Expansion
From nasal cannulae to non-rebreathe and Venturi masks
Expansion
| Device | Flow | Approximate FiO2 |
|---|---|---|
| Nasal cannulae | 1 to 6 l/min | 24 to 40 per cent, variable |
| Simple face mask | 5 to 10 l/min | 40 to 60 per cent, variable |
| Venturi mask | Per valve | Fixed: 24, 28, 31, 35, 40, 60 per cent |
| Non-rebreathe with reservoir | 15 l/min | 60 to 90 per cent |
| High flow nasal oxygen | up to 60 l/min | Up to 100 per cent, with some PEEP |
| Bag valve mask | 15 l/min | Near 100 per cent with reservoir |
Variable versus fixed performance: with variable devices the inspired concentration depends on the patient’s own inspiratory flow, so a breathless patient entrains more room air and receives less. Venturi masks deliver a fixed concentration regardless, which is why they are used when precision matters.
Target saturations
- 94 to 98 per cent for most acutely unwell patients
- 88 to 92 per cent where there is a risk of hypercapnic respiratory failure, typically chronic obstructive pulmonary disease, obesity hypoventilation, neuromuscular disease and chest wall deformity, pending blood gases
Never withhold oxygen from a hypoxic patient for fear of carbon dioxide retention; the correct action is to give controlled oxygen with a Venturi mask, check gases, and titrate. Hypoxia kills faster than hypercapnia.
Oxygen is a drug and must be prescribed, with the target range specified.