An evaluation of three volatile anaesthetic agent monitors.

Three volatile anaesthetic agent monitors (Datex Normac Anesthetic Agent Monitor, Engstrom Emma Multigas Monitor and Penlon Halothane Meter) were evaluated for the effects of nitrous oxide or water vapour, and for their linearity, stability, and rate of response to a change in concentration of various anaesthetic agents under simulated working conditions. None was affected by nitrous oxide, and only the Engstrom Emma was affected by water vapour. Linearity was satisfactory for all three devices but stability, with respect to zero and gain drift, was satisfactory only for the Datex Normac and Penlon Meter. Rates of response for 10% to 90% of source signal ranged from 0.8 seconds for the Datex Normac to about three seconds for the Penlon Meter.