HFNC provides heated and humidified oxygen at high flows through a nasal cannula. It works by conditioning the gas, generating positive pressures, washing out dead space, and reducing work of breathing. HFNC can be used for respiratory distress, post-extubation, or weaning from other support. When using HFNC for COVID-19 patients, limit staff exposure, use airborne precautions, and have patients wear masks if possible.

1. High Flow Nasal Cannula (HFNC)
Mr. Ahmed Al Gahtani, BSRC, RRT.
Acting Chief, Pediatric Respiratory Care Services

2. Outlines
Introduction to HFNC
HFNC Mechanism of Action
HFNC Clinical Indications, Contraindication & Complications
HFNC Delivery Equipment
HFNC Setup & Clinical Application
Recommended Measures When Appling HFNC to COVID-19 Patients

3. H
H
HF
NC
HHHFNC refers to the administration of
heated, to body temperature (31 to 37
°C), humidified (> 99% relative humidity),
and adjustable high flow oxygen (meets
or exceeds the patient’s inspiratory flow)
at a concentration of 21% to 100% via a
nasal cannula
Heated
Humidified
High Flow

4. Introduction
• Humidified high flow nasal cannula therapy is a form of non-invasive respiratory support.
• HFNC is designed to administer a heated and humidified mixture of air and oxygen at a
flow higher than the patient’s inspiratory flow.
• There is currently no single, simple definition of high flow.
• In neonates/infants, it usually refers to the delivery of oxygen or an oxygen/room air
blend at flow rates greater than 2 to 3 L/min.
• In children, flow rates > 6 L/min are generally considered high flow.
• In number of published clinical practice guidelines the flow rates adjusted based on
body weight and recommend using 1 to 2 L/kg/min, which provides a degree of
distending pressure and reduces the work of breathing.
• High flow presents several advantages over conventional ‘low-flow’ oxygen therapy in
terms of humidification, oxygenation, gas exchange, and breathing pattern.

5. HFNC Mechanism of Action
• The HFNC mechanism of action which gives it superiority over conventional O2
therapy is based on four elements.
Gas Mixture
Conditioning
High Flow
Generated
Pressures
Reduced
Energy
Expenditure

6. HFNC Mechanism of Action
• Gas Mixture Conditioning: HFNC provides a relative humidity of nearly 100%
with the gas warmed to between 34°C and 37°C.
• Improves patient tolerance by reducing the sensation of respiratory distress
and mouth dryness.
• Improves mucociliary clearance.
• Improves inspiratory flow, which further increases the feeling of comfort.
• Heated and humidified gas diminishes the resistance in the nasal mucosa
induced by dry and cold gas.

7. HFNC Mechanism of Action
• High Flow: flow higher than the patient’s inspiratory flow provides better oxygen
delivery and aid in CO2 washing.
• The effect of a high flow on the oropharyngeal dead space, with the idea
being that the high flow of oxygen ‘washes out’ the end-expiratory oxygen-
depleted gas.
• In the next breath, the patient inhales pure oxygen.
• Dead space washout also reduces CO2 rebreathing.

8. HFNC Mechanism of Action
• Generated Pressures: high-flow mixture is likely to create a maximum positive
pharyngeal pressure of about 6 cm H2O during expiration.
• The pressure is determined not only by the flow, but also by the ratio of the
prong/nostril fit and whether the mouth is closed or not.
• The pressures generated by the device prevent pharyngeal collapse.
• Positive pressure during expiration prevents small airway collapse (stenting
effect), increases the expiratory time and reduces the auto-PEEP.
• Both effects, reduce the work of breathing.

9. • The physiological effects of high flow are based on
the CO2 washout effect of the nasopharyngeal dead
space and on the support of the inspiratory and
expiratory effort.
• During the expiratory phase patients are experiencing
some positive airway pressures whilst exhaling
against the flow into the nasopharynx. This PEEP
effect is commonly described in the range of 4–6
cmH2O.
• During the inspiratory phase the important
physiological effect of high flow is based on the
matching of the inspiratory demand of the patient
with the delivered flow rate.

