title: Comparison of an infrared anaesthetic agent analyser (Datex-Ohmeda) with refractometry for measurement of isoflurane, sevoflurane and desflurane concentrations.
abstract: OBJECTIVE
  To assess agreement between infrared (IR) analysers and a refractometer for measurements of isoflurane, sevoflurane and desflurane concentrations and to demonstrate the effect of customized calibration of IR analysers.
  
  
  METHODS
  In vitro experiment.
  
  
  METHODS
  Six IR anaesthetic monitors (Datex-Ohmeda) and a single portable refractometer (Riken).
  
  
  METHODS
  Both devices were calibrated following the manufacturer's recommendations. Gas samples were collected at common gas outlets of anaesthesia machines. A range of agent concentrations was produced by stepwise changes in dial settings: isoflurane (0-5% in 0.5% increments), sevoflurane (0-8% in 1% increments), or desflurane (0-18% in 2% increments). Oxygen flow was 2 L minute(-1) . The orders of testing IR analysers, agents and dial settings were randomized. Duplicate measurements were performed at each setting. The entire procedure was repeated 24 hours later. Bland-Altman analysis was performed. Measurements on day-1 were used to yield calibration equations (IR measurements as dependent and refractometry measurements as independent variables), which were used to modify the IR measurements on day-2.
  
  
  RESULTS
  Bias ± limits of agreement for isoflurane, sevoflurane and desflurane were 0.2 ± 0.3, 0.1 ± 0.4 and 0.7 ± 0.9 volume%, respectively. There were significant linear relationships between differences and means for all agents. The IR analysers became less accurate at higher gas concentrations. After customized calibration, the bias became almost zero and the limits of agreement became narrower.
  
  
  CONCLUSIONS
  If similar IR analysers are used in research studies, they need to be calibrated against a reference method using the agent in question at multiple calibration points overlapping the range of interest.
authors: Anaesthesiology and perioperative Intensive-Care Medicine, Department for Companion Animals and Horses, University of Veterinary Medicine, Vienna, Austria.
authors: Andrea S
authors: AS
authors: Rudolff
authors: Yves P S
authors: YP
authors: Moens
authors: Bernd
authors: B
authors: Driessen
authors: Tamas D
authors: TD
authors: Ambrisko
mesh_terms: D018685:Anesthetics, Inhalation / Q000737:chemistry*; D000818:Animals; D000077335:Desflurane; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000737:chemistry*; D008738:Methyl Ethers / Q000737:chemistry*; D016343:Monitoring, Intraoperative; D012031:Refractometry / Q000295:instrumentation*; D000077149:Sevoflurane; D013055:Spectrophotometry, Infrared / Q000295:instrumentation*
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane
keywords: anaesthetics; calibration; infrared gas analysis; monitoring; refractometry