AssessmentsBlood products and transfusion: Clinical practice
USMLE® Step 2 style questions USMLE
A 35-year old male is to undergo heart surgery and will be placed on cardiac bypass. He is anticoagulated with unfractionated heparin prior to and during bypass. At the end of the procedure, the patient is weaned off the cardiopulmonary bypass by warming, lung ventilation, and heart defibrillation. The venous return of the bypass machine will be slowed down, allowing the heart to fill and the external pump to be decelerated. While this is occurring, global cardiac function and hemodynamics must be monitored. Finally, anticoagulation must be reversed and hemostasis achieved. What should be used to achieve this?
Content Reviewers:Rishi Desai, MD, MPH
Blood transfusions are life-saving treatment options, to the point where informed consent is not necessarily required if it has to be done in an emergency to save a person’s life.
Additionally, blood banks have developed a sophisticated variety of blood products to ensure that they’re free of infection and compatible with a recipient’s blood type.
To understand them all, let’s review the normal components of blood. When blood is spun down in a centrifuge, the layers separate out.
The first layer is the cellular component, which accounts for 45% of blood, and includes red blood cells, or RBCs, white blood cells, or WBCs, and platelets.
Second is the acellular component, also called plasma, which accounts for 55% of blood.
Plasma is composed of everything that isn’t a cell, including proteins like albumin, electrolytes like sodium, molecules like glucose, coagulation factors like factor 8, and lipoproteins like low-density lipoprotein, or LDL.
Now, the main blood products that can be transfused are packed red blood cells, or PRBCs, which are RBCs that had most of their surrounding plasma removed, fresh frozen plasma, or FFP, which is made of all the coagulation factors together, platelets, prothrombin complex concentrates, or PCCs, which are composed of factors 2,7,9 and 10, cryoprecipitate, which is made of fibrinogen, von willebrand factor, and factors 8 and 13 and finally pure coagulation factor concentrates, like pure factor 8.
Alright, so acutely bleeding or anemic patients can require PRBC transfusions.
To do that, a sample of their blood is taken, and the bank performs a “type and screen”.
Type refers to looking at the recipient’s RBCs surface antigens, which include their ABO, Rh or D-antigens and checking if they’re compatible with the donor’s RBCs.
Screen refers to looking for antibodies in the recipient’s plasma, and if they’re present, then making sure that the donor RBCs don’t have antigens that would get bound by those antibodies. This is done to prevent a transfusion reaction.
If the donor and recipient are compatible, the PRBC transfusion is given.
On average, one unit of PRBCs increases the hemoglobin concentration by 1 gram per deciliter, and generally, the goal is to keep the hemoglobin above 7 g/dl.
In emergencies, group O negative blood is considered a universal donor, and can be transfused to anyone.
That’s because group O negative blood has no antigens on the RBC surface, so there’s no risk of incompatibility.
Usually, platelets are transfused when the platelet count goes below 10,000 cells per millimeter square in an asymptomatic patient, or below 50,000 if the patient is actively bleeding or will have a procedure, like a lumbar puncture.
Prothrombin complex concentrates or PCCs contain factors 2,7,9 and 10, and are much faster in onset compared to FFP.
Therefore, PCCs are used in life-threatening warfarin-induced bleeding, like an intracranial hemorrhage.
Cryoprecipitate is composed of fibrinogen, von willebrand factor, and factors 8 and 13.
Because specific concentrates are now widely available, cryoprecipitate is seldom used clinically, but can be used in DIC to replace the depleted fibrinogen, or in factor 13 deficiency.
Some of the filtered blood components are removed, and the rest of the blood returns to the patient.
Alright, now transfusions can cause a lot of potential complications, some of which are life-threatening. We can generally divide them into non-immune mediated and immune mediated complications.
Kicking off with the non-immune mediated complications. Blood transfusions risk transmitting infectious microorganisms The most common ones - in descending order are cytomegalovirus, or CMV, which can occur once every 100 transfusions, hepatitis B, which occurs about once every 200,000 transfusions, and hepatitis C and HIV, both of which occurs about once every 2 million transfusions.
These numbers vary quite a bit depending on the healthcare setting because the way blood is screened differs around the world.
Because CMV infects white blood cells, one common method of preventing it is by removing the white blood cells from the product, a process called leucodepletion.
Also, platelets are typically stored in a warm environment, which also provides a nice temperature for bacteria to grow.