Oxygenator
An oxygenator is a medical product, the blood with oxygen enriched and carbon dioxide from the blood removed. It is used to maintain gas exchange in cardiac surgery as an individual part of the heart-lung machine and in intensive medicine for the treatment of acute lung failure . The oxygenator temporarily replaces the function of the lungs . There are film, bubble and membrane oxygenators, the latter being used almost exclusively in Germany.
Film oxygenator
The first oxygenator was the Mayo Gibbon Sieve Oxygenator from 1953 (named after the Mayo Clinic and surgeon John Heysham Gibbon ). The blood conveyed by a roller pump flows over large sieves in an almost pure oxygen environment. The gas exchange takes place on the enlarged blood surface.
Disk oxygenators followed the same principle: disks rotate in a horizontal cylinder, about a third of which are immersed in blood and are thus covered by a blood film, on whose enlarged surface the gas exchange takes place.
Both processes can hardly be controlled. The materials have to be laboriously cleaned and sterilized after each use . In addition, direct extensive contact with oxygen is not very gentle on the blood. Plasma proteins are denatured , platelets and erythrocytes are attacked and can be damaged.
Bubble oxygenator
With the bladder oxygenator, gas is dispersed in blood. As early as 1955, blood could be enriched with oxygen through gas bubbles. To do this, gas bubbles are allowed to rise up in a column of blood. The gas exchange takes place directly on the surface of the gas bubbles.
When the gas flow is increased, more and smaller bubbles are created, which increases the saturation power.
As with the film oxygenator, however, the partial pressure of the oxygen cannot be controlled independently of the partial pressure of the carbon dioxide . Under certain circumstances, carbon dioxide even has to be added again to the gas mixture. A defoamer must be used to minimize the risk of micro- embolism caused by gas bubbles .
Despite its disadvantages, this type of oxygenator has been responsible for major advances and widespread use in cardiac surgery.
Membrane oxygenator
The membrane oxygenator with a semipermeable membrane between blood and gas was used for the first time in 1956, and on a larger scale since around 1980. Today, practically only this type of oxygenator is used in Germany.
In this process, the gas and blood sides are separated by a membrane - similar to the human lungs. The gas exchange takes place along the gas-permeable membrane due to the partial pressure differences of the gases involved. The mixture of compressed air and oxygen is adjusted by means of a gas blender (electronic or analog).
In terms of fluid dynamics, it is difficult to find a compromise between blood damage, thrombosis tendency and good gas exchange. For this reason, coatings are used in all membrane oxygenators today. These coatings mostly consist of heparin, but there are also heparin-free polymer coatings. These polymers are mostly amphiphiles. These polymers make the previously hydrophobic fiber surface hydrophilic. As soon as a liquid is passed along the membrane fiber, a thin film of water molecules forms on its surface, which results in lower friction and lower thrombogenicity.
There are two types of oxygenation fibers:
- Polypropylene- based fibers (highly porous, not plasma-tight)
- Polymethylpentene- based fibers (plasma-tight).
In the case of polypropylene-based fibers (PP), blood plasma can pass from the blood phase of the oxygenator into the gas phase; the so-called plasma leakage. A foam is formed which reduces the gas flow through the oxygenator and thereby reduces the gas transfer performance of the oxygenator. Polypropylene membranes have microporous capillaries that have excellent gas exchange properties, but are also permeable to small amounts of blood plasma in the long term. You will find their use z. B. in the heart-lung machine and are approved for periods of use in the hour range. Furthermore, PP fibers are permeable to anesthetic gases such as B. sevoflurane or desflurane . It is thus potentially possible to continue a gas anesthesia during a cardiac surgery operation through the extracorporeal circulation. The usefulness of this function is controversial; the available studies on this are inadequate.
Plasma-tight fibers consist of polymethylpentene (PMP) and have a plasma-tight coating, which means that they are approved for periods of use of up to 14 days. They are used for extended extracorporeal circulation (ECMO) . They do not develop any plasma leakage, but have a slightly lower gas transfer performance than polypropylene-based membrane oxygenators. Due to the smoother surface, the PMP membranes are more gentle on the blood and indicate improved biocompatibility.
Membrane oxygenators are sterile single-use products and therefore do not need to be cleaned or reprocessed.
Heat and cold transfer
All oxygenators used today also have a heat exchanger that can heat or cool the blood flowing through with the help of water. Both systems made of stainless steel and capillary systems made of plastic are used for this. In order to increase efficiency, the blood always flows against or across the direction of flow of the water.
Integration of further functions
The development goes towards the integration of further functions in the oxygenators, e.g. B. Pump function through integrated centrifugal pump , balloon pump or integrated sensors for relevant blood parameters. This integration reduces the extracorporeally conveyed volume, which means that side effects of oxygenator therapy such as anemia , hypothermia , hemolysis , coagulation or platelet aggregation are reduced.
literature
- Reinhard Larsen: Anesthesia and intensive medicine in cardiac, thoracic and vascular surgery. (1st edition 1986) 5th edition. Springer, Berlin / Heidelberg / New York et al. 1999, ISBN 3-540-65024-5 , pp. 81-88.
Individual evidence
- ^ Karl Vossschulte , Hanns Gotthard Lasch and F. Heinrich (editors): "Internal medicine and surgery", 2nd edition, Thieme-Verlag , Stuttgart and New York 1981, ISBN 3-13-562602-4 , page 62.
- ↑ a b A. Philipp, M. Foltan, F. Schettler, M. Gietl, A. Thrum, S. Schmidt, A. Holzamer, T. Müller, T. Bein, K. Lehle, C. Schmid: Long-term function of oxygenators with extracorporeal lung support. In: cardio technology. 1/2009 ( Memento of the original from April 6, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , ISSN 0941-2670 , pp. 3-7 ( PDF file ).
- ↑ a b Cardiohelp - The world's smallest heart-lung machine saves lives from October 29, 2008 European Hospital Online ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .
- ↑ A. Strauss, H. Reul, U. Steinseifer, T. Schmitz-Rode: Development of a mobile membrane oxygenation system (HEXMO) for the gentle therapy of acute, severe lung failure ( ARDS ) . In: cardio technology. 3/2006 ( Memento of the original from April 2, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , ISSN 0941-2670 , pp. 80-81 ( PDF file ).
- ^ R. Borchardt, P. Schlanstein, I. Mager, J. Arens, T. Schmitz-Rode, U. Steinseifer: In Vitro Performance Testing of a Pediatric Oxygenator With an Integrated Pulsatile Pump. In: ASAIO. July / August 2012 58 (4), DOI: 10.1097 / MAT.0b013e318251dc70 , ( pp. 420-425 ).
- ↑ Kopp, Ruedger; Bensberg, Ralf; Arens, Jutta; Steinseifer, Ulrich; Schmitz-Rode, Thomas; Rossaint, Rolf; Henzler, Dietrich A Miniaturized Extracorporeal Membrane Oxygenator with Integrated Rotary Blood Pump: Preclinical In Vivo Testing In: ASAIO Journal May / June 2011, (57) 3 DOI: 10.1097 / MAT.0b013e31820bffa9 , pp. 158-163 ( [1] ).
