Table of Contents
Oxygen masks
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 in type 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 in type 1 respiratory failure (e.g. due to sleep apnoea or acute 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 in type 2 respiratory failure with respiratory acidosis or exhaustion (e.g. due to COPD or neuromuscular diseases)
Invasive ventilation
Invasive ventilation
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
- Humidified oxygen helps secretions and prevents
Test your knowledge
What is the difference between hypoxia and hypoxaemia?
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Which patients are at risk of hypercapnic respiratory failure?
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What is the risk of over-oxygenation in such patients?
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How would you approach oxygen therapy in patients are at risk of hypercapnic respiratory failure?
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