Service improves performance of unattended draw-over halothane vaporizers

The accuracy of the output halothane concentration of seven draw-over halothane vaporizers (TEC, Ohmeda) which were delivered in 1986 to Malawi was investigated. They had not been serviced for the past 8 years. The output was studied at dial settings of 0.5%, 1%, 2%, 3%, 4%, and 5% at minute volumes of 2 to 8 litres before and after thorough cleaning of the vaporizers. The measured halothane concentration was corrected to sea level. Of seven vaporizers one was delivering concentrations up to 240% higher than the setting. A second vaporizer delivered concentrations much lower than the setting; the maximum output was 1.5% at the 5% setting. After cleaning, all vaporizers delivered concentrations close to the dial setting. The maximum deviation from the setting was 0.5% at the 0.5%, 1% and 2% setting and 0.9% at higher settings. Whether the replacement of damaged wicks and seals would improve the accuracy further could not be investigated because these spare parts were not available. It is concluded from this study that regular servicing of draw-over vaporizers is essential. Support for the training of technicians in developing countries and also support for the funding of spare parts and measuring instruments in these countries should be considered by donors.