Oxygen comes out of a wall tap/canister at 100% concentration, but you can adjust the flow rate on the tap/dial (0-15L/minute). Different delivery devices tolerate different flow rates. The FiO2 (percentage of oxygen delivery) is determined by the flow rate and delivery device.
Nasal cannula
Delivers 24-30%
Comfortable
Flow rate 1-4L/minute
Used for mild hypoxaemia and use in non-acute wards
Hudson simple face mask
Delivers 30-40%
Flow rate 5-10L/minute
Delivers slightly more oxygen than a nasal cannula but the precise FiO2 cannot be determined so a Venturi mask is often used instead
Venturi (air entrapment) mask
Delivers 24-60%
Oxygen delivery depends on mask: this is marked on the side of the mask, along with the appropriate flow rate setting
Often used in patients with COPD/type 2 respiratory failure so you know the precise FiO2 you are delivering
Types of Venturi mask:
Colour
Flow rate (L/min)
Oxygen delivery (%)
Blue
2-4
24
White
4-6
28
Yellow
8-10
35
Red
10-12
40
Green
12-15
60
Non-rebreather mask
Delivers 85-90% with 15L/minute flow rate
Mask with a reservoir bag and valve which stops almost all rebreathing.
Used for acutely unwell hypoxaemic patients
High flow nasal oxygen (e.g. Optiflow)
Delivers up to 100% with up to 60L/minute flow rate
The very high flow rate also creates a small positive airway pressure effect similar to CPAP
Used intype 1 respiratory failure as an alternative to CPAP or a non-rebreather mask
Non-invasive ventilation
CPAP (continuous positive airway pressure)
Delivers up to 100% oxygen
Air/oxygen delivered through a tight-fitting mask at constant positive pressure to keep alveoli open
Used intype 1 respiratory failure (e.g. due to sleep apnoea oracute LVF)
BiPAP (bi-level positive airway pressure)
Delivers up to 100% oxygen
Same system but with a high positive pressure on inspiration and a lower positive pressure on expiration
Used intype 2 respiratory failure with respiratory acidosis or exhaustion (e.g. due to COPD or neuromuscular diseases)
Invasive ventilation
BiPAP (bi-level positive airway pressure)
Delivers up to 100% oxygen. A ventilation bag or machine is attached to an artificial airway to ventilate lungs. Used in intensive care and theatre.
General points
Intubate if GCS ≤ 8 (risk of airway not protected)
Aim for oxygen saturations of 92-96% in most patients, but 88-92% in those at risk of hypercapnic respiratory failure (e.g. COPD)
If patient is requiring the maximal level of ward-based oxygen therapy (i.e. 15L non-rebreather mask or higher-flow Venturi) to maintain saturations, or they are in type 2 respiratory failure, or oxygen levels are not improving, involve seniors and/or intensive care for consideration of non-invasive or invasive ventilation
Do an ABG on any patient with oxygen saturations of <92% or high oxygen requirements
