Oxygen Delivery Devices Guide
From low-flow nasal cannula to high-flow systems and invasive ventilation — a complete reference for selecting and managing oxygen delivery.
Why Oxygen Device Selection Matters
Selecting the correct oxygen delivery device is one of the most fundamental clinical decisions in respiratory care. The goal is to deliver the minimum effective FiO₂ needed to maintain adequate oxygenation while avoiding oxygen toxicity, excessive work of breathing, and patient discomfort.
Oxygen delivery systems are broadly categorized as low-flow (variable performance) or high-flow (fixed performance). Low-flow devices deliver oxygen at a flow rate less than the patient's inspiratory demand, meaning room air is entrained and the actual FiO₂ varies based on the patient's breathing pattern. High-flow devices meet or exceed the patient's inspiratory flow demand, delivering a more consistent FiO₂.
Understanding the approximate FiO₂ range each device can deliver — and its limitations — allows respiratory therapists to make appropriate escalation and de-escalation decisions.
Low-Flow Oxygen Devices
Nasal Cannula
Most common oxygen delivery device. Each additional liter per minute increases FiO₂ by approximately 4%. Above 6 L/min the FiO₂ gains diminish and patient discomfort increases. Best for patients with mild hypoxemia who have a normal to low respiratory rate.
Simple Face Mask
Minimum flow of 5 L/min required to flush exhaled CO₂ from the mask. FiO₂ is variable and depends on patient breathing pattern. Not ideal for patients with high minute ventilation.
Partial Rebreather Mask
Has a reservoir bag that captures the first portion of exhaled breath (rich in O₂) for rebreathing. The bag should remain at least one-third full during inspiration. Used when moderate FiO₂ above simple mask capability is needed.
Non-Rebreather Mask (NRB)
One-way valves prevent exhaled gas from re-entering the reservoir bag. Can deliver the highest FiO₂ of the low-flow masks. Used for moderate-severe hypoxemia, carbon monoxide poisoning, and as a bridge to other interventions. The bag must remain inflated at all times.
High-Flow & Fixed Performance Devices
Venturi Mask (Air-Entrainment Mask)
FiO₂: 24%, 28%, 31%, 35%, 40%, 50%Uses the Bernoulli principle and jet mixing to entrain a precise ratio of room air. Delivers a fixed, reliable FiO₂ regardless of patient breathing pattern. Essential for COPD patients where precise FiO₂ control prevents blunting of hypoxic drive. Color-coded adaptors correspond to specific FiO₂ levels.
High-Flow Nasal Cannula (HFNC)
FiO₂: 21–100%Delivers heated and humidified oxygen at high flow rates exceeding the patient's inspiratory demand. Provides a small amount of positive airway pressure, washes out nasopharyngeal dead space, and significantly reduces work of breathing. Widely used for acute hypoxemic respiratory failure, COVID-19 pneumonia, and post-extubation support.
CPAP (Non-Invasive)
FiO₂: Up to 100%Continuous Positive Airway Pressure via mask maintains alveolar recruitment, increases FRC, and reduces work of breathing. Common indications include OSA, cardiogenic pulmonary edema, and mild respiratory failure. Does not provide inspiratory pressure support — the patient must generate all their own tidal volume.
BiPAP / NIV
FiO₂: Up to 100%Delivers two pressure levels: IPAP (inspiratory) and EPAP (expiratory). The pressure differential between IPAP and EPAP supports each breath. Used for COPD exacerbations, hypercapnic respiratory failure, sleep apnea, and cardiogenic pulmonary edema. Strong evidence base for avoiding intubation in appropriate patients.
Quick FiO₂ Reference Chart
| Device | Flow Rate | Approx. FiO₂ |
|---|---|---|
| Nasal Cannula | 1 L/min | ~24% |
| Nasal Cannula | 2 L/min | ~28% |
| Nasal Cannula | 4 L/min | ~36% |
| Nasal Cannula | 6 L/min | ~44% |
| Simple Mask | 5–10 L/min | ~35–55% |
| Non-Rebreather | 10–15 L/min | ~60–80% |
| Venturi 24% | Per adaptor | 24% (fixed) |
| Venturi 40% | Per adaptor | 40% (fixed) |
| HFNC | 40–60 L/min | Up to ~60%+ |
FiO₂ values are approximate and vary based on patient minute ventilation and breathing pattern.
Frequently Asked Questions
When should HFNC be used instead of a non-rebreather mask?
HFNC is preferred when the patient needs FiO₂ above what a NRB can reliably deliver, when the work of breathing is elevated, or when conventional oxygen therapy is failing. HFNC also provides better comfort and humidification for prolonged use.
Why do COPD patients need precise FiO₂ control?
Some COPD patients with chronic CO₂ retention may rely on hypoxic drive as a ventilatory stimulus. High FiO₂ can reduce this drive, cause V/Q mismatch worsening, and lead to CO₂ retention. Venturi masks and titrated nasal cannula flow allow safe oxygen delivery in this population.
What is the Haldane effect?
The Haldane effect explains why CO₂ retention occurs in some COPD patients on supplemental oxygen. When hemoglobin is fully saturated with O₂, it carries less CO₂, leading to increased dissolved CO₂ and rising PaCO₂ — independent of changes in ventilatory drive.
How is FiO₂ calculated for HFNC?
The actual FiO₂ delivered by HFNC depends on the set FiO₂, the flow rate, and the patient's own inspiratory effort. At very high flows (>40–50 L/min), HFNC closely approximates the set FiO₂. At lower flows, entrainment of room air can dilute the delivered FiO₂.
Summary
- Low-flow devices entrain room air — actual FiO₂ varies with patient breathing pattern.
- Venturi masks provide precise, fixed FiO₂ — critical for COPD management.
- HFNC provides high FiO₂, PEEP effect, and comfort for acute hypoxemic respiratory failure.
- BiPAP provides ventilatory support — preferred for hypercapnic respiratory failure.
- Always titrate oxygen to the minimum needed to achieve target SpO₂ or PaO₂.
- Document the device, flow rate, and patient SpO₂ response for all oxygen therapy.
Bedside References in RTB2
RTB2 offers faster bedside references and advanced tools inside the mobile app — including oxygen device comparisons, FiO₂ estimation tools, and HFNC setup guides.
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