Biomedical Engineering Reference
In-Depth Information
capacity due to better thermal conductivity of metal over polymer materials. The
latter are easier to process and provide better biocompatibility.
A recent development is to include an arterial filter into the oxygenator, as
thrombus formation or introduction of other particulates or gaseous emboli is of
concern.
The final device will need to be sterilised before use. As the most widespread
membrane material, PP, is not gamma stable, oxygenators are sterilised with
ethylene oxide (ETO) gas. An oxygenation membrane from PE (`OXYRAY',
Membrana GmbH, Germany), which can be sterilised by gamma irradiation,
gained little market share in the 1980s and is no longer commercially available.
1.2.9 Alternative technologies
Cardiac surgery can also be performed without the aid of extracorporeal cir-
culation and thus without an oxygenator. This means that during the procedure
the heart needs to keep beating and supplying blood to the body and brain. This
of course is only possible for surgery on the outside of the heart such as coronary
artery bypass surgery. The site of the intervention is stabilised with a suction
device, so that the surgeon can perform the bypass operation on the otherwise
beating heart. Recent studies indicate that results of this form of surgery are
somewhat inferior to the classical stopped heart surgery.
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In the late 1990s this
kind of procedures were reinvented and reintroduced to the surgical community
and rapidly gained acceptance. But since operating on a beating heart is more
stressful and demanding to the whole surgical team, the off-pump procedures
ceased their growth some years later and since about 2002/2003 account for
about 20% of all bypass procedures.
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Other options for interventions on the coronary arteries include balloon
angioplasty and stenting, where a tiny balloon is forwarded to the narrowing of
the artery and then inflated to reopen the clogged section. This can also be
combined with a stent, a tiny metal wire mesh around the balloon, which is left
in place in the artery to prevent a re-narrowing. Most recent products are coated
with growth inhibitors, so that the lumen of the artery stays open for prolonged
time. This intervention is of course less invasive, as it is done through a simple
cannulation of the arteries, whereas the surgical intervention includes opening
the chest. The downside is that through the tortuous arteries not every part of the
coronary system can be reached and reopened equally well with a balloon or
stent. Additionally, the reintervention rate is higher for the latter approaches, as
despite most recent developments the re-narrowing (restenosis) of the arteries
still is significantly higher with angioplasty and stenting than with coronary
artery surgery.
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There currently is no real alternative for long-term lung support. Mechanical
ventilation may assist or even replace spontaneous breathing for some time. This
can be done with negative pressure (sucking air into the lungs) or positive
