Infrared absorption spectroscopy is commonly used during routine anesthesia of veterinary patients to measure concentrations of inhaled anesthetic agents. There may also be a need to use these monitors for measuring anesthetic agent concentrations during clinical research projects (eg, minimum alveolar concentration–related studies) or for testing the accuracy of vaporizers. The accuracy of IR absorption spectroscopy may be adversely affected by multiple factors, such as the presence of other molecules in the sample with overlapping IR absorption spectra (eg, methane or propellant of medical aerosols),1,2 pressure-broadening effect,3 calibration problems,4,5 and artifacts.6
Refractometry, gas chromatography, and mass spectrometry are commonly used as reference methods with which the accuracy of other instruments is compared. The superior accuracy of refractometry is established, and it has been recommended to be used as the gold standard for testing vaporizers and anesthetic gas monitors.7,8 The accuracy of an IAGM (similar to the monitor used in the study of this report) has been determined for halothane and isoflurane but not for sevoflurane and desflurane.9 The purpose of the study reported here was to assess agreement between anesthetic agent concentrations measured by use of an IAGM and refractometry. The IAGM was a commercially available device used in our veterinary hospital, and its accuracy for measurement of isoflurane, sevoflurane, desflurane, and N2O concentrations was compared with that of a portable refractometer.
Infrared anesthetic gas monitor
POET IQ, model 602-6B, Criticare Systems Inc, Waukesha, Wis.
Riken 1802D, Riken Keiki Co Ltd, Tokyo, Japan.
Attane, Minrad Inc, Bethlehem, Pa.
SevoFlo, Abbott Laboratories, North Chicago, Ill.
Suprane, Baxter International Inc, Deerfield, Ill.
Nitrous oxide USP, Airgas East Inc, Salem, NJ.
Microsoft Excel 2002, Microsoft Corp, Redmond, Wash.
Narkovet Deluxe, North American Dräger, Telford, Pa.
Vapor 19.1, North American Dräger, Telford, Pa.
Sigma Delta, Penlon Ltd, Abingdon, Oxfordshire, England.
TEC-6, Datex-Ohmeda Inc, Madison, Wis.
Dujardin CL, Gootjes P, Moens Y. Isoflurane measurement error using short wavelength infrared techniques in horses: influence of fresh gas flow and pre-anaesthetic food deprivation. Vet Anaesth Analg 2005; 32: 101–106.
Levin PD, Levin D, Avidan A. Medical aerosol propellant interference with infrared anaesthetic gas monitors. Br J Anaesth 2004; 92: 865–869.
Bergman NA, Rackow H, Frumin MJ. The collision broadening effect of nitrous oxide upon infrared analysis of carbon dioxide during anesthesia. Anesthesiology 1958; 19: 19–26.
Christensen PL, Nielsen J, Kann T. Methods to produce calibration mixtures for anesthetic gas monitors and how to perform volumetric calculations on anesthetic gases. J Clin Monit 1992; 8: 279–284.
Nielsen J, Kann T, Moller JT. Evaluation of three transportable multigas anesthetic monitors: the Bruel & Kjaer Anesthetic Gas Monitor 1304, the Datex Capnomac Ultima, and the Nellcor N-2500. J Clin Monit 1993; 9: 91–98.
Dorsch JA, Dorsch SE. Gas monitoring. In: Zinner S, ed. Understanding anesthesia equipment. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 1999;679–753.
Allison JM, Gregory RS, Birch KP, et al. Determination of anaesthetic agent concentration by refractometry. Br J Anaesth 1995; 74: 85–88.
Wallroth CF, Gippert KL, Ryschka M, et al. Refractive indices for volatile anesthetic gases: equipment and method for calibrating vaporizers and monitors. J Clin Monit 1995; 11: 168–174.
Walder B, Lauber R, Zbinden AM. Accuracy and cross-sensitivity of 10 different anesthetic gas monitors. J Clin Monit 1993; 9: 364–373.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307–310.
Merin RG, Bernard JM, Doursout MF, et al. Comparison of the effects of isoflurane and desflurane on cardiovascular dynamics and regional blood flow in the chronically instrumented dog. Anesthesiology 1991; 74: 568–574.
Nyktari VG, Papaioannou AA, Prinianakis G, et al. Effect of the physical properties of isoflurane, sevoflurane, and desflurane on pulmonary resistance in a laboratory lung model. Anesthesiology 2006; 104: 1202–1207.
Tirel O, Wodey E, Harris R, et al. The impact of age on bispectral index values and EEG bispectrum during anaesthesia with desflurane and halothane in children. Br J Anaesth 2006; 96: 480–485.
Steffey EP. Inhalation anesthetics. In: Thurmon JC, Tranquilli WJ, Benson JB, eds. Lumb & Jones' veterinary anesthesia. 3rd ed. Baltimore: Williams & Wilkins, 1996;297–329.
Sivasankar B. Instrumental methods of analysis. In: Sivasankar B, ed. Engineering chemistry. New Delhi: Tata McGraw-Hill, 2008;288–342.
Scheeren TW, Krossa M, Merilainen P, et al. Error in measurement of oxygen and carbon dioxide concentrations by the DeltatracII metabolic monitor in the presence of desflurane. Br J Anaesth 1998; 80: 521–524.
Ferrell WR, Payne MG, Garrett WR. Resonance broadening and shifting of spectral lines in xenon and krypton. Phys Rev A 1987; 36:81.