When is a transfusion of blood components indicated

Erythrocyte concentrates are transfused to correct the symptoms and signs of a lack of oxygen in tissues that are found in anaemia produced by different causes. There are various causes of anaemia and they depend on the particular factors involved in the lack of oxygen in tissues. Amongst these factors, the following stand out: haemoglobin concentration and its ability to carry oxygen, the effort that the body is capable of making and the flow of blood and oxygen to each organ.

When the concentration of haemoglobin reduces, the body starts (sometimes quickly, sometimes not so quickly) its compensation mechanisms to adapt to the new situation in which the body finds itself in order to maintain tissue oxygenation. However, the body's compensation mechanisms are not always the same, in that other factors come into play such as how quickly anaemia starts to set in, the condition of the heart and the respiratory system, the amount of blood and the patient's metabolic state.

Despite the fact that haemoglobin concentration is one of the most frequently used indicators for evaluating erythrocyte transfusion, there is no universal threshold, given that other factors also need to be evaluated, such as compensation mechanisms and underlying illnesses.

Thus, we can say that the decision to carry out a transfusion must always be made on a case-by-case basis taking all the abovementioned factors into account.

What should the dosage be?

The correct erythrocyte concentrate dosage for a particular patient is that which corrects the symptoms caused by a reduction in the right amount of oxygen in the tissues of the body.

An erythrocyte concentrate is the quantity of red blood cells obtained from a donation of blood after separating out the other blood components. Administering erythrocyte concentrate (EC) to an adult increases their haemoglobin by 1-1.5 g/100ml and haematocrit by 2-3%.

Transfusions of platelet concentrates are usually given to prevent haemorrhage in patients who present with low levels of platelets in their blood or where there is something wrong with their platelets. The purpose is to prevent haemorrhage, but platelet concentrates can also be administered to prevent haemorrhage, for example, prior to surgery or after a cancer patient has had chemotherapy.

Given an indication of platelet concentrates, it is very important to evaluate three things:

• the patient's platelet count and other blood-cell counts and coagulation tests
• the presence of, or risk of, haemorrhage
• the cause of the low platelet count (thrombocytopenia)

A reduction in the platelet count is not, in itself, a reason to carry out a transfusion of platelet concentrates.

Thrombocytopenias: for platelet counts above 50,000 /µ ?l, a transfusion is rarely required except in special circumstances.

What should the dosage be?

In order for the post-transfusion platelet count to increase by about 20,000 / ?l, the appropriate dose for an adult is 3x1011 platelets, in other words, 300 billion platelets.

The quantity of platelet concentrates to be given in a transfusion depends on their origin, i.e. whether they come from:

aphaeresis:or an adult, the usual dosage is one unit
leuko-platelet layers: the usual dosage is one platelet concentrate made up from four or five donations of total blood

In paediatrics: 10 ml of platelet concentrate is administered for every kilo the child weighs.

Frequency of treatment will depend on clinical indications. For prophylactic treatments, one dose every 24-48 hours is normal. In the case of surgical interventions, the transfusion is carried out immediately prior to surgery.

What are the possible side effects?

A platelet transfusion can cause the following side effects (which are more common than with other transfusions):

febrile reactions: although these are less common due to the use of blood components which do not contain white blood cells (leukoreduced)
bacterial contamination: although not common, bacterial contamination occurs more often than with other transfusions, as they are kept at a temperature of 22ºC
alloimmunisation: production of antibodies against different blood components, which could affect the effectiveness of subsequent transfusions

Despite its widespread use, plasma probably has the least-established indications out of all the blood components. Except in specific cases, it is preferable to plasma derivatives, in a concentrated and purified form which can be prescribed in precise doses, inactivated for potentially contaminating viruses. We currently have very efficacious and safe plasma derivatives for the majority of indications.

The risks associated with plasma transfusions include: circulatory overload, destruction of erythrocytes resulting from ABO incompatibility, anticoagulant toxicity, febrile and allergic reactions and a lung syndrome called TRALI which can be very serious.

What are the indications for plasma transfusions?

As in the case of a deficiency in coagulation factors or endogenous anticoagulants, fresh-frozen plasma transfusions are only indicated when the deficient concentrate does not exist or is not available. Indications as to when its use is established and has been demonstrated to be efficacious are as follows.

The possibility of performing plasma transfusions is considered when there is both haemorrhagic syndrome and changes in coagulation test results. The following are some of the situations when these circumstances arise and when they need to be evaluated individually:

• disseminated intravascular coagulation
• in cases of overdose of oral anticoagulants (SintromR, AldocumarR etc.), with life-threatening haemorrhage as well as with patients who have to undergo extremely urgent bloody procedures
• liver transplants
• hepatopathy with diffuse haemorrhaging
• massive transfusions
• cirurgia extracorpòria
• congenital coagulation deficiencies, in the absence of specific concentrate factors