Evaluation of the Datex 'Normac' anaesthetic agent monitor

The Datex 'Normac' infrared anaesthetic agent monitor has been evaluated for accuracy of calibration, stability and speed of response. Accuracy was assessed by comparing with a gas chromatograph calibrated using volumetric standards and was found to be very good for isoflurane and enflurane but was slightly less accurate for halothane, due to a low signal: noise ratio. The stability of the instrument was found to be exceptionally good. The response time is dependent on the sampling rate and we found that, in practice, the instrument would record the end expired anaesthetic concentration on patients breathing up to 15 breaths/minute. The instrument is compact and convenient for use in operating theatres.