What are the various oxygen delivery devices, including low‑flow and high‑flow systems, and their respective flow rates and fraction of inspired oxygen (FiO₂) ranges?

Oxygen Delivery Devices: Systems and Specifications

Nasal cannulae should be your first-line oxygen delivery device for most patients, delivering 1-6 L/min with approximately 3-4% FiO₂ increase per liter, achieving 24-50% FiO₂ range. 1, 2

Low-Flow Oxygen Systems

Nasal Cannulae

• Flow rates: 1-6 L/min 1, 2
• FiO₂ range: Approximately 24-50% (each L/min adds 3-4% to inspired oxygen) 1, 3
• Key advantage: Superior patient comfort, can be worn during meals and speech, lower risk of patient removal 2
• Critical caveat: Actual FiO₂ delivery is highly variable between patients at the same flow rate—individual inspired oxygen concentrations can vary between 24-35% at 2 L/min 1
• Respiratory rate impact: Higher respiratory rates require higher flow rates to maintain the same effective FiO₂ 3, 4
• Mouth breathing: Does not significantly reduce efficiency; may result in same or higher inspired oxygen concentration 3

Simple Face Masks

• Flow rates: 5-10 L/min (never below 5 L/min due to CO₂ rebreathing risk) 2, 3
• FiO₂ range: 40-60% 1, 2, 3
• Major limitation: Less preferred than nasal cannulae due to patient discomfort, cannot be worn during meals 2
• Performance degradation: Variable performance systems like Hudson masks deliver significantly reduced oxygen concentration at high respiratory rates 4

Venturi Masks (Fixed Performance)

• Available concentrations: 24%, 28%, 31%, 35%, 40%, and 60% 2
• Flow rates: Specific to each concentration setting (e.g., 24% requires 89 L/min total gas flow, 28% requires 63 L/min, 31% requires 46 L/min) 3
• Primary indication: Patients requiring precise FiO₂ control, particularly those at risk of hypercapnic respiratory failure (COPD patients) 1, 2
• Special consideration: If respiratory rate exceeds 30 breaths/min, increase flow rate above the minimum specified for the mask 2
• Performance at high respiratory rates: Fixed performance systems delivering 24-40% maintain appropriate oxygen concentrations across respiratory rate ranges, but 60% systems show performance reduction 4

Non-Rebreather Masks (Reservoir Masks)

• Flow rate: 15 L/min initially 2
• FiO₂ range: Up to 90% 5
• Clinical use: Start with 15 L/min for severe hypoxemia, then adjust downward to nasal cannulae or simple face mask once stabilized 2
• Flow rate caveat: Decreasing to 10 L/min significantly reduces both tissue oxygenation and nasopharyngeal FiO₂ 6

High-Flow Oxygen Systems

High-Flow Nasal Cannula (HFNC)

• Flow rates: 30-70 L/min 2
• FiO₂ range: Up to 100% with more predictable delivery 2
• Mechanism: Delivers warmed, humidified oxygen with modest positive airway pressure (CPAP effect) 2
• Primary indications: Acute hypoxemic respiratory failure, post-extubation respiratory support 2
• Airway pressure generated: Low positive expiratory airway pressure (<4 cmH₂O), highly dependent on mouth closure 5
• Not appropriate for: Home oxygen population 1

Boussignac Oxygen Therapy System

• Airway pressure: Generates relevant positive airway pressure during both inspiration and expiration (median 13.9 cmH₂O), independent of mouth position 5
• FiO₂: Approximately 80% (slightly lower than other high-flow systems) 5
• Limitation: Higher discomfort compared to Optiflow and reservoir-bag facemask 5

Specialized Delivery Systems

Oxygen-Conserving Devices

• Mechanism: Deliver oxygen during inspiration only, reducing oxygen waste during expiration 1
• Efficiency: Can reduce oxygen usage by up to 50% 1
• Clinical indication: Patients requiring high flow rates or active outside the home, following ambulatory oxygen assessment 1
• Critical pitfall: Variable ability to maintain SaO₂ levels during exercise; mouth breathers may struggle to trigger them—patients require ambulatory assessment before issuance 1

Trans-Tracheal Oxygen

• Delivery method: Catheter inserted percutaneously between second and third tracheal rings 1
• Advantage: Reduces anatomical dead space, allows lower oxygen levels than nasal cannulae, reduces work of breathing 1
• Serious complications: Catheter displacement, mucous obstruction, infection 1
• Clinical use: Rarely used in home settings, requires dedicated trained team support 1

Clinical Decision Algorithm

For Mild to Moderate Hypoxemia (Target SpO₂ 94-98%)

1. Start with nasal cannulae at 1-4 L/min 2
2. Escalate to higher flow rates (up to 6 L/min) or switch to simple face mask (5-10 L/min) as needed 2
3. Consider HFNC for moderate to severe hypoxemia not responding to conventional therapy 2

For Patients at Risk of Hypercapnic Respiratory Failure (Target SpO₂ 88-92%)

1. Use 24% or 28% Venturi mask or nasal cannulae at low flow rates 2
2. Never exceed target saturation to avoid worsening hypercapnia 2, 7
3. Consider Venturi masks for confused or demented patients where flows might be altered in error 1

For Severe Hypoxemia

1. Start with reservoir mask at 15 L/min 2
2. Adjust downward once stabilized to maintain target saturation 2
3. Prepare for non-invasive ventilation or intubation if inadequate response 2

Key Pitfalls to Avoid

• Never use simple face masks below 5 L/min due to CO₂ rebreathing risk 2
• Do not assume precise FiO₂ with nasal cannulae—titrate based on oximetry measurements and blood gas results 2, 3
• Avoid excessive oxygen in hypercapnic patients—can worsen CO₂ retention 7
• Do not issue oxygen-conserving devices without ambulatory assessment—some patients cannot trigger them effectively 1
• Nasal cannula flow rates above 6 L/min cause discomfort and are not standard practice 7