A 27-year-old woman received from the emergency department is on a nasal cannula at 5 L/min. Approximately what FiO2 is this patient receiving?

a. 28%
b. 32%
c. 35%
d. 40%

ANS: D
Estimating the FiO2 provided by low-flow systems: For patients with a normal rate and depth of breathing, each liter per minute of nasal O2 increases the FiO2 approximately 4%. For example, a patient using a nasal cannula at 4 L/min has an estimated FiO2 of approximately 37% (21 + 16).