The Fraction of Inspired Oxygen (FiO2) refers to the concentration of oxygen in the air a person inhales. It is expressed as a percentage or a decimal, with room air having an FiO2 of 21% (or 0.21). Understanding FiO2 is fundamental in respiratory care, as it directly influences the amount of oxygen available for gas exchange. Healthcare professionals use FiO2 as a significant parameter for oxygen support.
Understanding FiO2
Normal atmospheric air contains 21% oxygen. When supplemental oxygen is provided, it increases the percentage of oxygen in the gas mixture a person breathes. This elevated concentration directly impacts the amount of oxygen that reaches the alveoli, where gas exchange occurs.
The goal of increasing FiO2 is to improve blood oxygen levels for individuals not getting enough oxygen from room air. The effectiveness of this increased oxygen concentration depends on how well the lungs facilitate gas exchange. Factors like the oxygen delivery device and breathing pattern influence the actual FiO2 delivered and its impact on oxygenation.
Estimating FiO2 for Common Devices
Estimating FiO2 for different oxygen delivery devices involves understanding how each device mixes supplemental oxygen with room air. Precise measurement can be complex, but general estimations are used in clinical practice.
A nasal cannula delivers oxygen through two prongs placed in the nostrils. For every liter per minute (L/min) of oxygen flow, FiO2 is estimated to increase by approximately 4% above room air (21%). For example, 1 L/min delivers an estimated FiO2 of 25%, 2 L/min delivers 29%, and up to about 44% at 6 L/min. Actual FiO2 can vary based on a person’s breathing rate and depth.
A simple face mask covers the nose and mouth, delivering FiO2 from 35% to 60% at 5 to 10 L/min. A minimum flow rate of 5 L/min is important to prevent rebreathing exhaled carbon dioxide. The final oxygen concentration can vary depending on how much room air mixes with the oxygen, influenced by mask fit and individual breathing.
The non-rebreather mask is designed to deliver a high oxygen concentration, typically 60% to 90%. This mask has a reservoir bag that fills with oxygen and one-way valves that prevent exhaled air from entering the bag and minimize room air entrainment. To ensure the highest FiO2, the reservoir bag should remain inflated, usually requiring 10 to 15 L/min flow rates.
Venturi masks, also known as air-entrainment masks, deliver a specific, fixed FiO2 regardless of breathing pattern. They use a jet mixing principle where oxygen flows through a narrow opening, entraining precise room air to achieve a set concentration. Color-coded adapters correspond to specific FiO2 levels, each requiring specific oxygen flow rates. This precise control makes them suitable when consistent FiO2 is important, such as for certain respiratory conditions.
The Clinical Significance of FiO2
Accurately managing FiO2 ensures patients receive appropriate oxygen support. Too little oxygen (hypoxemia) can lead to insufficient supply to tissues, potentially causing cell and organ damage. Conversely, too much oxygen (hyperoxia) can have harmful effects, leading to oxygen toxicity.
Oxygen toxicity can manifest as damage to the lungs, especially with prolonged exposure to high FiO2 levels. Healthcare professionals monitor oxygen saturation and adjust FiO2 to maintain optimal oxygenation while minimizing risks. Precise FiO2 titration supports patient well-being and prevents complications from oxygen imbalances.