Characteristics of the relative humidity and temperature in the inspiratory part of the Dräger circle system and their influence on the function of the ciliary epithelium

Changes in relative humidity and temperature of the anaesthetic gases were measured in the inspiratory limb of the Drager circle system next to the carbon dioxide absorber in 29 patients requiring ENT surgery under general anaesthesia. Immediately following intubation and prior to extubation, nasal and tracheal cytologic samples were taken with a brush technique and ciliary beat frequency was determined. At a fresh gas flow of 6 l/min, relative humidity increased from 57.6 +/- 1.5 to 62.5 +/- 1.8% (p less than 0.05) after 110 minutes. Temperature increased continuously from 21.96 +/- 0.97 degrees C to 23.83 +/- 0.48 degrees C after 200 minutes. The number of vital ciliated cells in the tracheal samples decreased from 24.4% following induction of anaesthesia to 6% at the end of anaesthesia (p less than 0.05), and from 35.7% to 26.8% (p less than 0.05) in the nasal samples. Ciliary beat frequency remained unchanged at the end of anaesthesia as compared to control in tracheal as well as in nasal samples. It is concluded that the output of relative humidity and temperature in the circle system is not sufficient to prevent broncho-epithelial damage. Ciliary beat automaticity appears to behave according to an all or nothing principle.