Oxygen therapy

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

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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Oxygen masks

Nasal cannula

Hudson simple face mask

Venturi (air entrapment) mask

Types of Venturi Mask

Non-rebreather mask

High flow nasal oxygen (e.g. Optiflow)

Non-invasive ventilation

CPAP (continuous positive airway pressure)

BiPAP (bi-level positive airway pressure)

Invasive ventilation

Invasive ventilation

General points

Test your knowledge

Try some OSCE stations that require oxygen therapy

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