What is the maximum flow rate through a nasal cannula (NC)?

Maximum Flow Rate Through Nasal Cannula

Low-flow nasal cannula is defined as oxygen delivered at ≤6 L/min, while high-flow nasal cannula is defined as oxygen delivered at >6 L/min. 1

Standard (Low-Flow) Nasal Cannula

The maximum flow rate for standard nasal cannula is 6 L/min, which delivers approximately 24-50% FiO2 depending on the patient's breathing pattern. 1, 2

Flow Rate Guidelines:

• 1-4 L/min: Delivers approximately 24-40% FiO2 2
• 5 L/min: Delivers approximately 40% FiO2 2
• 6 L/min: Maximum for standard nasal cannula, delivers approximately 50% FiO2 2

Clinical Context:

• Flow rates above 6 L/min are not recommended for standard nasal cannula due to inadequate humidification, which causes nasal irritation, dryness, and patient discomfort 2, 3
• The British Thoracic Society specifically recommends supplemental oxygen by nasal cannulae at 2-6 L/min when used alongside air-driven nebulizers for patients requiring controlled oxygen therapy 1
• Flow rates above 4 L/min can cause discomfort and nasal dryness in some patients, though many tolerate it well 2

High-Flow Nasal Cannula (HFNC)

For high-flow nasal cannula systems, flow rates can reach 60-70 L/min or higher, providing warmed, humidified oxygen with more predictable FiO2 delivery. 2, 4

HFNC Flow Rate Guidelines:

• Initial settings: 35-60 L/min for adults, titrated to patient comfort and respiratory effort 4
• Typical therapeutic range: 30-70 L/min 5
• Optimal physiological benefit: 50-60 L/min provides greater PEEP effect and dead space washout 4
• Post-extubation support: 35-50 L/min typically sufficient 4

Key Distinction:

The critical difference is that HFNC systems incorporate heated humidification, which allows for the delivery of much higher flow rates without causing mucosal drying or patient discomfort that limits standard nasal cannula to 6 L/min. 3, 6

Clinical Decision Algorithm

When to Use Standard Nasal Cannula (≤6 L/min):

• Mild to moderate hypoxemia requiring 24-50% FiO2 2
• Patients requiring medium-concentration oxygen therapy 1
• Situations where patient comfort during meals and speech is important 2
• Cost-effective oxygen delivery for stable patients 2

When to Escalate to HFNC (>6 L/min):

• Moderate to severe hypoxemia requiring higher FiO2 or flow rates 5
• Acute hypoxemic respiratory failure 2
• Post-extubation respiratory support 4
• When standard nasal cannula at 6 L/min fails to maintain target oxygen saturation 5

Common Pitfalls to Avoid

• Never exceed 6 L/min on standard nasal cannula without heated humidification, as this causes significant patient discomfort and mucosal injury 2, 3
• Do not confuse standard nasal cannula with HFNC systems—they are fundamentally different devices with different maximum flow capabilities 1
• Remember that FiO2 delivered by standard nasal cannula varies significantly between patients based on breathing pattern, making it unsuitable when precise FiO2 calculation is required 2
• For patients at risk of hypercapnic respiratory failure (e.g., COPD), target lower oxygen saturations (88-92%) regardless of delivery method 1, 4