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Stroke
Prevention using Transcranial Doppler and Blood Transfusion
How do transfusions work?
Only red blood cells, which carry oxygen, are given to the patient. It is
not clear how transfusion prevents stroke, but we know that it increases the
ability of the blood to carry oxygen to the brain and other organs and
lowers the number of sickle red blood cells in the bloodstream. These
effects may stabilize or reverse the conditions in the abnormal brain
arteries and prevent the development of stroke.
How safe is transfusion?
The blood supply in the US and Canada is very safe, but risk can never be
totally eliminated. Patients in the STOP study were monitored for evidence
of blood-borne infections, and at the end of the study, there was no
indication of any infection caused by transfusion in over 1500 transfusions.
Transfusion also causes a build-up of iron in the body which can affect
vital organs. When red blood cells break down, the iron that is part of each
cell is stored in the heart, liver, and other organs. Transfused blood is
broken down more rapidly and iron overload becomes a health concern. If a
child receives long-term transfusions (3-5 years), chelation is recommended
to control the build-up of iron.
Other potential problems are associated with transfusions, including
alloimmunization and other reactions. These reactions can be reduced by
better matching of blood factors, but cannot yet be eliminated.
How long must children be treated with transfusion after a first-time
stroke?
Transfusions used to prevent a second stroke are usually continued at least
until the child grows to adulthood. Even then it is not clear how safe it is
to stop transfusions. For now, children must remain on treatment
indefinitely until further research determines when transfusion can be
safely stopped or replaced by another therapy. STOP II is attempting to
provide some answers to this question.
Will blood transfusions prevent strokes in all children at risk?
No, STOP data indicate that a small number of children may still have a
stroke despite transfusion treatment.
Are there alternatives to transfusion?
Although there is an interest in the use of hydroxyurea, and more standard
stroke prevention treatments such as antiplatelet agents and
anticoagulation, no clinical trial data support their use for this
indication.
Bone marrow transplantation (BMT) can cure SCD, and presumably has the
potential to prevent cerebrovascular disease and stroke. Experience with BMT
is insufficient to know how well this would work in stroke, although it
seems to arrest development of cerebrovascular disease in the small number
of patients with stroke and BMT. In France, abnormal TCD is used as an
indication for BMT, however opinion is divided in the United States on using
abnormal TCD as a sole indication for BMT.
Treatments which are as effective as transfusion but with fewer side effects
would represent a great advance in this field and are being considered for
investigation. At present, only chronic transfusion is both supported by
Class I evidence (a randomized clinical trial of sufficient size and
quality) and endorsed by the
National Heart,
Lung, and Blood Institute.
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