The air we breathe contains a specific amount of oxygen. In medical settings, understanding the precise concentration of oxygen a person is inhaling is important, especially when supplemental oxygen is needed. This measurement, known as the Fraction of Inspired Oxygen (FiO2), represents the percentage of oxygen in the gas mixture entering the lungs.
FiO2 in Room Air
The air surrounding us, room air, contains approximately 21% oxygen. This 21% FiO2 serves as the baseline. Establishing this standard allows healthcare professionals to determine how much additional oxygen is necessary when a person requires respiratory assistance.
Determining FiO2 with Oxygen Delivery Devices
When supplemental oxygen is administered, the FiO2 inhaled by an individual changes from room air. Various oxygen delivery devices are designed to provide different concentrations. The actual FiO2 delivered can depend on factors such as the patient’s breathing pattern and flow rate.
A nasal cannula, a device with two prongs inserted into the nostrils, is commonly used for low-flow oxygen delivery. For every liter per minute (L/min) of oxygen supplied, the FiO2 increases by approximately 4% above the ambient 21%. For example, 1 L/min provides an FiO2 of about 24%, and 2 L/min delivers around 28%. Individual factors can influence the exact FiO2 received.
Simple face masks cover both the nose and mouth, delivering oxygen at higher flow rates than a nasal cannula. These masks operate at flow rates between 5 and 10 L/min. The FiO2 delivered by a simple face mask ranges from 35% to 60%. A minimum flow rate of 5 L/min is recommended to prevent the rebreathing of exhaled carbon dioxide.
For individuals requiring higher oxygen concentrations, a non-rebreather mask is used. This mask features a reservoir bag and one-way valves that prevent exhaled air from mixing with the oxygen in the bag. Non-rebreather masks can deliver a high FiO2, ranging from 60% to 90% at flow rates of 8 to 15 L/min. The patient primarily inhales oxygen directly from the reservoir, offering a concentrated supply.
Venturi masks provide a more precise and consistent FiO2. These masks work by mixing a specific amount of oxygen with room air through various color-coded adapters or jets. Each adapter is designed to deliver a fixed FiO2, ranging from 24% to 60%. This precise control is useful for individuals who require a specific and stable oxygen concentration.
Why Understanding FiO2 Matters
Understanding FiO2 is important because it impacts patient outcomes by ensuring adequate oxygen delivery to the body’s tissues. Too little oxygen, a condition known as hypoxemia, can lead to cell damage and organ dysfunction. Conversely, receiving too much oxygen, or hyperoxia, can have adverse effects. Prolonged exposure to high levels of oxygen can cause oxidative damage to cells and tissues, particularly in the lungs. Healthcare professionals adjust the FiO2 delivered to patients to maintain appropriate oxygen saturation levels while minimizing these risks.