BLOOD PRODUCTS
B
MEASURING BLOOD PRESSURE
Blood pressure measurement is a
routine part of a physical examination.
A sphygmomanometer measures blood
pressure as systolic (the top figure),
when the heart contracts, and
diastolic, when the heart relaxes.
An inflatable cuff attached to the
sphygmomanometer is wrapped
around the upper arm and deflated
while a doctor listens to the blood flow
through an artery, using a stethoscope.
S p h y g m o m a n o m e t e r
created by the contraction of the ventri-
cles of the
heart.
Diastolic, the lower
pressure, is recorded during relaxation
of the ventricles between heartbeats; it
reflects the resistance of all the small
arteries in the body and the load against
which the heart must work. The pres-
sure wave that is transmitted along the
arteries with each heartbeat is easily felt
as the
pulse.
Blood pressure is measured using a
sphygmomanometer
and is expressed as
millimetres of mercury (mmHg). Blood
pressure varies with age, between indi-
viduals, and at different times in the
same individual. A healthy young adult
usually has a blood pressure reading, at
rest, of about 120/80 (120 mmHg sys-
tolic and 80 mmHg diastolic pressure).
A sustained level of high blood pressure
is called
hypertension;
abnormally low
pressure is termed
hypotension.
blood products
Donated blood (see
blood donation)
that
is separated into its components: red
cells, white cells, platelets, and plasma.
Each blood product has a specific life-
span and use in
blood transfusion.
Packed
red cells (blood that has most of the
plasma removed) are used to treat indi-
viduals with some forms of chronic
anaemia
and babies with
haemolytic dis-
ease of the newborn.
Washed red cells
(with white blood cells and/or plasma
proteins removed) are used when a per-
son requires repeated transfusions since
there is less risk of an
allergy
to any of
the blood components developing.
Platelets may be given through trans-
fusions for those people who have
blood-clotting disorders. Patients who
have life-threatening infections may be
treated with granulocytes, a type of
white blood cell. Fresh frozen plasma is
used to correct many types of
bleeding
disorder
because plasma contains all
the clotting factors. Plasma substitutes
may be used to treat
shock
that has
occurred as a result of severe blood loss,
until sufficient compatible whole blood
becomes
available.
Purified
albumin
preparations are used for people who
have
nephrotic syndrome
and
chronic
liver disease.
Concentrates of blood clotting factors
VIII and IX are used in the treatment
of the conditions
haemophilia
and
Christ-
mas disease. Immunoglobulins
(also called
antibodies), which are extracted from
blood plasma, can be given by injection
(see
immunoglobulin injection)
to protect
those people who are unable to produce
their own antibodies or have already
been exposed to an infectious agent.
Immunoglobulins may also be given to
provide short-term protection against
hepatitis A.
Immunoglobulins are given
in large doses to treat certain
autoim-
mune disorders
.
blood smear
See
blood film.
blood sugar
See
blood glucose.
blood test, haematological
Analysis of a sample of blood to provide
information about its cells and proteins
and the chemicals, gases, antigens, and
antibodies it contains. Haematological
blood tests are used to check respiratory
function,
the
immune
system,
the
metabolism,
hormonal
balance,
and
the health of the major organs. The tests
look at the numbers, appearance, shape,
and size,
of blood cells and assess
the
function
of clotting
factors
in
the blood.
TYPES
Important haematological blood tests
are
blood count
and
blood group
tests if a
blood transfusion is needed. Biochemi-
cal tests measure chemicals in the blood
(see
acid-base balance; kidney function
tests;
and
liver function tests).
Microbiol-
ogical tests (see
immunoassay)
look for
microorganisms that are in the blood,
such as in septicaemia. Immunological
tests also look for antibodies in the
blood, which may confirm immunity
to an infection.
blood transfusion
The infusion of large volumes of blood
or of
blood products
directly into the
bloodstream to remedy severe blood
loss or to correct chronic
anaemia.
In an
exchange blood transfusion, nearly all
of the recipient’s blood is replaced by
donor blood.
HOW IT IS DONE
Before a transfusion, a sample of the
recipient’s blood is taken to identify
his or her
blood group,
which is then
matched with suitable donor blood. The
donor blood is transfused into an arm
vein through a plastic cannula (a tube
with a smooth tip). Usually, each unit
(about 500 ml) of blood is given over
one to four hours; in an emergency,
5 00 ml may be given within a couple of
minutes. The blood pressure, body tem-
perature, and pulse of the patient are
monitored during the procedure.
COMPLICATIONS
If mismatched blood is accidentally
introduced into the circulation, anti-
bodies in the recipient’s blood may
cause the donor cells to burst, leading
to
shock
or
kidney failure.
Less severe
reactions can produce fever, chills, or a
rash. Reactions can also occur as the
result of an allergy to a particular com-
ponent of the transfused blood.
The risk of infection is extremely
small. All blood used for transfusion is
carefully screened for a number of infec-
tious agents, including
HIV
(the
AIDS
virus) and
hepatitis B
and
hepatitis C.
In elderly or in severely anaemic
patients, blood transfusion can overload
the circulation, leading to heart failure.
In patients with chronic anaemia who
need regular transfusions over the course
of many years, excess iron may accumu-
late (a condition called haemosiderosis)
and damage organs such as the heart,
liver, and pancreas. Treatment with the
drug
desferrioxamine
to remove excess
iron may be needed in this case.
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