Gas chromatographic determination of volatile anaesthetic agents in blood. Part 1. Preparation of standard gas mixtures of volatile anaesthetic agents

Measurement of Anesthetics in Blood Using a Conventional Infrared Clinical Gas Analyzer

BACKGROUND

Measurement of the partial pressure of volatile anesthetics in blood is usually done using a "headspace equilibration" method with gas chromatography. However, it is not often performed in clinical studies because of the technical, equipment, and logistic requirements. To improve the accessibility of this measurement, we tested the use of a common infrared clinical gas analyzer, the Datex-Ohmeda Capnomac, for this purpose.

METHODS

After characterization of the linearity of the device in measuring the volatile anesthetic concentration in the presence of nitrous oxide, carbon dioxide, and water vapor, blood was tonometered with known concentrations of sevoflurane (actual value between 0.5% and 5.0%) in oxygen and oxygen/nitrous oxide mixtures, as well as mixtures of isoflurane and desflurane in oxygen.

RESULTS

Mean bias (standard deviation) overall for sevoflurane in oxygen relative to the tonometered reference partial pressure was -4.5 (4.8%) of the actual concentration. This was not altered significantly by measurement in 40% oxygen/60% nitrous oxide. For isoflurane and desflurane it was -3.9 (3.3%) and -4.6 (3.8%), respectively, of the actual concentration.

CONCLUSIONS

The accuracy and precision of measurement of volatile anesthetic gas partial pressures in blood by a double headspace equilibration technique, using a clinical infrared gas analyzer, were comparable to that achieved by previous studies using gas chromatography.

Sensitive determination of four general anaesthetics in human whole blood by capillary gas chromatography with cryogenic oven trapping

Four general anaesthetics, sevoflurane, isoflurane, enflurane and halothane, in human whole blood, have been found measurable with very high sensitivity by capillary gas chromatography-flame ionization detection (GC-FID) with cryogenic oven trapping upon injection of headspace (HS) vapor sample. To a 7-ml vial, containing 0.48 ml of distilled water and 20 microl of internal standard solution (5 microg), a 0.5-ml of whole blood sample spiked with or without anaesthetics, was added, and the mixture was heated at 55 degrees C for 15 min. A measure of 10 ml HS vapor was injected into the GC in the splitless mode at -40 degrees C oven temperature, which was programmed up to 250 degrees C. All four peaks were clearly separated; no impurity peaks were found among their peaks. Their extraction efficiencies were about 10%. The calibration curves showed good linearity in the range of 0.5-20 microg/ml; their detection limits were 10-100 ng/ml, which are almost comparable to those by previous reports. The coefficients of intra-day and day-to-day variations were 6.5-9.8 and 7.3-17.2%, respectively. Isoflurane or enflurane was also measured from whole blood samples in which three volunteers inhaled each compound.

Quantitative determination of isoflurane enantiomers in blood samples during and after surgery via headspace gas chromatography-mass spectrometry

The quantitative analysis of the chiral volatile anesthetic isoflurane (1) for biomedical applications by means of enantioselective gas chromatography (mass sensitive detector, selected ion monitoring) was studied. Two methods for the quantification of the enantiomers in blood samples drawn during and after narcosis were compared. Either the isomeric enflurane (2) was selected as an internal standard or a single enantiomer of 1 was used for the standard addition method, an approach referred to as 'enantiomer labeling'. Concentrations up to 0.3 micromol/l of the single enantiomers could be differentiated two days after anesthesia. The presented data imply that the body clearance for (+)-(S)-1 and (-)-(R)-1 proceeds to a measurable degree of enantioselectivity.

The quantitative analysis of inhalational anaesthetics in forensic samples by gas chromatography/mass spectrometry/selected ion monitoring

The quantitative analysis of volatile anaesthetics for biomedical applications by means of gas chromatograph/mass spectrometry/selected ion monitoring (GC/MS/SIM) was studied. Xenon gas was selected as an internal standard for the assay by adding to a closed system, because of its stability and inactivity. In the assay of inhalational anaesthetics, isoflurane and nitrous oxide (laughing gas), in forensic samples (serum and cerebrospinal fluid), the calibration of the anaesthetic was linear from 0.12 to 12 nmol/mL in isoflurane and from 30 to 300 nmol/mL in nitrous oxide. Our results suggest that this new method is suitable for the quantitative analysis of inhalational anaesthetics in the biomedical field.