SummaryIn a double-blind trial, 50patients were randomly allocated to receive up to 0.29

SummaryThe performance of the E M 0 inhaler has been studied. The concentrations of ether delivered were most accurate when higher concenrrations were selected and when higher tidal volumes occurred. Key words Equipment; vaporizers.The E M 0 inhaler was described by Epstein and Macintosh in 1956' as an improved version of the Oxford Vaporizer.Since then there have been reports on the use of the inhaler in clinical s i t~a t i o n s . ~~~ In addition its advantages have been emphasised and a plea for the use of draw-over vaporizers, including the EMO, has recently been made. 4 Despite the fact that it has been in use for a number of years, principally in research centres and with the armed forces, we can only find one published report on its performance.' However this report gives minimal data on only some of the control settings.A study was therefore set up to establish the ether concentrations delivered at each control setting when the tidal volume and frequencies were altered. Material and methodsA standard E M 0 inhaler was used. Air was drawn through the inhaler using a Starling Ideal pump, which delivers an intermittent flow. Ether concentrations were measured using a Medishield MS2 mass spectrometer of the quadrupole type. Different scale settings, tidal volumes and frequencies were selected and after a period of 5 minutes following each change the reading was taken from the mass spectrometer. The mass spectrometer was calibrated to a mass number of 59.5, and the probe was sited as close as possible to the outlet of the inhaler so as to minimise any solution of the ether in the hose connexions (Fig. I). The study was conducted at a room temperature of 21 "C.