ICM - Oxygen delivery devices

Question 1

What components are involved in high-flow nasal oxygen and what function do they perform?

Answer 1

1. Air oxygen blender - to allow appropriate mix of oxygen
2. Heater/Humidification chamber - to prevent secretions drying out, energy loss required to humidify high flow, patient comfort
3. Wide flexible tubing with corrugations - allow delivery of high flow of air-oxygen blend to patient (Hagen-Poiseuille principle)
4. Heater coil along length of tubing - maintain humidification of air and prevent cooling and patient energy consumption to warm air.
5. Soft nasal prongs - patient comfort and compliance

Question 2

What are the benefits of high-flow nasal oxygen?

Answer 2

H - heated and humidifiedI - inspiratory demands can be met 
F - FRC increased
L - lighter than CPAP mask
O - oxygen dilution minimised
W - washout of pharyngeal dead space and potential for reduction in alveolar deadspace/pCO2.

Question 3

What is dead space?

Answer 3

Dead space is where there is ventilation without perfusion.
Anatomical dead space refers to the upper airways that are not involved in gas exchange.
Physiological dead space is anatomical dead space plus alveolar dead space (V/Q mismatch).

Question 4

How does NIV/CPAP and HFNC affect dead space.

Answer 4

CPAP mask/hood increases anatomical dead space but may reduce the physiological dead space by improved alveolar recruitment and decreasing V/Q mismatch.HFNC does not increase anatomical dead space, but may reduce physiological dead space.

Question 5

What are the current potential uses of HFNC in intensive care?

Answer 5

1. De novo type 1 respiratory failure - FLORALI study found non-inferiority to NIV and may prevent invasive ventilation
2. Post-operative respiratory failure and improvement in atelectasis
3. During bronchoscopy
4. Pre-oxygenation and during intubation
5. Post-extubation respiratory distress