Low-Flow vs High-Flow Oxygen Systems
Oxygen delivery systems are classified as low-flow (do not meet patient's total inspiratory flow demand, air entrainment dilutes FiO2) or high-flow (meet or exceed inspiratory flow, deliver precise FiO2).
Low-flow systems: - Nasal cannula: 1–6 L/min → FiO2 ~24–44%; each liter adds ~4% FiO2 - Simple face mask: 5–10 L/min → FiO2 ~35–55%; minimum 5 L/min to flush CO2 - Partial rebreather mask: 6–10 L/min → FiO2 ~35–60%; bag should not collapse - Non-rebreather mask (NRB): 10–15 L/min → FiO2 ~60–90%; reservoir bag + one-way valves
High-flow systems: - Venturi mask (air-entrainment mask): precise FiO2 24, 28, 31, 35, 40, 50% — reliable for COPD - HFNC (high-flow nasal cannula): 20–60 L/min heated humidified; FiO2 21–100%
- Nasal cannula: each L/min adds ~4% FiO2 (1L=24%, 2L=28%... 6L=44%)
- Simple mask minimum 5 L/min — to prevent CO2 rebreathing
- NRB: highest FiO2 without intubation (~60–90%); reservoir bag must not collapse
- Venturi mask: precise FiO2, high-flow, preferred for COPD (controlled O2)
- HFNC: 20–60 L/min, provides positive airway pressure, reduces work of breathing
For COPD patients needing precise O2, use a Venturi mask at 28% or 31% — nasal cannula FiO2 is highly variable with breathing pattern changes.