Respiratory gas humidification

Humidification is a method for artificial heating and humidification of the breathing gas in mechanically ventilated patients. The term respiratory gas conditioning is to be understood in addition to the heating and humidifying the cleaning of the breathing gas. These three essential functions of the respiratory gas conditioning are used to prepare the inspired breathing gas for the sensitive lungs. If the natural conditioning of inspired air from pulmonary infections and damage to the lung tissue can be the result.

If a patient is ventilated for a longer time, measures to compensate for the heat and moisture loss must necessarily be taken to avoid such complications. Basically, this two methods are available: active or passive humidification. Experiments using both methods have not yet reached significance in practice.

Active humidifier

An active humidifier ensures that mechanically ventilated patients are treated with optimally conditioned breathing gas. Wherein the active humidifying the respiratory gas is supplied using, for example, electric energy to moisture and heat. According to the standard ISO 8185, the performance and safety requirements for active humidifier are set. Thereafter, the minimum water content of the inspired breathing gas will be 33 mg / l and the maximum breathing gas temperature at 42 ° C.

Depending on the physical state of water (aerosols or water vapor), the active humidifier divided into nebulizer, vaporizer and bubbler.

Nebulizer

Nebulizers create aerosols in different size droplets, which are added to the inspired breathing gas. A distinction jet nebulizer and ultrasonic nebulizer. Since nebulizer carry the risk of overhydration of the patient, they are now used only for administration of medication aerosols.

Humidifier

Evaporator enrich the inspired breathing gas with water vapor. When flow through the evaporator of the inspiratory flow is passed through a heated water bath, however, is guided along the surface of the evaporator inspiratory flow on the water surface. Consequently, the surface of the evaporator only water vapor and water droplets transported to the patient. This has the advantage that water vapor does not carry bacteria. The risk of germ transmission is therefore at the surface evaporator minimal.

A new form of the evaporator is the counter-flow evaporator, which operates on the principle of natural nasopharyngeal space. Because the air is passed through a large moist surface which is body temperature, the air is always optimally heated and humidified. Normal surface evaporator, however, have to work with an overheating of the water, making the humidification especially with the fluctuating gas flows of today's forms of ventilation can not be optimal. There is also the overheating during brief interruptions ventilation the risk of so-called hot -shot, that is a short-term very hot and humid air flow, which represents a risk for the patient.

Bubbler

When bubbler inspiratory flow is passed through a capillary system. In the capillaries circulates heated water. Anfeuchtungskapazität of the bubbler is low, but can be improved by increasing the water temperature. The use of a bubbler is usually carried out at high flow oxygen therapy via a mask or nasal tube to prevent drying of the mucous membranes or blockages in the nose and mouth.

Passive humidifier

Passive humidifier are independent of external power sources or an external water supply. You work as a heat and moisture exchanger, and heat and moisture exchanger (HME ) called, and how an artificial nose between the tube and the Y-piece placed. There they escape the exspiriertem breathing gas heat and moisture and run it in the subsequent inspiration the respiratory gas again. Due to significant qualitative differences exclusively HMEs should be used to ensure an effective humidification. This HMEs are preferable with high reversible water retention capacity, low internal volume and low flow resistance.

To take enough water and heat, the HME must be completely traversed by the expiratory gas flow. When leakage occurs, such as in patients with bronchial fistulas that condition is not met. A risk also exists in patients with increased production of secretions, bleeding, etc. This can lead to the relocation of the HMEs. In these cases, the use of active humidifier is recommended.