With thanks to Dr Horsley, Infectious Diseases registrar at North Manchester General Hospital
Nasal cannulae:
- 1-6 L/min
- Deliver ~22-44%
- Higher flow rates (>4 L/min) generally intolerable
Simple face mask:
- 2-10 L/min
- Deliver ~35-60% (between 5 and 10 L/min)
- Uncontrolled and variable oxygen concentration
- Ideally > ~6 L/min to prevent CO2 accumulation
Reservoir mask:
- Ideally ~12-15 L – reservoir must be inflated and doesn’t fully collapse during inspiration
- Deliver ~85-90% at 15 L/min
- Uncontrolled and variable concentration
Venturi mask: *reserve only for patients at risk of Type II respiratory failure*
- Fixed flow rates of 24-60% depending on valve used (colour coded)
- Based on the Bernoulli principle
- Gas flow through narrowed section increases in velocity but decreases in pressure, drawing in air in a predictable ratio
- “Fixed” oxygen concentrations