10. HFNC Mechanism of Action
• Reduced Energy Expenditure: The high energy expenditure may lead to
respiratory muscle failure and recourse to mechanical ventilation. The risk of
decompensation is particularly high in young infants because their respiratory
muscles are poorly equipped with oxidative fibers.
• Several features of HFNC suggest positive effects on energy expenditure
compared with conventional oxygen therapy:
• Preserved mucociliary function,
• Prevention of atelectasis, and
• Decreased inspiratory work.

12. HFNC Clinical Indications, Contraindication &
Complications
• Clinical Indications:
• The prevention of, or relief from, hypoxemia with respiratory distress due to
bronchiolitis or pneumonia.
• Respiratory support to infants and children with chronic lung disease.
• HFNC therapy can be used if there is continuing hypoxemia (SpO2<90%) and
signs of moderate to severe respiratory distress despite oxygen therapy (like
in COVID-19 patients).
• There is provision for use of HFNC therapy on patients in mild respiratory
distress or who exhibit signs of increasing oxygen requirements in order to
prevent further deterioration.
• Weaning therapy from mask CPAP or BiPAP.
• Respiratory support post extubation and mechanical ventilation.

13. HFNC Clinical Indications, Contraindication &
Complications
• Contraindications:
• Critically ill infants and children requiring immediate higher level of
respiratory support i.e. NIV or invasive ventilation (especially in patients with
COVID-19)
• Upper airway obstruction
• Central apnea
• Asthma
• Blocked nasal passages/choanal atresia
• Trauma/surgery to nasopharynx
• Pneumothorax
• Decreased level of consciousness.

14. HFNC Clinical Indications, Contraindication &
Complications
• Complications:
• Abdominal distension.
• Pressure areas.
• Blocked HFNC due to secretions.
• Pneumothorax.

15. HFNC Delivery Equipment
• Nasal Cannula:
• The prong caliber is adapted to the nostril size in order to allow for leakage and
avoid overpressure phenomena.
• It may be useful for infants to reduce mouth leaks with a pacifier.
Vapotherm Nasal Cannula Fisher & Paykel Infant nasal cannula
Fisher & Paykel AIRVO 2 Optiflow
Junior Nasal Cannula

16. HFNC Delivery Equipment
• Flow Generator: Three types of gas generators are currently available
• The first type uses an air/oxygen blender and is connected to a system to
humidify and heat the gas. (Fisher and Paykel Optiflow System®) & Precision
Flow® (Vapotherm, Exeter, UK)

17. HFNC Delivery Equipment
• Flow Generator: Three types of gas generators are currently available
• The second type uses a turbine + humidifier (Airvo2®, Fisher and Paykel). This
system has the advantage of not requiring an external source of gas, except
oxygen. This device cannot be used with neonates and its start-up is sometimes a
bit long compared with other types.

18. HFNC Delivery Equipment
• Flow Generator: Three types of gas generators are currently available
• The third type is some conventional ventilators with an HFNC option & breathing
circuit connected to the humidifier. (Draeger VN500, Servo U & SLE6000)

19. HFNC Setup & Clinical Application
• HFNC Setup: will only cover uses an air/oxygen blender and is connected to a
system to humidify and heat.

20. HFNC Setup & Clinical Application
• HFNC Initial Settings: will only cover uses an air/oxygen blender and is
connected to a system to humidify and heat.
• Flow Rate: (follow unit specific protocol or doctor order) the is adapted from a
clinical practice guidelines
• ≤12Kg: 2 L/kg/minute
• >12Kg: 2 L/kg/minute for the first 12kg + 0.5L/kg/minute for each kg
thereafter.
• Increase flow to the prescribed rate over a few minutes, or as tolerated.
• Oxygen Concentration:
• Where supplemental oxygen is required, titrate FiO2 to the minimum amount
required in order to maintain target SpO2.

