What is ideal time for Preoxygenation?

Preoxygenation entails replacement of the nitrogen volume of the lung (as much as 95% of FRC) with oxygen in order to provide a reservoir for diffusion into the alveolar capillary blood after the onset of apnea. To provide effective preoxygenation, a methodical approach is necessary. The impoance of preoxygenation with a tight-fitting mask should be explained to the patient beforehand. Once preoxygenation is initiated, EtO2 and FIO2 values should be monitored closely. If the EtO2 value does not increase as expected, the anesthesia provider may have to hold the mask with both hands and/or replace the mask with a better-fitting one. Whenever possible, the induction should not sta until the EtO2 value approximates or exceeds 90%.. the ideal time period is 3 minutes.