Nasal oxygen delivery works primarily by increasing the concentration of oxygen in the air you breathe, thereby improving oxygen uptake into your bloodstream.
Here's a breakdown of how different nasal oxygen delivery methods work:
Low-Flow Nasal Cannula
- Mechanism: A low-flow nasal cannula delivers a controlled flow of oxygen directly into the nostrils. This oxygen mixes with the air you inhale from the environment (room air).
- Oxygen Concentration: The fraction of inspired oxygen (FiO2) – the percentage of oxygen you're breathing – depends on the oxygen flow rate and your breathing pattern. Typical flow rates range from 1 to 6 liters per minute (LPM), which can provide an FiO2 of approximately 24% to 44%. Room air is about 21% oxygen.
- How it Helps: By increasing the oxygen concentration of inhaled air, the nasal cannula helps to raise the partial pressure of oxygen in your alveoli (tiny air sacs in the lungs). This, in turn, enhances the diffusion of oxygen from the alveoli into your blood.
High-Flow Nasal Cannula (HFNC)
HFNC offers more than just increased oxygen concentration; it also provides several other benefits:
- Mechanism: HFNC delivers a heated and humidified mixture of air and oxygen at high flow rates (typically 20-60 LPM) through nasal prongs.
- Reduced Dead Space: The high flow rate flushes out the upper airway (nasopharynx) and replaces it with oxygen-rich gas. This reduces the anatomical dead space, the volume of air inhaled that doesn't participate in gas exchange.
- Improved Airway Pressure: While not true positive pressure ventilation, HFNC does generate a small amount of positive airway pressure. This pressure can help to keep the alveoli open, improving gas exchange.
- Constant FiO2: The high flow rates ensure a more consistent and predictable FiO2 compared to low-flow systems, as the patient's inspiratory flow has less impact on the delivered oxygen concentration.
- Humidification: HFNC delivers heated and humidified gas, which is more comfortable for the patient and helps to prevent drying of the nasal mucosa and airway secretions. This is especially important at high flow rates.
- Reduced Work of Breathing: By providing a high flow of oxygen-rich gas, HFNC can reduce the work of breathing, making it easier for patients to breathe. The reference’s mention of dilating airways with positive pressure is an older theory; the more accepted mechanisms involve the ones described above.
In summary, nasal oxygen, whether low-flow or high-flow, works by increasing the amount of oxygen you inhale, improving the oxygen saturation in your blood and easing the work of breathing. High-flow nasal cannula provides additional benefits beyond increased oxygen concentration, such as reduced dead space, improved airway pressure, constant FiO2 and humidification.
