title: Desflurane Consumption During Automated Closed-circuit Delivery is Higher Than When a Conventional Anesthesia Machine is Used With a Simple Vaporizer-O₂-N₂O Fresh Gas Flow Sequence.
abstract: BACKGROUND
  The Zeus® (Dräger, Lübeck, Germany), an automated closed-circuit anesthesia machine, uses high fresh gas flows (FGF) to wash-in the circuit and the lungs, and intermittently flushes the system to remove unwanted N₂. We hypothesized this could increase desflurane consumption to such an extent that agent consumption might become higher than with a conventional anesthesia machine (Anesthesia Delivery Unit [ADU®], GE, Helsinki, Finland) used with a previously derived desflurane-O₂-N₂O administration schedule that allows early FGF reduction.
  
  
  METHODS
  Thirty-four ASA PS I or II patients undergoing plastic, urologic, or gynecologic surgery received desflurane in O₂/N₂O. In the ADU group (n = 24), an initial 3 min high FGF of O₂ and N₂O (2 and 4 L.min-1, respectively) was used, followed by 0.3 L.min-1 O2 + 0.4 L.min-1 N₂O. The desflurane vaporizer setting (FD) was 6.5% for the first 15 min, and 5.5% during the next 25 min. In the Zeus group (n = 10), the Zeus® was used in automated closed circuit anesthesia mode with a selected end-expired (FA) desflurane target of 4.6%, and O₂/N₂O as the carrier gases with a target inspired O₂% of 30%. Desflurane FA and consumption during the first 40 min were compared using repeated measures one-way ANOVA.
  
  
  RESULTS
  Age and weight did not differ between the groups (P > 0.05), but patients in the Zeus group were taller (P = 0.04). In the Zeus group, the desflurane FA was lower during the first 3 min (P < 0.05), identical at 4 min (P > 0.05), and slightly higher after 4 min (P < 0.05). Desflurane consumption was higher in the Zeus group at all times, a difference that persisted after correcting for the small difference in FA between the two groups.
  
  
  CONCLUSIONS
  Agent consumption with an automated closed-circuit anesthesia machine is higher than with a conventional anesthesia machine when the latter is used with a specific vaporizer-FGF sequence. Agent consumption during automated delivery might be further reduced by optimizing the algorithm(s) that manages the initial FGF or by tolerating some N₂ in the circuit to minimize the need for intermittent flushing.
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, Onze Lieve Vrouw Hospital, Aalst, Belgium.
authors.forename: Sofie
authors.initials: S
authors.lastname: De Cooman
authors.forename: Nathalie
authors.initials: N
authors.lastname: De Mey
authors.forename: Bram Bc
authors.initials: BB
authors.lastname: Dewulf
authors.forename: Rik
authors.initials: R
authors.lastname: Carette
authors.forename: Thierry
authors.initials: T
authors.lastname: Deloof
authors.forename: Maurice
authors.initials: M
authors.lastname: Sosnowski
authors.forename: Andre M
authors.initials: AM
authors.lastname: De Wolf
authors.forename: Jan Fa
authors.initials: JF
authors.lastname: Hendrickx