Air-oxygen mixtures in circle systems

Jan F.A. Hendrickx, Sofie De Cooman, Dirk M. Vandeput, Jan Van Alphen, José Coddens, Thierry Deloof, Andre M. De Wolf*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Study Objective: To determine the effect of different air-O 2 mixtures and fresh gas flows (FGF) on the relationship between the delivered (F DelO 2) and inspired O 2 fraction (FIO 2) in a circle system. Study Design: Randomized clinical study. Setting: Large teaching hospital. Patients: 160 ASA physical status I, II, and III patients undergoing a variety of cardiovascular procedures with general endotracheal anesthesia. Interventions: 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 DelO 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 DelO 2. Measurements and Main Results: With any air-O 2 mixture with a FGF ≤ 2 L/min, FIO 2 became lower than F DelO 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 DelO 2 with FGF ≤ 2 L/min. The relative proportion of O 2 in the FGF has to be increased accordingly.

Original languageEnglish (US)
Pages (from-to)461-464
Number of pages4
JournalJournal of Clinical Anesthesia
Issue number6
StatePublished - 2001


  • Air, oxygen
  • Anesthesia techniques
  • Circle system
  • Low-flow anesthesia
  • Patient safety

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine


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