With regards to the use of high-flow nasal oxygen therapy in adults:

a) Describe the mechanisms by which high flow nasal oxygen therapy is believed to exert its beneficial effects.

b) List two potential adverse effects associated with the use of high-flow nasal oxygen therapy.

c) List two relative contraindications to the use of high-flow nasal oxygen therapy.

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College Answer

a)

  • Precise mechanism of benefit is yet to be elucidated.
  • Increased FiO2:
    • Gas inlet flow limits secondary room air entrainment.
    • Provides anatomic oxygen reservoir in nasopharynx and oropharynx.
    • Rinsing of airway deadspace with oxygen.
  • CPAP effect:
    • decreases atelectasis and improves V-Q matching.
    • improves compliance.
    • decreases work of breathing by counteracting intrinsic PEEP.
  • Greater comfort:
    • Warmed and humidified oxygen can be better tolerated, therefore better compliance from patients.

b)

  • Pressure areas in the nose. Epistaxis.
  • Possible gastric distension.

c)

  • Nasal fracture.
  • Upper airway haemorrhage. Base of skull fracture.
  • Recent upper airway or aerodigestive tract surgery.

Discussion

There is a great article available (Ricard et al, 2012) which dissects this oxygen delivery system.

Describe the mechanisms by which high flow nasal oxygen therapy is believed to exert its beneficial effects.

  • PEEP effect
    • Though it seems to only be about 3cm H2O with 60L/min flow, when the mouth is open
    • If it works, then it has all the benefits of PEEP - recruitment of atelectatic lungs, decreased work of breathing, and so forth.
    • On top of that, it is supposed to overcome the "nasopharyngeal resistance" of obese OSA patients
    • In fact the benefits seem to be most pronounced in the obese patients- and the degree of improvement in gas exchange tends to be related to the degree of increase in end-expiratory lung volume, which suggests that there is a real alveolar recruitment effect.
  • Increased FiO2 -
    • The upper airways are "rinsed" with humidified oxygen; this is called the "pharyngeal dead space washout"; each breath drags more of this oxygenated air from this anatomical dead space and into the lungs.
    • The delivery of high flow oxygen at a high concentration cannot be accomplished reliably by oher low-flow means, such as the Venturi mask.
  • Increased comfort -
    • Apparently, its comofortable. The main reason for this is the fact that the mouth is left alsone, unlike most forms of CPAP.
    • Addtionally, the humidification of oxygen tends to decrease the nasty side effects of oxygen therapy, such as raw stripped mucosa

List two potential adverse effects associated with the use of high-flow nasal oxygen therapy.

  • Overdistension of the alveoli, and barotrauma
  • Discomfort associated with the device, its flow or the high temperature/humidity
  • Nasal mucosal damage due to high flow
  • Pressure areas due to the device
  • Failure to achieve the desired effect because of mouth-breathing
  • Overabundance of secretions (Velasco et al, 2014) - though some might view this as a desired effect
  • Epistaxis
  • Time-wasting (delaying the inevitable intubation)
  • Aspiration of food or upper airway secretions
  • Aspiration of circuit condensation water (there's no evidence that this causes pneumonia, but people complained about it in a survey of paediatric ICUs conducted by Manley et al, 2012)

List two relative contraindications to the use of high-flow nasal oxygen therapy.

References

References

Groves, Nicole, and Antony Tobin. "High flow nasal oxygen generates positive airway pressure in adult volunteers." Australian Critical Care 20.4 (2007): 126-131.

Ricard, J. D. "High flow nasal oxygen in acute respiratory failure." Minerva Anestesiol 78.7 (2012): 836-841.

Locke, Robert G., et al. "Inadvertent administration of positive end-distending pressure during nasal cannula flow." Pediatrics 91.1 (1993): 135-138.

O’Brien, Bj, J. V. Rosenfeld, and J. E. Elder. "Tension pneumo‐orbitus and pneumocephalus induced by a nasal oxygen cannula: Report on two paediatric cases." Journal of paediatrics and child health 36.5 (2000): 511-514.

Baudin, Florent, et al. "Modalities and complications associated with the use of high-flow nasal cannula: experience in a pediatric ICU." Respiratory care 61.10 (2016): 1305-1310.