Breathing gas humidification is a method of hyperthermic heating and humidification of breathing gas in mechanically ventilated patients. The term “breathing gas conditioning” means, in addition to heating and humidifying, the purification of the respiratory gas. These three essential functions of respiratory gas conditioning are used to prepare the inspired respiratory gas for the sensitive lungs. If the natural breathing gas humidification persists, pulmonary infections and damage to the pulmonary tissue can occur.