Which preoxygenation FiO2 target is described as being used to fill the lungs before induction?

• A. 100% FiO2
• B. 50% FiO2
• C. 21% FiO2
• D. 80% FiO2

Answer: (A)

Preoxygenation aims to fill the lungs with oxygen to create an oxygen reservoir that buys time during the apneic period after induction. The most effective way to maximize that reservoir is to use the highest FiO2 available, which drives nitrogen washout from the functional residual capacity and raises alveolar oxygen tension to its maximum. This denitrogenation expands the time before desaturation occurs if breathing stops for any reason during induction. Lower FiO2 levels leave nitrogen in the lungs and provide a smaller oxygen store, so they don’t offer the same protection. In practice, you perform preoxygenation with the highest possible oxygen concentration to optimize the lung’s oxygen reserve before induction.