Preoxygenation is recommended in order to prevent hypoxemia with hypoventilation or apnea during induction of anesthesia. The purpose of this study was to determine the duration of preoxygenation required to achieve an end-tidal oxygen fraction(FE'O₂) of 0.9 in children and adults.

In 24 healthy children and adults breathing 100% oxygen, end tidal oxygen and carbon dioxide concentration have been measured at 15 seconds interval from the start of liter per minute. The gas sampling line of the Capnomac II(Datex, Helsinki, Finland) was placed in the nasal cavity.

The study showed that all children attained an FE'O₂ of 0.9 within 75s of preoxygenation, but adults had not reached an FE'O₂ of 0.9 within 180s.

More oxygen wash-in would be expected in children. We suggested that at least 3 min of preoxygenation should be performed before intravenous induction of anesthesia in children.