A low flow nasal cannula is a medical device that delivers supplemental oxygen to individuals who have difficulty maintaining adequate oxygen levels.
How a Low Flow Nasal Cannula Works
A low flow nasal cannula functions by delivering a controlled flow of oxygen directly into a person’s nostrils. The device consists of a thin, flexible tube with two small prongs that rest just inside the nasal passages. This tubing connects to an oxygen source, such as a portable oxygen concentrator or a wall outlet in a medical facility.
Oxygen flows from the source through the tube and into the nostrils at a specific rate, measured in liters per minute (LPM). For low flow systems, this rate usually ranges from 1 to 6 LPM. The oxygen delivered through the cannula mixes with the room air the person breathes in, meaning the total concentration of oxygen inhaled, known as the Fraction of Inspired Oxygen (FiO2), varies.
Room air contains approximately 21% oxygen. For every additional liter per minute of oxygen delivered by a low flow nasal cannula, the FiO2 generally increases by about 4%. For example, 1 LPM can provide an FiO2 of around 24-25%, while 6 LPM can increase it to approximately 44-45%. The actual FiO2 a person receives depends on their breathing pattern, including their respiratory rate and tidal volume, which influence how much room air is entrained with the supplemental oxygen.
Medical Conditions Requiring Supplemental Oxygen
Supplemental oxygen delivered via a low flow nasal cannula is often prescribed for individuals with conditions that impair their body’s ability to absorb enough oxygen from ambient air. These conditions can be acute, meaning they occur suddenly, or chronic, persisting over a long period. One common chronic condition is Chronic Obstructive Pulmonary Disease (COPD), which includes emphysema and chronic bronchitis, where damaged airways and air sacs reduce effective gas exchange.
Other conditions include pneumonia, an infection that inflames the air sacs and can fill them with fluid, and congestive heart failure, where the heart’s reduced pumping efficiency can lead to fluid buildup in the lungs. Respiratory failure, sleep apnea, and cystic fibrosis can also necessitate oxygen supplementation. In these instances, providing extra oxygen helps compensate for the body’s reduced capacity to oxygenate the blood, thereby supporting cellular function and reducing strain on the heart and lungs. Patients recovering from surgery or those with severe cases of illnesses like COVID-19 may also require temporary oxygen support.
Proper Use and Care
Proper placement of a low flow nasal cannula is important for effective oxygen delivery and patient comfort. To wear the device, insert the two prongs gently into the nostrils, ensuring they curve slightly inward towards the back of the nose. The tubing then extends along the cheeks and loops over each ear, similar to eyeglasses.
After looping over the ears, the two tubes meet under the chin, where a slider can be adjusted to secure the cannula snugly. The fit should be comfortable, allowing enough space to fit two fingers between the tubing and the chin, without causing pressure or irritation. Regularly check the skin behind the ears and at the nostrils for any signs of redness or soreness, and consider using a water-based lotion or soft gauze pads to protect these areas.
Low flow nasal cannulas typically do not provide humidified oxygen, which can lead to nasal dryness and irritation. Attaching a humidifier bottle to the oxygen source can help prevent these discomforts by adding moisture. The cannula should be cleaned regularly: wipe the prongs and tubing daily with an alcohol swab, or wash weekly with mild soap and warm water, allowing them to air dry. Replace the entire cannula tubing approximately every two to four weeks, or sooner if it becomes stiff, discolored, or damaged, to maintain hygiene and effectiveness.