Oxygen Delivery Devices Comparison
A detailed comparison of oxygen delivery devices — FiO₂ ranges, flow rates, and clinical selection criteria to help respiratory therapists choose the right device for every patient.
Written for respiratory therapists, students, and clinicians.
Overview: Low-Flow vs High-Flow Oxygen Systems
Oxygen delivery devices are broadly classified as low-flow or high-flow systems. The distinction is not about the flow rate set on the flowmeter, but about whether the device supplies the patient's total inspiratory flow demand.
Low-flow systems (nasal cannula, simple mask, partial rebreather) do not supply all of the patient's inspiratory flow. Room air is entrained around or through the device to meet demand, which means the actual delivered FiO₂ varies depending on the patient's respiratory pattern — tidal volume and rate. These devices are variable-performance systems.
High-flow systems (Venturi masks, HFNC) deliver gas at rates that meet or exceed the patient's peak inspiratory flow, providing a more consistent and predictable FiO₂ regardless of breathing pattern. These are fixed-performance systems.
Device-by-Device Comparison
Nasal Cannula (NC)
Flow Rate
1–6 L/min
Approx FiO₂
24–44%
Key Note
~4% per L/min above 21%
Advantages: Most comfortable, allows eating/talking, simple to apply
Limitations: FiO₂ highly variable with breathing pattern; dries nasal mucosa at >4 L/min without humidification
Best used for: Mild hypoxemia, chronic home oxygen, post-extubation maintenance
Simple Face Mask
Flow Rate
5–10 L/min
Approx FiO₂
35–60%
Key Note
Minimum 5 L/min to flush CO₂
Advantages: Higher FiO₂ than NC; simple design
Limitations: Must be removed for eating; masks speech; less comfortable than NC; unreliable FiO₂
Best used for: Moderate hypoxemia when NC is insufficient but high-flow not available
Partial Rebreather Mask (PRB)
Flow Rate
6–10 L/min
Approx FiO₂
40–70%
Key Note
Reservoir bag must remain inflated
Advantages: Higher FiO₂ than simple mask; reservoir adds O₂
Limitations: Must keep bag from collapsing; CO₂ rebreathing if flow too low
Best used for: Moderate-to-severe hypoxemia when NRB not required
Non-Rebreather Mask (NRB)
Flow Rate
10–15 L/min
Approx FiO₂
60–90%
Key Note
Reservoir must stay inflated; one-way valves prevent rebreathing
Advantages: Highest FiO₂ of low-flow devices; widely available
Limitations: Uncomfortable; claustrophobic; poor seal = entrainment lowers FiO₂
Best used for: Acute severe hypoxemia, CO poisoning, bridge to HFNC or NIV
Venturi Mask (Air-Entrainment)
Flow Rate
Varies by color/adapter
Approx FiO₂
24–60% (precise)
Key Note
Fixed FiO₂ regardless of patient's breathing pattern
Advantages: Precise FiO₂ delivery — true fixed-performance system
Limitations: Multiple components; flow must match adapter specification; uncomfortable
Best used for: COPD and hypercapnic patients needing controlled, precise FiO₂
High-Flow Nasal Cannula (HFNC)
Flow Rate
20–60 L/min
Approx FiO₂
21–100%
Key Note
Heated, humidified; washes out nasopharyngeal dead space
Advantages: High comfort; precise FiO₂; generates slight PEEP effect; reduces work of breathing
Limitations: Requires specialized equipment; may delay intubation if deteriorating
Best used for: Hypoxemic respiratory failure, post-extubation, COPD (carefully titrated)
Clinical Selection Algorithm
Device selection should be based on the patient's SpO₂ target, respiratory pattern, risk of CO₂ retention, and clinical trajectory:
Mild hypoxemia (SpO₂ 90–94%)
Nasal cannula 1–4 L/min; titrate to SpO₂ ≥92%
Moderate hypoxemia, not responding to NC
Simple mask or partial rebreather at 6–10 L/min
Severe acute hypoxemia
Non-rebreather 10–15 L/min → escalate to HFNC if not improving
COPD with risk of hypercapnia
Venturi mask at 24–28% FiO₂; target SpO₂ 88–92%
Hypoxemic respiratory failure (non-COPD)
HFNC 40–60 L/min; FiO₂ titrated to SpO₂ ≥94%
Acute hypercapnic failure with mild acidosis
BiPAP with EPAP 4–5, IPAP 10–12; titrate
Frequently Asked Questions
Why is it important to use controlled FiO₂ in COPD?
Patients with chronic hypercapnia who rely on hypoxic drive for respiratory stimulus may reduce ventilation if given excessive oxygen. Targeting SpO₂88–92% in known COPD patients avoids suppressing respiratory drive and worsening hypercapnia and respiratory acidosis. The Venturi mask is preferred because it delivers a precisely controlled FiO₂ regardless of breathing pattern.
What FiO₂ does a nasal cannula actually deliver?
The FiO₂ from a nasal cannula is highly variable and depends on the patient's tidal volume and respiratory rate. As a rough approximation, each 1 L/min of flow adds approximately 3–4% FiO₂ above room air (21%). At 2 L/min: ~28–29%; at 4 L/min: ~36–37%; at 6 L/min: ~44%. Patients breathing rapidly and shallowly will entrain more room air, reducing actual FiO₂.
How does HFNC generate a PEEP effect?
HFNC delivers gas at flows (20–60 L/min) that typically exceed the patient's inspiratory demand. This continuous high flow maintains a slight positive pressure in the nasopharynx during expiration, acting like a low-level PEEP (estimated 1–3 cmH₂O). It also flushes the nasopharyngeal dead space with fresh high-FiO₂ gas, improving oxygenation efficiency.
Summary
- Low-flow devices have variable FiO₂; high-flow devices (Venturi, HFNC) provide precise FiO₂
- Always match the device to the patient's oxygenation need and CO₂ retention risk
- COPD patients with hypercapnia should receive controlled FiO₂ — Venturi mask or HFNC titrated to SpO₂ 88–92%
- HFNC provides high FiO₂, comfort, and slight PEEP — first-line for hypoxemic respiratory failure without hypercapnia
Explore More with RTB2
Explore faster bedside tools and advanced references in the RTB2 mobile app — including oxygen device selection guides, FiO₂ estimation tools, and clinical decision aids.
Related articles