Okay, we need to get all that crossmatching right
but there are still complications
of blood transfusions that you must be very aware of.
The first one I will focus on is hemolysis
that means breakdown of red cells and there are two major
types, which I have already touched on during this lecture.
The first is the immediate IgM-mediated lysis
or destruction of the red cells.
Let me go through that in a little bit more detail.
This means if you infuse a red cell into a patient and they
already have antibodies against typically A, B, O
against those red cells, these IgM antibodies will
stick to the red cells within minutes.
They will destroy them and release that
free haemoglobin into the patient's blood.
That can be very serious, indeed fatal and was a major cause
of fatalities from blood transfusions in the very early days.
The second type of hemolytic reaction is where
the antibody is delayed.
There is no antibody present within the
patient against the infused red cells
but there is a protein mismatch and the antibody
gets developed over a next week or two
I have already shown you that that leads to perhaps less
significant clinical problems, delayed jaundice
or delayed anaemia, then it causes the infections that
we have mentioned. Occasionally, bacterial infections
can be transferred from a blood donation, and they can be
quite serious and very rapidly overwhelming in the patient.
Fortunately, they are rare. Viral infections such as HIV
and hepatitis C can be transmitted.
Fortunately transmission of HIV was exceptionally rare
and remains so to this day.
There are other infections as well that may be transmitted,
but it is now a very rare problem.
Finally, iron accumulation can occur in patients
who have regular blood transfusions.
I will address that in more detail in a minute.
Now let us look at how we might use these products.
On the right, you will see a classic red cell unit.
It is concentrated and ready to give to a patient
who has anaemia.
Now I've said in that left-hand column that, typically
you might give that for patient
who has haemoglobin less than 80g per liter;
but that cut- off needs to be interpreted with caution
and in particular for the state of the patient.
If somebody is breathless because of anemia,
then you might want to increase it, you can give blood
at haemoglobins of 100 or 120. It's really just a guideline.
However, I would make the point that in general the
threshold for transfusion has decreased in recent years.
So even after an operation or somebody in an
intensive care unit doctors are not so quite prone
to give blood transfusions as they used to in the past.
The reason for that well as you've seen from this lecture,
a blood transfusion is quite complicated and costly to produce.
But also it seems that patients can do quite well with
slightly lower hemoglobin particularly
when they are critically ill, and that is definitely
a trend within blood transfusion across the world.
Now for people who are not making any red cells, those
whose bone marrow's completely dysfunctional,
they'll need transfusions about every three weeks
because red cells as we know live around 120 days
so we need to keep topping them up.
Now interestingly with any units of blood,
there is 200 mg of iron.
Now that's perhaps an unusual fact to each of you at this
stage but you have 5 grams of iron within your body,
only 5 grams and with 200 grams in each bag of blood,
you can see that if you are having regular
blood transfusions, you will rapidly increase
the iron in your body.
Now iron can be toxic to a range of tissues.
So if the people who need very regular blood transfusions
perhaps for life, we have to extract that iron
called iron chelation and now there are tablets that
can do that.
Of course as I've said many times, the major
concern with blood cell transfusions
is that we get the ABO system matched correctly.
Let us talk about fresh frozen plasma.
I said right at the start that this is generated
by taking the plasma off a blood donation and
freezing it until it is needed.
Now fresh frozen plasma/FFP as it's known, contains clotting
factors and is widely used in patients
who have blood-clotting disorders, a wide range of
conditions can lead to that.
It has no value as a blood volume expander.
If the patient has bled a lot and so forth,
there's absolutely no point giving fresh frozen plasma.
It's really useful for clotting disorders.
I now want to introduce platelet transfusions.
These have been incredibly important in modern medicine.
We can obtain platelets from two main ways: The first is that
we can take the bags of red blood cell donation
that are given and take out the platelets by
centrifugation and we pull them from different bags
to make platelet concentrate. However,
these days we often get platelets from plateletpheresis.
In this situation, donors come in every few weeks, a
needle is popped into one of their veins
and blood is taken into a centrifuge, which skims off
platelets and you get a pure platelet fraction.
When do we use these platelets? The normal platelet
count is between 150-400 x 10^9 per liter.
But as you can see there, we really only use
platelet transfusions when the platelet count
falls to a low level perhaps below 5 or 10^9/L.
But again interpret this with caution if the patient
has any problems with bruising or bleeding or infections
at the same time, then we would increase
that threshold and give platelets more often.
But the reason that we do not want to give patients
platelets too liberally is that they don't live very
long and need to be given every 2 or 3 times a week
if the patient is completely dependent.
Also, patients can develop antibodies against platelets
and it can become increasingly difficult to find the correct
donor platelets that don't react with these antibodies.
So, In summary, blood transfusions have been an incredibly
important development in modern medicine
and we would not be able to do many of the procedures
and surgery that we do
without the ability to transfer blood
Blood products can be obtained from classic red cell
donations or from leukophoresis
where patient's blood is taken directly on
to a centrifugation machine.
Donors are carefully screened for the protection
of themselves and the patient
and their blood group antigensare matched with the
patient before any products are given.
There are risks with transfusion including
infection and hemolysis,
but really we've now got those to the very
lowest level that we can,
and the vast majority of blood donations
are now entirely safe.