxygen to hypoxic critically ill patients with high respiratory demand
• Provision of low-level PEEP
• The therapy is delivered directly into the patient‘s nostrils through the nasal cannula

Amongst the main physiologic effects of HFNC are an increase in airway pressure and end-expiratory lung volume (EELV), and an improvement in oxygenation. These are more evident with higher flows of around 60 to 70 l/min. However, the beneficial effects on parameters such as dead-space washout, work of breathing, and respiratory rate may be achieved with intermediate flows (20 to 45 l/min)6.

Good to know: The physiologic effects of HFNC can be summarized as improved oxygenation, reduced work of breathing, improved lung protection and better comfort for the patient.

The nasal cannula interface is an essential component for delivery of high flow nasal cannula therapy. In order to maintain an effective flush of CO2, it is important that the cannula does not occlude more than ~50% of the nares.

Good to know: Airway pressure increases progressively with both increasing flow rate and nasal prong-to-nares ratio.

Below you can find the recommendations on how to set the flow and oxygen in adult and pediatric patients.

Important: Please note that they are only general recommendations, and every patient should be treated based on their specific medical condition.

• Set the flow initially to between 20 and 35 l/min
• The flow can be increased progressively in steps of 5 to 10 l/min if the respiratory rate fails to improve
• Increasing flows from 15 to 45 l/min triples the reduction in anatomic dead space
• To prevent intubation, choose the highest flow tolerated by the patient

(Drake MG. High-Flow Nasal Cannula Oxygen in Adults: An Evidence-based Assessment. Ann Am Thorac Soc. 2018;15(2):145-155. doi:10.1513/AnnalsATS.201707-548FR7​)

Flow rates that exceed inspiratory demand can be set in patients under 24 months who tolerate flows of 1 to 2 l/kg/min (up to 20 l/min).

(Kwon JW. High-flow nasal cannula oxygen therapy in children: a clinical review. Clin Exp Pediatr. 2020;63(1):3-7. doi:10.3345/kjp.2019.006268​)

The FiO2 is the concentration of oxygen in the gas mixture delivered to the patient. In HFNC, the FiO2 should be set as follows:

• You can set the FiO2 from 21% up to 100%.
• Titrate the FiO2 to achieve the desired SpO2 (target ranges of 92%–96% for most patients and 88%–92% for patients with chronic respiratory disease).

The ROX index is defined as the ratio of oxygen saturation as measured by SpO2/FiO2 to the respiratory rate. In patients with hypoxemic respiratory failure, the ROX index can be used after HFNC therapy has been initiated to help identify those who are at high risk of intubation (Roca O, Messika J, Caralt B, et al. Predicting success of high-flow nasal cannula in pneumonia patients with hypoxemic respiratory failure: The utility of the ROX index. J Crit Care. 2016;35:200-205. doi:10.1016/j.jcrc.2016.05.0229​).

ROX index ≥ 4.88 after two hours of treatment, indicates a high probability that intubation will not be necessary.

ROX index < 3.85 indicates a higher risk of treatment failure.

(Roca O, Messika J, Caralt B, et al. Predicting success of high-flow nasal cannula in pneumonia patients with hypoxemic respiratory failure: The utility of the ROX index. J Crit Care. 2016;35:200-205. doi:10.1016/j.jcrc.2016.05.0229​)

SpO2 is one of the most important parameters to monitor during HFNC. It indicates whether FiO2 needs to be re-adjusted and is useful during FiO2 titration.

How to use SpO2 (If the SpO2 option is not installed, use external patient monitoringA​) measurement on your Hamilton Medical ventilator:

• Connect the sensor to the device and the patient
• Select the System tab
• Activate the SpO2 sensor

The monitoring shows the values of flow and oxygen over time so you can evaluate the therapy's progress.

How to monitor the progress of the therapy with your Hamilton Medical ventilator:

• Main monitoring parameters
• Control flow
• Oxygen

Trending graphs:

• Select either Control Flow or Oxygen

High flow nasal cannula therapy is available as an option on all our ventilators. We also offer compatible high flow interfaces and a compatible humidifier. In just a few steps, you can change the interface and use the same device and breathing circuit to accommodate your patient’s therapy needs. 

We also have some exclusive offers for HFNC enthusiasts where something exciting about high flow nasal cannula therapy is waiting you.