At what flow rate of nasal cannula can an FIO2 of approximately 40% be expected?

To achieve an FIO2 (fraction of inspired oxygen) of approximately 40% using nasal cannula, understanding how flow rates correlate with FIO2 is essential. The general rule of thumb is that nasal cannulas provide an FIO2 of about 4% to 5% increase for each liter of oxygen delivered per minute, beginning from room air (which has an FIO2 of about 21%).

Starting from room air, if you use a flow rate of 6 L/min, you can calculate the FIO2:

• At 1 L/min: approximately 25% FIO2

• At 2 L/min: approximately 29% FIO2

• At 3 L/min: approximately 33% FIO2

• At 4 L/min: approximately 37% FIO2

• At 5 L/min: approximately 41% FIO2

• At 6 L/min: approximately 45% FIO2

A flow rate of 6 L/min is the point where the FIO2 approaches the target of 40%. Therefore, it is the most accurate selection when aiming for an FIO2 around 40%.

While a flow rate of 5