title: Effects of gas composition on the delivered tidal volume of the Avance Carestation.
abstract: BACKGROUND
  Measurements with various flowmeters are affected by changes in gas mixture density. The Avance Carestation incorporates ventilator feedback controlled by a built-in flowmeter with a variable orifice sensor. We hypothesised that changes in the composition of delivered gas may cause changes in the delivered tidal volume by affecting the flow measurement unless appropriate corrections are made.
  
  
  METHODS
  We used 100 % O2, 40 % O2 in N2 and 40 % O2 in N2O as carrier gases with/without sevoflurane and desflurane. We measured delivered tidal volume using the FlowAnalyzer™ PF 300 calibrated with the corresponding gas mixtures during volume control ventilation with 500-ml tidal volume using the Avance Carestation connected to a test lung.
  
  
  RESULTS
  Change of carrier gas and addition of sevoflurane and desflurane significantly altered delivered tidal volume. Desflurane 6 % reduced delivered tidal volume by 7.6, 3.6 and 16 % of the pre-set volume at 100 % O2, 40 % O2 in N2 and 40 % O2 in N2O, respectively. Importantly, the Carestation panel indicator did not register these changes in measured expired tidal volume. Ratios of delivered tidal volume to 500 ml correlated inversely with the square root of the delivered gas density.
  
  
  CONCLUSIONS
  These results support our hypothesis and suggest that changing gas composition may alter delivered tidal volume of anesthesia machines with built-in ventilators that are feedback-controlled by uncorrected flowmeters due to changes in gas mixture density.
authors.affiliation: Division of Medical Engineering, Mizonokuchi Hospital, Teikyo University School of Medicine, Kawasaki, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Miyaji
authors.affiliation: Division of Medical Engineering, Mizonokuchi Hospital, Teikyo University School of Medicine, Kawasaki, Japan.
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Fukakura
authors.affiliation: Department of Anesthesiology, Saitama International Medical Center, Saitama Medical School, Saitama, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Usuda
authors.affiliation: Department of Anesthesiology, Mizonokuchi Hospital, Teikyo University School of Medicine, 3-8-3 Mizonokuchi, Takatsu-ku, Kawasaki, 213-8507, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Maruyama
authors.affiliation: Department of Anesthesiology, Mizonokuchi Hospital, Teikyo University School of Medicine, 3-8-3 Mizonokuchi, Takatsu-ku, Kawasaki, 213-8507, Japan.
authors.forename: Go
authors.initials: G
authors.lastname: Hirabayashi
authors.affiliation: Department of Anesthesiology, Mizonokuchi Hospital, Teikyo University School of Medicine, 3-8-3 Mizonokuchi, Takatsu-ku, Kawasaki, 213-8507, Japan.
authors.forename: Rieko
authors.initials: R
authors.lastname: Yamada
authors.affiliation: Department of Anesthesiology, Mizonokuchi Hospital, Teikyo University School of Medicine, 3-8-3 Mizonokuchi, Takatsu-ku, Kawasaki, 213-8507, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Akihisa
authors.affiliation: Department of Anesthesiology, Mizonokuchi Hospital, Teikyo University School of Medicine, 3-8-3 Mizonokuchi, Takatsu-ku, Kawasaki, 213-8507, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Nishioka
authors.affiliation: Department of Anesthesiology, Mizonokuchi Hospital, Teikyo University School of Medicine, 3-8-3 Mizonokuchi, Takatsu-ku, Kawasaki, 213-8507, Japan. psdelico06@yahoo.co.jp.
authors.forename: Tomio
authors.initials: T
authors.lastname: Andoh
mesh_terms: D000077335:Desflurane; D005740:Gases / Q000737:chemistry*; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000031:analogs & derivatives*; D008738:Methyl Ethers / Q000008:administration & dosage*; D000077149:Sevoflurane; D013990:Tidal Volume / Q000502:physiology*; D012122:Ventilators, Mechanical
chemical_list: D005740:Gases; D008738:Methyl Ethers; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane
keywords: Anesthesia machine; Flowmeter; Gas density; Ventilation