title: Preoxygenation with tidal volume and deep breathing techniques: the impact of duration of breathing and fresh gas flow.
abstract: Various techniques of "preoxygenation" before anesthetic induction have been 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 compared the effectiveness of these techniques, assessed extending deep breathing beyond 1 min, or investigated the influence of fresh gas flow (FGF) in the same subjects using a circle absorber system. In 24 healthy adult volunteers breathing oxygen from a circle absorber system by tight-fitting mask, we 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 measured 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/min FGF, respectively. ETO2 values of > or =90% were attained between 3 and 4 min. Four DB/0.5 min increased ETO2 to 75%, 77%, and 80% at 5, 7, and 10 L/min FGF. Eight DB/min resulted in ETO2 values of 82% and 87% at 7 and 10 L/min, respectively. Extending deep breathing to 1.5 and 2 min with 10 L/min FGF increased ETO2 by > or =90%, although a decrease in ETCo(2) was noted. We concluded that TVB/3-5 min was effective in achieving maximal "preoxygenation" whereas 4 DB/0.5 min resulted in submaximal "preoxygenation," and thus should be used only when time is limited. 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 "preoxygenation" when extended to 1.5 or 2 min, and only when high (10 L/min) FGF is used.
  
  
  CONCLUSIONS
  Using a circle absorber system, normal breathing of oxygen for 3-5 min achieves optimal oxygenation of the lungs; whereas 4 deep breaths in 30 s does not. However, extending deep breathing to 1.5-2 min and using a high flow of oxygen improves oxygenation of the lungs to the same degree as normal breathing for 3-5 min. This may have important implications for patient safety.
authors.affiliation: Department of Anesthesiology, Illinois Masonic Medical Center, 836 W. Wellington Avenue, Chicago, IL 60657, USA.
authors.forename: U
authors.initials: U
authors.lastname: Nimmagadda
authors.forename: S D
authors.initials: SD
authors.lastname: Chiravuri
authors.forename: M R
authors.initials: MR
authors.lastname: Salem
authors.forename: N J
authors.initials: NJ
authors.lastname: Joseph
authors.forename: Y
authors.initials: Y
authors.lastname: Wafai
authors.forename: G J
authors.initials: GJ
authors.lastname: Crystal
authors.forename: M I
authors.initials: MI
authors.lastname: El-Orbany
mesh_terms: D000328:Adult; D000764:Anesthesia, Closed-Circuit; D002245:Carbon Dioxide / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000008:administration & dosage* / Q000502:physiology; D012119:Respiration; D013990:Tidal Volume; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen