A standard nasal cannula is not recommended for flows greater than 6 L/min due to ___________.

• A. Increased humidity
• B. Increased noise
• C. Mask leakage
• D. Patient discomfort

Answer: (D)

The key idea is how tolerable the delivery method is for the patient. A standard nasal cannula delivers oxygen through nasal prongs, and at higher flows the gas can be forceful and, without humidification, drying. This drying and irritation of the nasal mucosa leads to discomfort, burning, and a strong dislike of the sensation, making it difficult for patients to keep the cannula in place. Because comfort and tolerance drop off around 6 L/min, this is the practical upper limit for a standard nasal cannula. If higher oxygen flows or higher FiO2 are needed, clinicians switch to humidified/high-flow systems or a different interface to avoid that discomfort. Increased humidity would actually help reduce dryness, so it isn’t the reason for the limit. Leakage around the prongs and other factors are secondary to the main issue: patient discomfort at higher flows.