Question 17

College answer

Not available.

Discussion

The wording of this SAQ might have confused some people, as some trainees would have found it difficult to find the subtle difference between the indications for high flow nasal oxygen and the uses of high flow nasal oxygen. 

Fortunately, this question is a mutant hybrid offspring of Question 2 from the first  paper of 2013  and Question 3 from the first paper of 2017, which means the candidates should have been well prepared for it. Thus:

Indications

• For hypoxic respiratory failure, especially due to pneumonia
• For hypercapnic respiratory failure (though the evidence is weaker)
• Where NIV is poorly tolerated or inappropriate (eg. oesophageal surgery)
• Where intubation is not appropriate
• Apnoeic oxygenation pre-intubation

Contraindications:

• Nasal fracture
• Recent nasal surgery
• Base of skull fracture - you might induce a pneumocephalus and god knows what else
• Decreased level of consciousness 

Complications

• Overdistension of the alveoli, and barotrauma
  • In fact, in neonates this may lead to pneumothorax
• 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)

"Critically evaluate" in 6 minutes or less, omitting elements already covered in the preceding question and stripping a more comprehensive answer down to some kind of bare metal:

• Rationale:
  • ​​​​​Pharyngeal dead space washout
  • Improved oxygenation by PEEP effect (minor though it may be)
  • Improved oxygenation by oxygen dilution reduction (at high resp rates)
  • Benefits of humidification
  • Increased comfort
• Advantages:
  • ​​​​​​​Appropriate where NIV and intubation are not
  • Allows high FiO₂ otherwise impossible to safely achieve
  • Allows high flow rates of gas, beneficial in patients with increased respiratory effort
• Limitations:
  • ​​​​​​​​​​​​​​The patient must be able to protect their airway
  • The nose and base of skull must be intact and uninjured
  • Avoided in upper GI surgery (risk to anastomosis)
  • PEEP is not measured, and is completely unpredictable
  • Intubation may be delayed; the outcome may be worse.
• Evidence:
  • FLORALI trial (2015): improvement in 90 day mortality with HFNP 

  • PREOXYFLOW (2015): no difference when HFNP was used to preoxygenate for intubation

  • THRIVE (2014): greatly improved apnoea time in difficult intubation patients

  • S68 Hi-Flo study (2014): no difference with HFNP (babies with bronchiolitis)

  • BiPOP (2015): non-inferior to NIV in post-op CABG patients