Refractive indices for volatile anesthetic gases: Equipment and method for calibrating vaporizers and monitors

Abstract

If refractometry replaced calibration gases in cylinders, as a calibration standard, manufacturers might avoid errors that now occur because calibration gases manufactured by numerous companies seem to differ. We propose that our values serve as an interim database.

Comparison of an infrared anaesthetic agent analyser (Datex-Ohmeda) with refractometry for measurement of isoflurane, sevoflurane and desflurane concentrations

“…The agent specific refractive indices can be determined using known gas standards but can also be obtained from scientific publications (Wallroth et al. ). Obtaining and using high quality calibration standards containing multiple concentrations of each agent are expensive, labour intensive and may have certain inaccuracies (Christensen et al.…”

“…; Wallroth et al. ). A portable digital refractometer (Riken Optical Gas Indicator, model FI‐21, Type 55; Riken Keiki Co., Ltd., Japan) was used in this study.…”

Accuracy of ten isoflurane vaporisers in current clinical use

“…Refractometry has been proposed as superior to infra-red gas analysis for the purpose of calibrating vaporisers and monitors [29]; however, it is not readily available in clinical areas. Manufacturers' guidelines on vaporiser calibration [30] suggest the use of a commercially available infra-red gas analyser calibrated with reference gas, the method used by Nielsen et al [27] and Johnston et al [1].…”

Factitious reading by gas monitor

“…The refractive index of en-, iso- and sevo-flurane is overlapping (1,540.4, 1,563.3 and 1,538.3, respectively). [3] Thus, they require complex methods of discrimination along with advanced mathematical techniques to identify and measure them.…”