High-flow nasal cannula

OVERVIEW

• high-flow nasal cannula (HFNC)
• aka heated humidified HFNC or high flow nasal prongs

USE

Hypoxic respiratory failure, e.g.:

• Community-acquired pneumonia
• Viral pneumonia (e.g. influenza)
• Acute asthma
• Cardiogenic pulmonary edema
• Pulmonary embolism
• Interstitial pneumonia
• Carbon monoxide poisoning

Need for high FiO2 oxygen delivery in settings such as:

• Intubation (pre-oxygenation and apnoeic oxygenation)
• Postextubation respiratory distress
• Do-not-intubate/ palliative settings
• Postcardiac surgery
• Oxygen supply during invasive procedures, e.g. BAL, TOE, upper GI endoscopy

Widely used in paediatrics and increasing so in adults (in HDU/ICU settings)

DESCRIPTION

• Oxygen and air source
• air-oxygen blender generates up to FiO2 1.0 at a flow rate of up to 60L/min
• active heated humidifier capable of providing 100% body humidity
• single limb heated inspiratory circuit (avoids heat loss and condensation)
• Lightweight, flexible delivery tubing
• adjustable head strap
• Soft and flexible nasal prongs
• different brands are available (e.g. Optiflow™)

METHOD OF DELIVERY

• select appropriate cannulae and circuit for patient size
• connect bag of sterile water to heater/ humdifier
• the water bag must run freely and be placed as high as possible above the humidifier to achieve flow of water into the humidifier chamber
• turn on heater/ humdifier and allow to warm up before use
• select non-invasive mode and set temperature (T37C)
• always use a blender, never use flow meter off wall delivering FiO2 100%
• set oxygen flow rate (up to 8 L/min on pediatric tubing, up to 60L/min in adults) — <10Kg 2 L per kg per minute — >10Kg 2 L per kg per minute (max flow 60 L/min) — start off at 6L/min and increase up to goal flow rate over a few minutes to allow patient to adjust to high flow
• set FiO2 (from 21% to 100%)
• place nasal cannulae on patient — ensure cannulae sit snugly in the patient’s nares
• Prongs should not totally occlude nares
• Titrate FiO2 and flow rate as required

MECHANISM

Humidification

• heated humidified gas flow preserves nasal mucosa and is more comfortable allowing high flows
• enhanced mucocilliary function

High FiO2

• high flow permits constant oxygen delivery even with high inspiratory flows from intense respiration efforts (oxygen dilution reduction)
• nasopharyngeal dead space washout decreases dead space, decreases CO2 rebreathing and provides an oxygen reservoir

CPAP effect

• mechanical splinting of the nasopharynx prevents supraglottic collapse and decreases nasopharyngeal resistance
• low levels of PEEP may contribute to alveolar recruitment (decreased dead space), improved compliance and decreased work of breathing (to overcome iPEEP)

The mechanisms for HFNC remain poorly understood

OTHER INFORMATION

Performance

• HFNC can generate FiO2 1.0 and PEEP of up to 7.4 cmH20 at 60 L/min, but this is reduced at lower flow rates and if the nasal cannulae do not have a snug fit in the nares
• more comfortable and better compliance than a face mask
• observational data suggests that HFNC outperform face masks for relieving respiratory distress, improving oxygenation and preventing the need for NIV or intubation
• traditional unheated low-flow (≤ 6 L/min) diffuser humidifiers (“bubblers”) are much less effective

Disadvantages

• PEEP drops to ~2 cmH20 when the patient’s mouth is open
• PEEP is variable and not measurable
• more costly and requires more technology than standard nasal cannula
• critically ill patients may not be perceived as being so sick if they only have nasal cannulae on!

COMPLICATIONS

• local trauma, discomfort and pressure areas
• epistaxis
• excessive PEEP in neonates leading to pneumothorax
• gastric distension
• Blocked cannulae due to secretions
• Failure of HFNC might cause delayed intubation and worse clinical outcomes in patients with respiratory failure (Kang et al, 2015)

CONTRA-INDICATIONS

• epistaxis
• base of skull fracture
• surgery to the nose or upper aero-digestive tract
• nasal obstruction; e.g. nasal fracture, tenacious secretions, tumour

EVIDENCE

The precise role of high flow nasal cannulae in the management and prevention of hypoxia is controversial

• Failure of HFNC might cause delayed intubation and worse clinical outcomes in patients with respiratory failure (Kang et al, 2015)
• The FLORALI study, a small multicenter, open-label trial found that in patients with acute hypoxaemic respiratory failure and without hypercapnia, treatment with high-flow nasal oxygen, standard face mask oxygen, or non-invasive ventilation did not result in a significantly different intubation rates. There was a significant difference in favour of high-flow nasal oxygen in 90 day mortality (Frat et al, 2015; FLORALI study)
• Preoxygenation and apnoeic oxygenation
  • Compared to HFFM (high flow face mask), HFNC as a preoxygenation device did not reduce the lowest level of desaturation in an RCT (Vour’ch et al, 2015 – PREOXYFLOW trial)
  • A case series of 25 patients with difficult airways undergoing general anaesthesia for hypopharyngeal or laryngotracheal surgery had mean apnoea times of 14 minutes without desaturation (i.e. SaO2 >90%) (Pateal et al, 2015; THRIVE study)

References and Links

LITFL

• CCC — Preoxygenation
• CCC — Apnoeic oxygenation
• CCC — Delayed sequence intubation

Journal articles and textbooks

• Frat JP, Thille AW, Mercat A, et al. High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. N Engl J Med. 2015;372:(23)2185-96. [pubmed]
• Lee JH, Rehder KJ, Williford L, Cheifetz IM, Turner DA. Use of high flow nasal cannula in critically ill infants, children, and adults: a critical review of the literature. Intensive Care Med. 2013 Feb;39(2):247-57. PMID: 23143331.
• Miguel-Montanes R, Hajage D, Messika J, et al. Use of high-flow nasal cannula oxygen therapy to prevent desaturation during tracheal intubation of intensive care patients with mild-to-moderate hypoxemia. Crit Care Med. 2015;43:(3)574-83. [pubmed]
• Patel A, Nouraei SA. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia. 2015;70:(3)323-9. [pubmed]
• Ricard JD. High flow nasal oxygen in acute respiratory failure. Minerva Anestesiol. 2012 Jul;78(7):836-41. PMID: 22531566. [Free Fulltext]
• Ward JJ. High-flow oxygen administration by nasal cannula for adult and perinatal patients. Respir Care. 2013 Jan;58(1):98-122. doi: 10.4187/respcare.01941. PMID: 23271822. [Free Full Text]

FOAM and web resources

• EMCrit — Podcast 152 – High Flow Nasal Cannulae – Just Blowin’ Hot Air? (2015)
• EM Updates — The High Flow Nasal Cannula in the Emergency Department (2012)
• RCH PICU — High Flow Nasal Prong HFNP oxygen guideline
• ScanCrit — Humidified nasal high-flow oxygen (2012)
• Resus.ME — High flow nasal cannula oxygen (2013)
• Resus.ME — High flow systems for apnoeic oxygenation (2014)
• Brad Sobolewksi — High Flow Nasal Oxygen Set up (video)
• PulmCrit — Preoxygenation & apneic oxygenation using a nasal cannula by Josh Farkas (2014)