What is the maximum oxygen concentration that can be delivered via a nasal cannula (NC)?

Maximum Oxygen Concentration Deliverable via Nasal Cannula

Standard nasal cannulas can deliver oxygen concentrations (FiO₂) ranging from approximately 24% to 50% at flow rates of 1-6 L/min, while high-flow nasal cannulas can deliver up to 75% oxygen at flow rates of 6-60 L/min. 1, 2

Standard Nasal Cannula Oxygen Delivery

Flow Rate and FiO₂ Relationship

• At 1-4 L/min: Delivers oxygen concentrations equivalent to 24-40% FiO₂ 1
• At 5-6 L/min: Can achieve up to approximately 50% FiO₂ 1, 2

Factors Affecting Delivered Oxygen Concentration

• Patient breathing pattern: Wide variation in delivered FiO₂ due to differences in respiratory rate and tidal volume 1
• Mouth vs. nose breathing: Contrary to expectations, mouth breathing often results in the same or higher oxygen concentration, especially with increased respiratory rates 1
• Individual variation: Large standard deviations (±0.04-0.15) in delivered FiO₂ between patients at the same flow rate 2

Clinical Considerations

• The actual FiO₂ cannot be precisely predicted with standard nasal cannulas 1
• Patient comfort may decrease at flows above 4 L/min due to nasal dryness, though many patients tolerate higher flows 1
• Flows below 5 L/min provide lower oxygen concentrations than a simple face mask 1

High-Flow Nasal Cannula (HFNC) Oxygen Delivery

Flow Rate and FiO₂ Relationship

• At 6-15 L/min: Can deliver mean FiO₂ of 54-75% at rest 2
• At 30-60 L/min: Recommended flow rate for optimal therapeutic benefit 3

Clinical Applications

• Initial recommended flow rate for adults with acute respiratory failure is 60 L/min 3
• Can generate positive airway pressure of approximately 7 cm H₂O at 50 L/min 1
• Provides heated and humidified gas, improving patient comfort and tolerance 3, 4

Practical Application Algorithm

1. For low to medium oxygen requirements:

   • Start with standard nasal cannula at 1-2 L/min (≈24-28% FiO₂)
   • Titrate up to 6 L/min maximum (≈50% FiO₂)
   • Monitor oxygen saturation and adjust flow accordingly

2. For higher oxygen requirements:

   • Switch to HFNC starting at 60 L/min 3
   • Adjust FiO₂ independently to maintain target saturation:
     • 94-98% for patients without hypercapnia risk
     • 88-92% for patients with COPD or risk of hypercapnia 3
   • Maintain minimum flow of 30 L/min to achieve physiological benefits 3

Common Pitfalls and Caveats

• Unpredictable FiO₂: The actual delivered oxygen concentration with standard nasal cannulas varies widely between patients and cannot be precisely predicted 1
• Monitoring requirements: Due to variability in delivered FiO₂, flow rates must be adjusted based on oximetry and, when necessary, blood gas measurements 1
• Patient selection: HFNC should be considered as an alternative to reservoir masks in patients with acute respiratory failure without hypercapnia 3
• COPD patients: A comparison study showed that patients with COPD exacerbation spent more time with oxygen saturation below 90% when using nasal cannulas compared to Venturi masks 1
• Fire risk: Oxygen concentrations exceed 23% only within a few centimeters of the nasal cannula at 2 L/min, but increase with higher flows, creating potential fire hazards near the face 5