Membrane oxygenator

A membrane oxygenator is a device used to add oxygen to, and remove carbon dioxide from the blood. It can be used in two principal modes: to imitate the function of the lungs in cardiopulmonary bypass (CPB), and to oxygenate blood in longer term life support, termed extracorporeal membrane oxygenation, ECMO. A membrane oxygenator consists of a thin gas permeable membrane separating the blood and gas flows in the CPB circuit; oxygen diffuses from the gas side into the blood, and carbon dioxide diffuses from the blood into the gas for disposal.

The history of the oxygenator, or artificial lung, dates back to 1885, with the first demonstration of a disc oxygenator, on which blood was exposed to the atmosphere on rotating discs by Von Frey and Gruber. These pioneers noted the dangers of blood streaming, foaming and clotting. In the 1920s and 30s, research into developing extracorporeal oxygenation continued. Working independently, Brukhonenko in the USSR and John Heysham Gibbon in the USA demonstrated the feasibility of extracorporeal oxygenation. Brukhonenko used excised dog lungs while Gibbon used a direct contact drum type oxygenator, perfusing cats for up to 25 minutes in the 1930s.

Gibbon’s pioneering work was rewarded in May 1953 with the first successful cardiopulmonary bypass operation. The oxygenator was of the stationary film type, in which oxygen was exposed to a film of blood as it flowed over a series of stainless steel plates.

The disadvantages of direct contact between the blood and air were well recognized, and the less traumatic membrane oxygenator was developed to overcome these. The first membrane artificial lung was demonstrated in 1955 by the group led by Willem Kolff and in 1956 the first disposable membrane oxygenator removed the need for time consuming cleaning before re-use. No patent was filed as Kolff believed that doctors should make technology available to all, without mind to profit.

The early artificial lungs used relatively impermeable polyethylene or Teflon homogeneous membranes, and it was not until more highly permeable silicone rubber membranes were introduced in the 1960s (and as hollow fibres in 1971) that the membrane oxygenator became commercially successful. The introduction of microporous hollow fibres with very low resistance to mass transfer revolutionized the design of membrane modules, as the limiting factor to oxygenator performance became the blood resistance. Current designs of oxygenator typically use an extraluminal flow regime, where the blood flows outside the gas filled hollow fibers, for short term life support, while only the homogeneous membranes are approved for long term use.

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