The nasal cannula is a common medical device used to deliver supplemental oxygen to patients experiencing difficulty breathing or low blood oxygen levels. This non-invasive respiratory support helps increase the concentration of oxygen a person inhales, often necessary for conditions like chronic obstructive pulmonary disease (COPD), pneumonia, or heart failure. The device is a simple, lightweight system that connects to an oxygen source, allowing for greater mobility and comfort compared to a full face mask.
Resolving the Terminology Confusion
The terms “nasal cannula” and “nasal prongs” are often used interchangeably, but they refer to different parts of the overall oxygen delivery system. A nasal cannula is the complete medical device, consisting of the tubing, the portion that secures around the head, and the elements that sit inside the nose. The nasal prongs are simply the small, twin projections at the end of the cannula that directly insert into the nostrils. In clinical practice, the word “cannula” describes the entire unit used to administer the oxygen, whether it is a low-flow or a high-flow system. The prongs are the specific interface that channels the oxygen into the patient’s upper airway. Clarifying this distinction confirms that a nasal prong is a component of a nasal cannula.
The Anatomy and Mechanism of Standard Nasal Cannulas
The standard nasal cannula is designed for low-flow oxygen delivery, typically administering oxygen at a rate between 1 and 6 liters per minute (L/min). This low-flow system has a simple physical structure: a long, thin tube that splits into two smaller tubes leading to the nasal prongs. The tubing is secured by looping it over the ears and under the chin, ensuring the prongs remain comfortably seated just inside the nares.
The mechanism of oxygen delivery is considered passive because the flow rate is relatively low and does not fully meet the patient’s peak inspiratory demand. When the patient inhales, the delivered oxygen is supplemented or diluted by the surrounding room air drawn in through the nose and mouth. This mixing means the precise fraction of inspired oxygen (FiO2) the patient receives can vary depending on their breathing rate and pattern. Flow rates above 4 to 6 L/min can irritate and dry out the nasal mucosa, potentially causing discomfort or nosebleeds.
Beyond Standard Flow: High-Flow Variations and Applications
A significant variant is the High-Flow Nasal Cannula (HFNC), which operates on a fundamentally different principle than the standard low-flow device. HFNC systems deliver flow rates up to 60 L/min, substantially higher than the 6 L/min limit of conventional cannulas. This high velocity of gas flow is capable of meeting or even exceeding the patient’s inspiratory flow rate, ensuring a much more precise and consistent oxygen concentration.
The system is distinct because it actively heats the air/oxygen mixture to body temperature (around 37 degrees Celsius) and humidifies it to near 100% relative humidity. Conditioning the high flow of gas prevents the nasal passages from drying out, which is a major limitation of standard low-flow oxygen therapy. This conditioning significantly improves patient comfort and helps maintain the natural function of the respiratory tract, including mucociliary clearance.
High-flow therapy also provides a small amount of positive airway pressure, which can help keep the airways open and reduces the patient’s work of breathing. By continuously flushing the dead space in the nasopharynx, the HFNC system ensures that the patient inhales less carbon dioxide that was just exhaled, improving the overall efficiency of gas exchange. These physiological effects make HFNC a powerful tool for patients with acute hypoxemic respiratory failure, post-surgical breathing issues, or as an alternative to non-invasive ventilation.