When is oxygen delivered through a nasal cannula least beneficial?

Oxygen delivered through a nasal cannula is least beneficial for a patient who breathes through the mouth because the primary function of the nasal cannula is to deliver supplemental oxygen directly into the nasal passages. When a patient is breathing through their mouth, the effectiveness of the nasal cannula diminishes significantly, as the oxygen is not being inhaled through the intended route. This can lead to inadequate oxygenation and may require a different method of oxygen delivery, such as a face mask, that is better suited for mouth breathers.

In contrast, the other scenarios, such as a patient with a respiratory infection, facial injuries, or a history of asthma, while they may pose challenges for oxygen delivery, do not completely negate the benefit of using a nasal cannula. For example, patients with respiratory infections may still benefit from the supplemental oxygen provided that they can use the nasal cannula appropriately. Similarly, patients with facial injuries may need additional considerations, but the cannula can still be used if the nasal passages are unobstructed. For patients with asthma, they may still effectively use a nasal cannula as part of their management during an episode.