Induced hypothermia protects the brain following stroke
8 March 2012
Inducing mild hypothermia can reduce the side effects of
treatment for blood clot in the brain following a stroke.
Thromboembolic stroke, caused by a blood clot in the brain,
results in damage to the parts of the brain starved of oxygen.
Breaking up the clot with tissue plasminogen activator (tPA)
reduces the amount of damage, however, there is a very short time
window when the value of the treatment outweighs the side effects.
New research published in BioMed Central's open access
journal Experimental & Translational Stroke Medicine shows
that, during the first 24 hours after a stroke, mild hypothermia
(34C) can reduce the side effects of tPA and potentially increase
the window of opportunity for tPA treatment.
When a blood clot blocks off blood flow in the brain (ischemic
stroke) the part starved of oxygen quickly begins to die. In order
to prevent significant damage tPA must be given to the patient as
early as possible after the onset of symptoms - doctors recommend
that it must be administered within the first four and a half hours.
Delayed treatment also increases the patient's risk of intracerebral
hemorrhage and brain swelling (edema).
Mild hyperthermia is known to be neuroprotective and to reduce
damage caused by the return of blood flow to an area of the brain
starved of oxygen by a clot. Researchers from the University of
Erlangen, led by Dr Rainer Kollmar, tested whether mild hyperthermia
could also prevent damage to the brain due to tPA treatment in rats.
After 24 hours they found that, while hypothermia reduced the
amount of swelling and damaged tissue in the brain after a stroke,
tPA (administered 90 minutes after the onset of stroke) increased
it. However, they also discovered that hypothermia therapy was able
to offset the damage due to tPA.
This seemed to be true for all the measurements they looked at.
Dr Kollmar explained, "Patients often loose brain function such as
control over parts of their body, speech or memory after stroke. We
looked at 'neuroscore', to examine how much control of the body had
been affected, and at markers for inflammation (TIMP-1 and sICAM) or
evidence of damage to the blood brain barrier. In all cases
hypothermia was able to offset the side effects of tPA."
While these results are still experimental, new techniques which
prevent shivering mean that this technique is easier to administer
in conscious patients. Preliminary clinical trials are also
beginning to show that it is possible to treat patients, who have
had a stroke, with tPA plus hypothermia. Our results suggest that
hypothermia can offset the side effects of tPA and further studies
will show if it is also able to increase the window of opportunity
of tPA treatment in patients.
Bernd Kallmünzer, Stefan Schwab and Rainer Kollmar. Mild
hypothermia of 34C reduces side effects of rt-PA treatment after
thromboembolic stroke in rats. Experimental & Translational Stroke
Medicine (in press)
See also MTB Europe article:
cooling reduces heart and brain damage after MI, cardiac arrest and