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.

Our results indicate that calibration gases containing volatile anesthetic vapors appear to be stable when stored in suitable cylinders. Aluminum cylinders sealed with a stop-cock seem to be suitable. In contrast, mini bottles seem to be less stable, probably due to the sealing construction. The difference of up to 0.09 vol% between our measurement of vapor concentration and the manufacturer's certified concentration may result from adsorption on surfaces in the cylinders after preparation or may reflect differences in calibration technique.

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Numerous medical applications of closed-loop control have been developed over the past 40 years. For the patient breathing system, appropriate sensors are available. Feedback controllers have been developed and tested. Gas and vapor delivery devices seem ready for use. With the sensors, controllers, and delivery devices developed and tested, it seems likely that closed-loop control will be an integral part of future anesthesia workstations. The convenience and improved stability and response time will be important advantages in future anesthesia delivery systems.

No abstract