Preoxygenation with tidal volume and deep breathing techniques: The impactof duration of breathing and fresh gas flow

Various techniques of "preoxygenation" before anesthetic induction have bee n advocated, including tidal volume breathing (TVB) for 3-5 min, four deep breaths (DB) in 0.5 min, and eight DB in 1 min. However, no study has compa red the effectiveness of these techniques, assessed extending deep breathin g beyond 1 min, or investigated the influence of fresh gas flow (FGF) in th e same subjects using a circle absorber system. In 24 healthy adult volunte ers breathing oxygen from a circle absorber system by tight-fitting mask, w e compared TVB/5 min and deep breathing at a rate of 4 DB/0.5 min for 2 min at 5, 7, and 10 L/min FGF. Inspired and end-tidal respiratory gases were m easured at 0.5-min intervals. During TVB, end-tidal oxygen (ETO2) increased rapidly and plateaued by 2.5 min at 86%, 88%, and 88% with 5, 7 and 10 L/m in FGF, respectively. ETO2 values of greater than or equal to 90% were atta ined between 3 and 4 min. Four DB/0.5 min increased ETO2 to 75%, 77%, and 8 0% at 5, 7, and 10 L/min FGF. Eight DB/min resulted in ETO2 values of 82% a nd 87% at 7 and 10 L/min, respectively. Extending deep breathing to 1.5 and 2 min with 10 L/min FGF increased ET2, by greater than or equal to 90% alt hough a decrease in ETco2, was noted. We concluded that TVB/3-5 min was eff ective in achieving maximal "preoxygenation" whereas 4 DB/0.5 min resulted in submaximal "preoxygenation," and thus should be used only when time is l imited. Increasing FGF from 5 to 10 L/min does not enhance "preoxygenation" with either TVB or 4 DB/0.5 min. Deep breathing yields maximal "preoxygena tion" when extended to 1.5 or 2 min, and only when high (10 L/min) FGF is u sed.