Oxygen Delivery Devices
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Direct answer
Oxygen delivery devices are classified as low-flow (variable FiO2 that depends on the patient's breathing) and high-flow or fixed-performance (precise FiO2). A nasal cannula at 1–6 L/min delivers roughly 24–44 per cent oxygen, a simple face mask at 5–8 L/min about 40–60 per cent, a non-rebreathing mask at 10–15 L/min up to about 90 per cent, and a Venturi mask delivers precise low concentrations of about 24–50 per cent. The choice follows the target saturation, not the device's maximum.
What you must remember
- Nasal cannula: 1–6 L/min, about 24–44 per cent FiO2 (each litre adds roughly 4 per cent); comfortable for long-term use, but dries the mucosa, so humidification is advised above about 4 L/min.
- Simple face mask: 5–8 L/min (never below 5, or exhaled carbon dioxide is rebreathed), about 40–60 per cent FiO2 for short-term moderate hypoxaemia.
- Non-rebreathing mask: 10–15 L/min with a reservoir bag and one-way valves, the highest concentration among masks; keep the reservoir two-thirds inflated.
- Venturi (air-entrainment) mask: fixed, precise FiO2 set by colour-coded adapters — the choice when exact concentration matters, especially in carbon dioxide retainers.
- Non-invasive ventilation (CPAP, BiPAP) and high-flow nasal cannula are advanced systems for selected patients, not ordinary masks.
- In COPD patients at risk of hypercapnia, titrate oxygen to a target saturation of about 88–92 per cent; in most acutely ill adults the target is 94–98 per cent.
- Nursing care: check flow rate, tubing and mask fit each shift; give skin care at the ears and nasal bridge; change cannulas and humidifier water per policy; display "no smoking" signage because oxygen supports combustion.
Common confusion
Percentages get swapped in examinations, so remember the logic: the cannula entrains the most room air and gives the least oxygen, while the non-rebreather with its reservoir gives the most. Students also confuse the Venturi mask's role — chosen for accuracy, not high concentration, its classic indication being the COPD patient needing controlled oxygen. A practical trap is the simple mask run below 5 L/min: the FiO2 does not simply fall; the patient rebreathes carbon dioxide from the mask dead space.
Exam-focused takeaway
Learn the flow ranges and approximate FiO2 for each device, the 88–92 per cent target in COPD, and the rule of never withholding oxygen from a dangerously hypoxaemic patient while awaiting a prescription. Safety questions test humidification thresholds, fire precautions and skin care under masks. A typical stem describes a drowsy COPD patient on a high-flow device with rising carbon dioxide and expects a switch to controlled delivery with a Venturi mask.
Frequently asked questions
Which oxygen device delivers the most precise FiO2?
The Venturi or air-entrainment mask, which mixes oxygen with entrained room air through colour-coded adapters to give fixed concentrations.
What flow and concentration suit a nasal cannula?
1–6 L/min delivering approximately 24–44 per cent oxygen, with humidification usually advised above 4 L/min.
Why must a simple face mask run at least 5 L/min?
At lower flows the patient rebreathes exhaled carbon dioxide retained in the mask dead space.
What oxygen target is used in COPD patients?
About 88–92 per cent saturation, since higher concentrations may worsen carbon dioxide retention — but never leave a dangerously hypoxaemic patient without oxygen.
What safety precautions accompany oxygen therapy?
No smoking or open flames nearby, no oil-based products near the device, secure cylinder handling, and regular checks of flow, tubing and skin under masks.