Ultrasound detection of emboli in brain during surgery reduces stroke
20 February 2008
Surgeons at the University of Leicester have developed a new technique to
detect emboli (harmful blood clots/air bubbles in arteries) that has helped
reduce stroke rates after carotid endarterectomy. This is an operation
designed to remove narrowings in the main arteries supplying the brain
before they can cause a stroke.
The emboli detection techniques were developed by Professor David H Evans
and Professor A Ross Naylor in the Department of Cardiovascular Sciences at
the University of Leicester and involve the use of Doppler ultrasound, the
same technique used to detect the foetal heartbeat in pregnant women. The
work was recently presented at an international conference on Ultrasound in
Medicine in Australia.
Before per-operative embolus monitoring was introduced in 1992, the
intra-operative stroke rate during carotid artery procedures was 4%. Today
it is 0.2%. Before post-operative monitoring was introduced in 1995, the
post-operative stroke rate was 2.7%. Today it is extremely rare. Overall,
the 30-day death/stroke rate has fallen from 6% to 2.6%.
In the new technique, an ultrasound transducer is placed on the side of
the patient’s head, just in front of the ear, and is used to detect the
movement of emboli through blood vessels in the brain. The technique is
painless and harmless.
If emboli are detected appropriate measures can be taken to reduce or
prevent the embolism from occurring. In some patients the monitoring will
continue for 1 or 2 hours post-surgery. This reduces the likelihood of the
patient suffering a stroke.
Emboli may be pieces of atheroma that have been dislodged from diseased
arteries, they may be blood clots, or they may be air bubbles accidentally
introduced into the blood.
They travel through the circulation until they become ‘wedged’ in an
artery. This prevents blood flow in that artery and therefore starves the
tissue supplied by that artery of its blood supply and thus oxygen.
This can lead to the death of the affected tissue. If this occurs in the
brain it leads to stroke, if it occurs in the heart it leads to myocardial
In general, small solid emboli are much more likely to cause stroke than
similarly sized gaseous emboli, and one of the techniques the Leicester
scientists have developed helps them to distinguish one from the other.
Professor of Medical Physics at Leicester, David Evans, commented: “We
have been involved in cerebral embolus research here in Leicester for over
15 years. Much of our work to date has centred on improving the safety of
carotid artery surgery.
“More recently we have started to work with cardiac surgeons on embolism
during open-heart surgery, in the hope of reducing potentially harmful
effects on the brain of open-heart surgery.”
Consultant vascular surgeon Professor Naylor said, “The paradox with
carotid endarterectomy is that although this is a proven operation for
preventing stroke in the long term, it is also directly responsible for
causing a stroke in a small number of patients in the peri-operative period.
The lower the initial risk, the greater the long-term benefit.
“The research performed here in Leicester has contributed towards a 60%
sustained reduction in the overall operative risk which translates into
greatly enhanced long-term benefit to the patient and considerable
rehabilitation savings to the NHS.”
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