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Mnemonic

Oxygen Therapy Delivery Devices

A memory aid for fixed and variable performance oxygen devices.

Physiology Respiratory Emergency Respiratory Airway and Ventilation Airway and Breathing Emergencies
Expansion

Variable devices depend on the patient's breathing pattern; fixed devices do not

Expansion

Variable performance - delivered concentration depends on the patient’s minute ventilation and peak inspiratory flow

  • Nasal cannulae: about 24 to 40 per cent at 1 to 4 litres per minute
  • Simple face mask: about 40 to 60 per cent at 5 to 10 litres per minute
  • Non-rebreathe mask with reservoir: about 60 to 80 per cent at 15 litres per minute

Fixed performance - delivered concentration is independent of breathing pattern

  • Venturi mask: colour-coded valves delivering 24, 28, 31, 35, 40 or 60 per cent
  • High flow nasal oxygen: flows of up to 60 litres per minute, which also washes out dead space and generates a small positive pressure

The distinction matters when the concentration must be controlled precisely, as in chronic obstructive pulmonary disease with carbon dioxide retention, where a Venturi device targeting 88 to 92 per cent saturation is preferred.

A patient’s peak inspiratory flow may reach 30 to 60 litres per minute, far exceeding the flow from a simple mask, which is why the rest is entrained room air and the actual concentration is unpredictable.