Dipl.-Ing. Jutta Arens
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Patients with acute lung failure (ARDS) urgently need mechanical ventilation. Thereby, oxygen is pressed into the blood via areas of intact lung tissue, and the diseased lung tissue does not get the chance to recover and regenerate. In addition, healthy tissue might be damaged by high pressures. Therefore, the use of membrane oxygenators is often the last option for ARDS patients. Extracorporeal Membrane Oxygenation ECMO preserves lung tissue and is able to sufficiently supply the patient with oxygen and to effectively eliminate CO2. ECMO is established since many years in neonatalogy and pediatry.
In ECMO gas exchange is provided through semi-permeable membranes. Oxygen is supplied to the blood and carbon dioxide taken out. The blood is usually forwarded by a roller or centrifugal blood pump through a tubing system. For control of the blood temperature heat exchangers are integrated in the extracorporeal blood circuit. The relatively large blood contact surfaces in current systems result in high risk of complications such as infections, haemolysis, thrombus formation and bleeding, the latter caused by the necessary anticoagulation during therapy. The application of ECMO as an adult therapy is therefore contended.
The Cardiovascular Engineering group develops a highly integrated, extracorporeal membrane oxygenator HEXMO as a compact oxygenator with an already integrated rotary blood pump. Thus, the priming volume and the blood contact surface are substantially reduced. In addition, a heat exchanger may become redundant. HEXMO's compact design shall thereby reduce bleeding, infection, haemolysis and thrombosis risks and make it easy to handle.
The new HEXMO system is optimized with regard to low priming volume and blood contact surface. Its operational readiness and minimal invasive application shall be additionally fostered by use of a double lumen cannula. HEXMO shall be applied for the instantaneous treatment of ARDS patients.
The HEXMO principle is shown in Fig. 1. The integrated rotary blood pump with reusable drive unit with magnetic coupling and pumphead pumps venous blood from the vena cava through a double lumen cannula and the blood inlet along the inner and outer hollow fiber membranes of the oxygenator. Oxygen flows through the oxygen inlet parallel through the inner and the outer hollow fibers. The blood flow reverses its flow direction between the inner and out membrane bundles. After the gas exchange the unused O2 and the removed CO2 stream out of the oxygenator through the gas outlet. The oxygenized blood is pumped through the blood outlet, which is located on the same side of the oxygenator as the blood inlet, and the double lumen cannula back into the systemic blood circuit.
Fig. 2 shows the attachment of the HEXMO to the patient. The concentric double lumen cannula is connected to an adapter of the oxygenator and is placed in the vena cava via the vena femoralis.