title: Air-oxygen mixtures in circle systems.
abstract: OBJECTIVE
  To determine the effect of different air-O(2) mixtures and fresh gas flows (FGF) on the relationship between the delivered (F(Del)O(2)) and inspired O(2) fraction (FIO(2)) in a circle system.
  
  
  METHODS
  Randomized clinical study.
  
  
  METHODS
  Large teaching hospital.
  
  
  METHODS
  160 ASA physical status I, II, and III patients undergoing a variety of cardiovascular procedures with general endotracheal anesthesia.
  
  
  METHODS
  160 patients were randomly assigned to one of 20 groups (n = 8 each), depending on the combination of total FGF (0.5, 1, 2, 4, or 8 L/min) and air-O(2) mixture used (ratios of 4/1, 3/2, 2/3, or 1/4), corresponding to a F(Del)O(2) of 0.37, 0.53, 0.68, and 0.84. For each combination of FGF and air-O(2) mixture, FIO(2) after equilibration was compared with F(Del)O(2).
  
  
  RESULTS
  With any air-O(2) mixture with a FGF < or = 2 L/min, FIO(2) became lower than F(Del)O(2). Because FIO(2) decreased below 0.25 after 13 and 26 minutes in the first two patients of the 4/1 0.5 L/min air-O(2) group, this study limb was terminated.
  
  
  CONCLUSIONS
  When using air-O(2) mixtures in a circle system, FIO(2) becomes lower than the F(Del)O(2) with FGF < or = 2 L/min. The relative proportion of O(2) in the FGF has to be increased accordingly.
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, Onze Lieve Vrouwziekenhuis, Aalst, Belgium.
authors.forename: J F
authors.initials: JF
authors.lastname: Hendrickx
authors.forename: S
authors.initials: S
authors.lastname: De Cooman
authors.forename: D M
authors.initials: DM
authors.lastname: Vandeput
authors.forename: J
authors.initials: J
authors.lastname: Van Alphen
authors.forename: J
authors.initials: J
authors.lastname: Coddens
authors.forename: T
authors.initials: T
authors.lastname: Deloof
authors.forename: A M
authors.initials: AM
authors.lastname: De Wolf
mesh_terms: D000388:Air; D000758:Anesthesia / Q000379:methods*; D006801:Humans; D010100:Oxygen / Q000008:administration & dosage*
chemical_list: D010100:Oxygen