21. HFNC Setup & Clinical Application
• Patient Monitoring & Management:
• Continuous monitoring of SpO2 and HR until clinically stable
• Respiratory rate
• Heart rate
• Respiratory Distress (Work Of Breathing)
• SpO2

22. HFNC Setup & Clinical Application
• Patient Monitoring & Management:
• Within 2 hours it should be possible to reduce the FiO2 (where required) and
signs of clinical stabilization should be seen
• FiO2 required to maintain SpO2 in the target range should decrease to <40%.
• Heart rate should reduce by 20% or to within normal range.
• Respiratory rate should reduce by 20% or to within normal range.
• Signs of respiratory distress should improve.

23. HFNC Setup & Clinical Application
• Patient Monitoring & Management:
• Seek medical review if any of the following occurs:
• Patient is not stabilizing as described above.
• Degree of respiratory distress remains unchanged or worsens.
• Hypoxemia persists despite oxygen therapy.
• Requirement for >50% oxygen in patients without cyanotic heart disease
• Requirement for >30% oxygen in patients with cyanotic heart disease

24. HFNC Setup & Clinical Application
• Patient Monitoring & Management:
• Wean off HFNC when the child's clinical condition is improving as indicated by:
• Decreased work of breathing
• Normal or improved respiratory rate
• Return to normal cardiovascular parameters
• Wean FiO2 to 21% then cease HFNP therapy.
• HFNC therapy should not be routinely weaned, just stopped
• Consider transfer to low flow nasal cannula oxygen therapy where HFNc is no
longer required but clinical requirement for oxygen persists.

26. ORIGINAL ARTICLE
High-Flow Nasal Cannula in Very Preterm Infants after
Extubation
Brett J. Manley, M.B., B.S., Louise S. Owen, M.D., Lex W. Doyle, M.D., Chad C. Andersen, M.B., B.S., David W.
Cartwright, M.B., B.S., Margo A. Pritchard, Ph.D., Susan M. Donath, M.A., and Peter G. Davis, M.D.
New England Journal of Medicine
Although the result for the primary outcome was close to the margin of noninferiority, the efficacy of high-
flow nasal cannulae was similar to that of CPAP as respiratory support for very preterm infants after
extubation.

27. Large multicentre randomised trial will allow the definitive assessment of the efficacy of HFNC therapy as
compared to standard subnasal oxygen in the treatment of bronchiolitis.

30. Recommended
Measures When
Appling HFNC to
COVID-19
Patients

31. Recommended Measures When Appling HFNC
to COVID-19 Patients
• HFNC as a modality of noninvasive respiratory support is one of the
aerosol generating procedures the following should be applied:
• Healthcare Providers:
• Limit the number of staff exposed to patient on HFNC or when applying the
therapy.
• Isolation precautions  Standard + Contact + Droplet (or Airborne)
• Use appropriate PPE with (N95 Mask)
• Where: in Negative Pressure Room if available.
• Have the patient wear surgical mask over the nasal cannula if possible

32. References
• Egan's Fundamentals of Respiratory Care / Robert M. Kacmarek, James K.
Stoller, and Al Heuer. – 10th Edition, 2013
• Respiratory Care Principles and Practice / Dean R. Hess, et al – 2nd edition,
2012
• Neonatal and Pediatric Respiratory Care, Brian K. Walsh – 4th Edition, 2015
• Milési, C., Boubal, M., Jacquot, A., Baleine, J., Durand, S., Odena, M. P., &
Cambonie, G. (2014). High-flow nasal cannula: recommendations for daily
practice in pediatrics. Annals of intensive care, 4, 29.
https://doi.org/10.1186/s13613-014-0029-5
• World Health Organization, COVID-19 Publications
• SCCM, Pediatric Critical Care Medicine, Coronavirus Disease 2019 in
Critically Ill Children: A Narrative Review of the Literature