Oxygenator

An oxygenator is a medical product, the blood enriched with oxygen and removes carbon dioxide from the blood. It is used in cardiac surgery as part of the heart -lung machine and in intensive care for treatment of acute lung injury. The oxygenator is replaced for a short time, the function of the lungs. There are film, bubble and membrane oxygenators, whereby the latter is used almost exclusively in Germany.

Filmoxygenator

The first oxygenator was the Mayo - Gibbon Sieboxygenator of 1953 (named after the Mayo Clinic and the surgeon John Heysham Gibbon ). Funded by a roller pump blood flow through large screens in almost pure oxygen environment. To the so- increased blood surface of the gas exchange takes place.

The same principle pursued Scheibenoxygenatoren: In a horizontal cylinder rotating discs, which dip to about one third in the blood and are thus covered by a blood film, takes place at the enlarged surface area of gas exchange.

Both methods are hard to control. The materials must be cleaned and sterilized meticulously after each use. In addition, the large-scale direct contact with oxygen is little blood gently. Plasma proteins are denatured, platelets and red blood cells are attacked and can be damaged.

Bubble oxygenator

In 1955 blood could be enriched by gas bubbles with oxygen. Do this, we ascend gas bubbles in a column of blood. Gas exchange takes place directly on the surface of the gas bubbles.

When the gas flow is increased, it produces more and smaller bubbles, thereby, the saturation power increases.

As with Filmoxygenator the partial pressure of oxygen can but do not independently control the partial pressure of carbon dioxide. Under certain circumstances, the gas mixture of carbon dioxide must be added even again. To minimize the risk of micro- emboli by gas bubbles, a defoamer must be employed.

Despite the drawbacks of this Oxygenatortyp was responsible for significant progress and a large spread of cardiac surgery.

Membrane oxygenator

The membrane oxygenator was used for the first time in 1956, on a larger scale since about 1980. Today in Germany, only this Oxygenatortyp is practically used.

In this method, the gas separated from the blood side by a membrane - similar to human lungs. Gas exchange takes place along the gas-permeable membrane by partial pressure of the gases involved. The mixture of compressed air and oxygen gas is adjusted by means of a blender (electronic or analog).

It is aerodynamically difficult to find a compromise between blood damage, thrombosis and good gas exchange. For this reason nowadays coatings come in all membrane oxygenators used. These coatings usually consist of heparin, but there are also heparin-free polymer coatings. These polymers are often amphiphiles. These polymers by the previously hydrophobic fiber surface hydrophilic. When liquid is supplied to the membrane along the fiber, forms on its surface a thin film of water molecules, thereby forming a lower friction and a lower thrombogenicity is achieved.

There are two types of oxygenator fibers:

For polypropylene -based fibers ( PP) may occur for the transfer of blood plasma from the blood phase of the oxygenator in the gas phase; the so-called plasma leakage. It forms a foam, which reduces the gas flow through the oxygenator, and thereby decreases the gas transfer capacity of the oxygenator. Polypropylene membranes have microporous capillaries, which have excellent gas exchange characteristics, but in the long term also permeable to small amounts of blood plasma. They are used for example in the heart -lung machine and are approved for use periods of several hours. Furthermore, PP fibers are permeable to anesthetic gases such as sevoflurane or desflurane. Thus, it is potentially possible to continue a gas anesthesia during cardiac surgery by the extracorporeal circulation. The benefit of this function is controversial; the study location for this is insufficient.

Plasma density fibers are made of polymethyl pentene (PMP ) and have a plasma dense coating, which they are approved for use periods of up to 14 days. They are used for prolonged extracorporeal circulation ( ECMO). You do not develop plasma leakage, but have a somewhat lower gas transfer performance than polypropylene -based membrane oxygenators. The smoother surface of the PMP membranes are blood compatible and indicate improved biocompatibility.

Membrane oxygenators are sterile disposables and do not need to be cleaned or treated.

Heat and cold transfer

All oxygenators used today in addition possess a heat exchanger which can heat or cool the blood with the help of water. For both systems made ​​of stainless steel and plastic capillary systems are used. To increase the efficiency, the blood is always flowing against or across the direction of water flow.

Integration of additional functions

The development is the integration of additional functions in the oxygenators, such as pumping function through integrated centrifugal pump, balloon pump or integrated sensors for relevant blood parameters. This integration reduces the volume exktrakorporal funded, which concomitants of oxygenator therapy such as anemia, hypothermia, hemolysis, coagulation or platelet aggregation can be reduced.