Oxygen Therapy and Delivery Devices
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Direct answer
Oxygen therapy corrects hypoxaemia by raising the fraction of inspired oxygen (FiO2) that reaches the lungs, and the delivery device determines how far it rises. Nasal prongs give low, variable concentrations, whereas venturi masks, reservoir masks and high-flow nasal cannula deliver higher or more controlled levels. Oxygen should be titrated to a target SpO2, because excess oxygen, especially in preterm neonates, causes harm.
What you must remember
- Nasal prongs: each litre per minute adds roughly 4 per cent to the FiO2 above room air, so 1 to 4 litres per minute gives about 24 to 40 per cent.
- Simple face mask: delivers about 35 to 60 per cent at 5 to 10 litres per minute, and the flow must stay at or above about 5 litres per minute to prevent rebreathing.
- Venturi mask: fixed FiO2 set by the entrainment valve, usually between 24 and 60 per cent, and the best choice when carbon dioxide retention is a concern.
- Non-rebreathing mask: a reservoir bag with one-way valves gives high concentrations, often 60 to 80 per cent, but only while the bag stays inflated.
- High-flow nasal cannula: heated, humidified gas at up to about 2 litres per kg per minute in infants, which reduces work of breathing in bronchiolitis and after extubation.
- Saturation targets: preterm neonates are usually aimed at 90 to 95 per cent, and term infants and children at 94 to 98 per cent, per standard guidance.
- Oxygen toxicity: prolonged hyperoxia in preterm infants causes retinopathy of prematurity and contributes to bronchopulmonary dysplasia.
Matching the device to flow and FiO2
Each device has a flow range that sets the oxygen concentration the child actually receives. Exam questions usually ask you to match the device to the clinical problem, so learn the ranges together.
| Device | Typical flow | Approximate FiO2 | Best use |
|---|---|---|---|
| Nasal prongs | 0.5 to 4 L/min | 24 to 40 per cent | Mild hypoxaemia, home oxygen |
| Simple face mask | 5 to 10 L/min | 35 to 60 per cent | Moderate hypoxaemia |
| Venturi mask | Set by the valve | 24 to 60 per cent, fixed | Controlled FiO2, carbon dioxide retention |
| Non-rebreathing mask | 10 to 15 L/min | 60 to 80 per cent | Severe acute hypoxaemia, shock |
| High-flow nasal cannula | Up to about 2 L/kg/min | Adjustable, up to 100 per cent | Bronchiolitis, post-extubation support |
The table answers which-device questions quickly. Reservoir and high-flow devices deliver the most oxygen, but a venturi mask wins whenever accuracy matters more than concentration.
Where the exam tries to catch you
Most oxygen questions turn on the device, the flow and the target.
- Trap: using a non-rebreathing mask for a child who retains carbon dioxide, as in chronic lung disease. Correct: a venturi mask delivers a fixed, controlled FiO2 and avoids overshooting the oxygen concentration.
- Trap: giving 100 per cent oxygen to every sick neonate. Correct: preterm neonates are titrated to a target SpO2 because hyperoxia risks retinopathy of prematurity.
- Trap: assuming a simple face mask works at 2 litres per minute. Correct: below about 5 litres per minute the mask cannot flush exhaled carbon dioxide, so the child rebreathes it.
Frequently asked questions
Which oxygen device gives the most precise FiO2?
The venturi mask gives the most precise FiO2, because its valve fixes the air-to-oxygen ratio. It is preferred when a child retains carbon dioxide and needs a controlled concentration. Nasal prongs and reservoir masks give less predictable levels.
What SpO2 target is used for a preterm neonate?
Preterm neonates are generally aimed at an SpO2 of 90 to 95 per cent under standard neonatal guidance. Term infants and children are usually targeted at 94 to 98 per cent. The local protocol should guide the final target.
What is the minimum flow for a simple face mask?
A simple face mask needs a flow of at least about 5 litres per minute to flush exhaled carbon dioxide from the mask. Lower flows let carbon dioxide build up, so the child rebreathes it. Nasal prongs suit children who need only low concentrations.
Why is high-flow nasal cannula used in bronchiolitis?
High-flow nasal cannula delivers heated, humidified oxygen at high flow, which reduces work of breathing and provides some distending airway pressure. It is used in bronchiolitis and after extubation when standard devices are not enough.
What complication follows prolonged oxygen in preterm infants?
Prolonged hyperoxia in preterm infants causes retinopathy of prematurity and contributes to bronchopulmonary dysplasia. Careful SpO2 targeting limits both risks.