[Equipment for respiratory gas conditioning under hygienic conditions]

The significance of respiratory gas conditioning systems as sources of germ colonization and infection of the respiratory tract results from the principle of operation and the temperature. Six respiratory air humidifiers were tested for their hygienic risk in experiments with test germs. Contrary to several reports, some humidifiers were shown to accumulate microorganisms, whereas others do not promote germ population in the respiratory tract even though the water of the humidifier is heavily contaminated. It could be confirmed that basic differences exist between "blow over" and "blow through" humidifiers in the accumulation of microorganisms in respiratory air. Moreover, our investigations revealed that even "blow over" humidifiers should not be considered completely harmless. The "blow over" apparatuses Hydrotrop 200, Aquapor and VH 620 (infant) did not cause any germ propagation in the resuscitation tubes, whereas in the "blow through" apparatuses Bennett Cascade and VH 620 (adult) germ propagation is quite considerable. The mortality kinetics of the germs differ depending on the temperature and the type of apparatus used and should be taken into account when it comes to choosing or developing respiratory gas conditioning devices. Constant heating of the water in the humidifier to a minimum of 50 degrees C provokes a bactericide behaviour of the problem germs. Therefore, it is quite justifiable to do without expensive internationally recommended measures if the humidifier is well chosen. The requirement to replace the humidifier every 24 hours in long-term artificial respiration need not be observed for devices classified as harmless if aseptic handling is guaranteed, i.e. if manual germ transmission by the staff is avoided.