[Laughing gas as the principle substance in assessing occupational exposure to inhalation anesthetics]

In the Federal Republic of Germany limits for the chronic exposure to nitrous oxide and volatile anaesthetics have been prescribed by legislation. According to the technical rules for the handling of hazardous substances TRGS 402 it is legal to measure a single substance in a mixture of hazards, unless the behaviour of all substances is known. Studies about corresponding concentrations of nitrous oxide and volatile anaesthetics in anaesthetic working areas have not yet been carried out.

During one working week each the concentrations of nitrous oxide, enflurane and desflurane were measured by infrared spectrometry in a working area equipped with air condition and in a non-ventilated operating theatre. Corresponding concentrations of nitrous oxide were measured from the same gas samples.

Statistical calculations showed linear correlations of the enflurane and nitrous oxide concentrations in all anaesthetic areas. No linear regression was found between the desflurane and nitrous oxide concentrations. In the working area where desflurane anaesthesias were carried out, significantly higher concentrations of nitrous oxide were observed. Nevertheless the Chi2-test showed no significant differences in the distribution of categorised measurement values.

Although it is not possible to calculate desflurane concentrations from the nitrous oxide concentrations, measurement of nitrous oxide as leading substance is a valid procedure to assess the exposure of the anaesthesiology workplace to nitrous oxide and volatile anaesthetics. Significant higher nitrous oxide concentrations during desflurane anaesthesia result from early extubation of patients expiring higher concentrations of nitrous oxide.