Complications – Blood Transfusion

00:00 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.

00:23 The first is the immediate IgM-mediated lysis or destruction of the red cells.

00:29 Let me go through that in a little bit more detail.

00:32 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.

00:50 They will destroy them and release that free haemoglobin into the patient's blood.

00:57 That can be very serious, indeed fatal and was a major cause of fatalities from blood transfusions in the very early days.

01:05 The second type of hemolytic reaction is where the antibody is delayed.

01:13 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.

01:46 Fortunately, they are rare. Viral infections such as HIV and hepatitis C can be transmitted.

01:54 Fortunately transmission of HIV was exceptionally rare and remains so to this day.

02:02 There are other infections as well that may be transmitted, but it is now a very rare problem.

02:14 Finally, iron accumulation can occur in patients who have regular blood transfusions.

02:20 I will address that in more detail in a minute.

02:24 Now let us look at how we might use these products. On the right, you will see a classic red cell unit.

02:33 It is concentrated and ready to give to a patient who has anaemia.

02:41 Now I've said in that left-hand column that, typically you might give that for patient who has haemoglobin less than 8 g per liter; but that cut- off needs to be interpreted with caution.

02:54 However, I would make the point that in general the threshold for transfusion has decreased in recent years.

03:05 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.

03:15 The reason for that well as you've seen from this lecture, a blood transfusion is quite complicated and costly to produce.

03:25 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.

03:37 People with aplastic anemia may need frequent transfusions every few weeks because red cells as we know live around 120 days so we need to keep topping them up.

03:51 Now interestingly with any units of blood, there is 200 mg of iron.

03:59 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.

04:17 Now iron can be toxic to a range of tissues.

04:20 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.

04:34 Of course as I've said many times, the major concern with blood cell transfusions is that we get the ABO system matched correctly.

04:46 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.

04:59 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.

05:15 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.

05:32 I now want to introduce platelet transfusions. These have been incredibly important in modern medicine.

05:39 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.

06:01 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.

06:17 When do we use these platelets? The normal platelet count is between 150-400 x 10^9 per liter.

06:29 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.

07:23 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 between individuals.

07:38 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.

07:51 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.

08:07 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.