OXYGENATOR

Typical Number in Hospital:

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References: 4

During heart surgery the function of the heart and lungs must be undertaken outside the body, in a heart-lung machine. Lung function is emulated in an oxygenator which must supply fresh oxygen to the blood and remove carbon dioxide. There are two main types of oxygenator: those involving direct contact between the gas and the blood and those in which the gases are required to diffuse through membranes.

The features which are sought in an oxygenator are efficient transfer, minimum blood trauma, safety and reliability, low cost and small blood priming volume.

Direct contact oxygenators are usually bubble oxygenators in which the blood passes up a column, and bubbles of oxygen rise through it. As the oxygen is taken up by the blood, carbon dioxide is released and this is vented at the top. There are many designs of columns to ensure that there is good mixing and contact between the gas and the blood. This may be a series of tubes or some kind of baffles to promote mixing. At the top of the column the blood forms a foam which must be coalesced into a reservoir. It then passes through a filter and a bubble trap.

Membrane oxygenators use a thin semipermeable membrane to separate the blood and gas phases. There is some blood trauma due to the denaturing of plasma proteins and damaging of blood cells which limits perfusion to a few hours, but these problems may be minimized by better materials for the membrane. Such oxygenators also have application in organ preservation for transplantation.

The membranes may be flat plates or closely spaced tubes. However, current membrane materials cannot be scaled to provide transfer efficiencies equivalent to the natural lung, and extra design features must be included to cause turbulence in the blood film.