Oxygen Delivery Devices: Selection Based on FiO₂ Requirements and Clinical Status
For most patients requiring supplemental oxygen, start with nasal cannulae at 1-6 L/min (providing 24-50% FiO₂), escalating to Venturi masks for precise control in hypercapnic-risk patients, reservoir masks for critically ill patients needing high FiO₂, and high-flow nasal cannula (HFNC) for acute hypoxemic respiratory failure. 1, 2, 3
Low-Flow Oxygen Delivery (FiO₂ 24-50%)
Nasal Cannulae: First-Line for Most Patients
- Nasal cannulae are the preferred initial device for medium-concentration oxygen therapy due to superior comfort, tolerance during meals and speech, and equivalent clinical efficacy. 1, 2
- Flow rates of 1-6 L/min deliver approximately 24-50% FiO₂, with each liter adding 3-4% to inspired oxygen concentration. 1, 2
- Actual FiO₂ varies significantly between individuals (24-35% at 2 L/min) due to differences in respiratory rate and breathing pattern. 1, 2
- Target oxygen saturation of 94-98% in patients without hypercapnic risk. 2, 3
Key advantages over face masks: 1, 2
- No claustrophobic sensation
- Not removed for eating or speaking
- No risk of CO₂ rebreathing
- Lower inspiratory resistance
- Less expensive
Limitations to recognize: 1
- May cause nasal irritation above 4 L/min
- Ineffective if nose severely congested
- Actual FiO₂ cannot be precisely predicted
Medium-Concentration Oxygen (FiO₂ 40-60%)
Simple Face Masks: Alternative When Nasal Route Fails
- Flow rates of 5-10 L/min deliver 40-60% FiO₂. 1, 3, 4
- Never use below 5 L/min due to dangerous CO₂ rebreathing risk. 1, 2, 4
- Less preferred than nasal cannulae due to patient discomfort and need for removal during meals. 1, 4
- Effectiveness greatly reduced if not properly positioned and sealed. 3, 4
Precise FiO₂ Control (24-60%)
Venturi Masks: For Hypercapnic-Risk Patients
- Venturi masks are mandatory for patients requiring accurate FiO₂ delivery, particularly those at risk of hypercapnic respiratory failure such as COPD patients. 1, 2, 3, 4
- Deliver precise concentrations: 24%, 28%, 31%, 35%, 40%, and 60% when used with manufacturer-specified flow rates. 1, 2, 3, 4
- Target oxygen saturation of 88-92% in hypercapnic-risk patients. 2, 3, 4
- Preferred for confused or cognitively impaired patients to prevent inadvertent flow-rate errors. 1, 2
Critical adjustment: If respiratory rate exceeds 30 breaths/min, increase flow rate above the minimum specified for the Venturi mask to maintain accurate FiO₂. 1, 2
High-Concentration Oxygen (FiO₂ 60-90%)
Reservoir/Non-Rebreather Masks: For Critically Ill Patients
- Flow rate of 15 L/min delivers 60-90% FiO₂. 2, 3, 4
- Indicated for severe hypoxemia in trauma and emergency situations. 4
- Start with reservoir mask at 15 L/min for severe hypoxemia, then titrate down to nasal cannulae or simple face mask once stabilized. 2
- Contraindicated in patients at risk of CO₂ retention. 4
High-Flow Nasal Cannula (HFNC): Advanced Oxygen Therapy
Indications and Mechanisms
- HFNC delivers 30-70 L/min of warmed, humidified oxygen, providing more predictable FiO₂, modest positive airway pressure (CPAP effect of ~7 cmH₂O at 50 L/min), and superior patient comfort. 1, 2, 5, 6
- Reduces anatomical dead space and work of breathing. 5, 6
Primary indications: 1, 2, 5, 6
- Acute hypoxemic respiratory failure
- Post-extubation respiratory support
- Preoxygenation before intubation
- Immunocompromised patients
- "Do not intubate" status patients
- Reduces reintubation risk compared to conventional oxygen (4.9% vs 12.2%, p=0.04)
- Better tolerated and more comfortable than face masks
- Associated with better oxygenation and lower respiratory rate
Important caveat: HFNC is not appropriate for routine home oxygen therapy—its use is limited to acute care settings. 1, 2
Clinical Decision Algorithm
Step 1: Assess Hypercapnic Risk
High risk (COPD, obesity hypoventilation, neuromuscular disease):
- Start with Venturi mask at 24% or 28%
- Target SpO₂ 88-92%
- Monitor with arterial blood gas if available 1, 2, 3, 4
Low risk (pneumonia, pulmonary edema, trauma):
Step 2: Escalate Based on Response
Mild hypoxemia (SpO₂ 88-93%):
- Nasal cannulae 1-4 L/min 2
Moderate hypoxemia (SpO₂ 85-87%):
- Nasal cannulae 4-6 L/min or simple face mask 5-10 L/min 2
Severe hypoxemia (SpO₂ <85%):
- Reservoir mask 15 L/min initially, then titrate down 2
- Consider HFNC if available and patient not hypercapnic 1, 2, 5
Step 3: Consider HFNC for Persistent Hypoxemia
HFNC should be considered when: 5, 6, 7
- Reservoir mask fails to maintain adequate oxygenation
- Patient cannot tolerate face mask
- Acute hypoxemic respiratory failure without hypercapnia
- Post-extubation with high oxygen requirements
HFNC provides better balance between oxygenation and comfort compared to NIV and Venturi mask in hypoxemic respiratory failure. 7
Specialized Delivery Systems
Oxygen-Conserving Devices
- Deliver oxygen only during inspiration, reducing consumption by up to 50%. 1, 2
- Indicated for ambulatory patients requiring high flow rates or active outside home. 2
- Require formal ambulatory oxygen assessment before prescription due to variable ability to maintain SpO₂ during exercise and failure in mouth-breathing patients. 1, 2
Trans-Tracheal Oxygen
- Rarely used due to serious complications (catheter displacement, mucus obstruction, infection). 2
- Requires dedicated, trained multidisciplinary team. 2
Critical Pitfalls to Avoid
Never use simple face masks below 5 L/min—this causes dangerous CO₂ rebreathing. 1, 2, 4
Do not use high-flow oxygen without controlled delivery in hypercapnic-risk patients—this worsens hypercapnia. 2, 3
Mask effectiveness is greatly reduced if not properly positioned—ensure proper seal. 3, 4
Do not assume nasal cannulae deliver consistent FiO₂—adjust based on oximetry and blood gas measurements. 1
Recognize HFNC failure early—prepare for intubation if patient deteriorates despite HFNC. 2