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Indications for transfusions 

Transfusions to restore red blood cells (RBC).

It is not possible to specify a clear hemoglobin or hematocrit concentration below which it is necessary to perform a RBC transfusion. This hematocrit or hemoglobin value, called “trigger” (transfusion trigger), has numerous variables among which we mainly find the speed of appearance of anemia and the process that causes it. Before performing a transfusion, we must assess the body's ability to regenerate anemia. As the body needs several days to compensate for blood loss, patients who suffer from anemia due to acute hemorrhage will need blood transfusions with higher hematocrit or hemoglobin levels than others who suffer from more chronic processes, such as chronic kidney failure.
Blood transfusion should not be performed only based on hematocrit and hemoglobin values, but the existence of symptoms of anemia must also be considered. These symptoms include tachycardia, weakness, tachypnea, syncope, and increased lactate levels.

In patients with respiratory or cardiac problems, it may be necessary to perform a transfusion at higher hematocrit or hemoglobin concentrations due to lack of oxygenation of the hemoglobin or the inability of the heart to increase its output. In the case of acute bleeding, red blood cells do not have time to increase the synthesis of the enzyme 2,3-diphosphoglycerate, which increases the passage of oxygen to the tissues. This implies that, in these acute cases, the appearance of anemia symptoms will occur sooner than in chronic processes.

It is also important to assess the pathology that is causing the anemia and the viability of the bone marrow to regenerate it. If the anemia is regenerative and the patient is stable, we can dispense with the transfusion and wait for it to regenerate on its own.
Thus, in cases of acute hypovolemic anemia, it would be indicated to transfuse at hematocrit levels of 20%, while in chronic cases the trigger would be around 12-15%.


Albumin transfusions.

Albumin is a protein synthesized by the liver and responsible for maintaining the oncotic pressure of the blood, among other functions. Its deficiency produces the appearance of edema, delayed healing, altered drug availability, hypercoagulable states and nutritional intolerance. An albumin transfusion is indicated when plasma levels are below 1.5-2 g/dl.

Albumin transfusions can be performed from plasma, with the drawback that large quantities of plasma are necessary to increase the albumin concentration (45ml/kg of plasma to increase the concentration by 1g/kg). This makes it an unviable option. An alternative is to combine these plasma transfusions with the use of colloids.
Another option is found in human albumin transfusions. These solutions are very concentrated, in our country we find 20% solutions (Grifols® Human Albumin at 20%). With small volumes we can achieve notable increases in albumin concentration. However, its use in dogs is not without risks since we can have anaphylactic reactions, especially after the second infusion. There are several published dosages, we use an initial dose of 2g/kg in one hour and subsequently 0.2 - 0.7 ml/kg/h in continuous infusion until plasma albumin levels greater than 2g/dl are achieved.


Replacement of coagulation factors.

In diseases such as rodenticide poisoning, liver failure, hemophilia, disseminated intravascular coagulation (DIC) or Von Willebrand's disease, the provision of coagulation factors may be necessary to treat bleeding. The product of choice in these cases is fresh plasma or fresh frozen plasma. In the case of fresh plasma, it is very important to use it within 6 hours of obtaining it to prevent coagulation factors from degrading. On the other hand, in the PFC the coagulation factors maintain their effect for a year. In cats it is necessary to perform compatibility tests since they could trigger anaphylactic reactions with the recipient's red blood cells. The dose is very variable but in general an initial dose of 6-10ml/kg/6-8h is administered until the bleeding stops. Another alternative to plasma is fresh whole blood or the use of cryoprecipitates.


Transfusions in thrombocytopenia.

In general, thrombocytopenias do not usually cause bleeding until the count is below 50,000/μl. There are concentrated products such as platelet concentrate, platelet-rich plasma or frozen platelets, but they are not usually available in veterinary medicine. Fresh whole blood is the only product we can find that contains platelets, although the increases it produces are not significant.

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