A comparative study of condenser humidifiers

The need for adequately humidified anaesthetic gases and the possible dangers of artificial humidification were discussed in a recent review by Boys 8i Howells.'These authors suggested that unless short-term therapeutic respiratory overhydration is required, the condenser humidifying system is the best choice for all patients with endotracheal tubes or tracheostomies.The advantages of a condenser humidifier for routine humidification have been described.They preserve the normal thermodynamic and hydrodynamic changes in the respiratory tract during respiration2 and have been considered to produce sufficient humidification of the inspired air to prevent damage to the tracheobronchial mucosa and to permit normal ciliary activity.jThe apparatus is small, light and convenient to use4 and has many less potential hazards than other methods of humidification.'Water contamination of the expiratory circuit is greatly reduced when a condenser humidifier is used.'A theory describing the performance of condenser humidifiers was propounded by Mapleson et al.'These devices can never add water to the respiratory tract and the waste gas from the condenser cannot be cooled to a temperature less than that of the fresh gas.As the waste gas is saturated with water vapour an obligatory loss from the system must take place and will equal the saturated water vapour concentration at the fresh gas temperature.has emphasised the role of the artificial airways in moisture conservation.Using a non-rebreathing circuit we measured the end-expired temperature at the upper end of the endotracheal tube.In six patients a range of values between 31 and 32.5"C was obtained.At the same site in the tracheostomy tube of spontaneously breathing patients the end-expired temperature was between 32 and 34.5"C. Types of condenser humidifiersThree types of currently available condenser humidifiers were compared to assess