Lecture 22: Blood Loss and Transfusions

why is blood loss a concern?

absolute hypovolemia → decreased CO and DO2 → decreased oxygen perfusion of tissue → development of metabolic acidosis and hypoxia

in mammals, 5-8% of total body weight is used to approximate

blood volume

which domesticated species has the lowest blood volume?

cat

canine total blood volume

86 ml/kg (79-90)

estimating blood loss during surgery

• cotton tipped applicator - 0.2ml

• 1 ml of blood = 1 gram of weight

goals of transfusion

• restore oxygen-carrying capacity → anemia, moderate blood loss

• restore blood volume after severe and acute hemorrhage

• replace coagulation factors

transfusion trigger

concentration of Hgb below which DO2 decreases to the point where anaerobic metabolism starts

what are 3 basic reasons that a transfusion may be needed?

hypovolemia, anemia, and coagulopathy

what Hct is often used as a trigger?

20%

fresh whole blood transfused within 6-8 hours of collection

• provides RBCs, WBCs, platelets, plasma, clotting factors

• typically used for acute hemorrhage or life-threatening thrombocytopenia

fresh whole blood transfused after 8 hours

• becomes stored whole blood

• platelets and coagulation factors are markedly reduced

• split it up into components

packed red blood cells

• indicated for anemic patients that need O2 carrying capacity

• no platelets/coag factors

• some IV volume expansion

fresh frozen plasma

• separate from RBC within 8 hrs with specific anticoagulant

• contains protein/albumin so is excellent for IV volume expansion

• contains coagulation factors

• liquid gold

freezer life of fresh frozen plasma

• 1 year from draw date

• after one year it becomes frozen plasma which is good for another 3 years

• good for volume expansion but lacks coag factors

cryoprecipitate and cryosupernatant

• prepared from fresh frozen plasma stored frozen for up to 1 year

• concentrated source of factors VIII, XIII, vWF, and fibrinogen

• indications → hemorrhage or prophylaxis before invasive procedures in deficiency of vWF and factor VIII

platelet rich plasma

• plasma and platelets separated from RBCs after centrifugation

• contains platelets and plasma

• indications → hemorrhage, prophylaxis before invasive procedure in severe thrombocytopenic or thrombocytopathic disorders

determining volume RBC to administer to dogs and cats

• dogs → ml of blood required = BWkg x 90 [(desired PCV-patient PCV)/donor PCV]

• cats → ml of blood required = BWkg x 70 [(desired PCV-patient PCV)/donor PCV]

• this works out to be 10-40 ml/kg in dogs and 5-20 ml/kg in cats

1 unit of pRBC =

500 ml

pRBCs

approx. 1ml/kg to raise PCV by 1%

whole blood is approx.

2ml/kg to raise PCV by 1%

how fast should blood be given?

whole blood or pRBCs can be given at a rate of 5-10 ml/kg/hr after the initial 30 mins

transfusion logistics

• dedicated peripheral or jugular IV

• use aseptic technique

• do not administer other fluids or medications along with transfusion

• rewarm stored blood to 37-39 degrees celsius using a warm fluid bath

• use a specific filter to remove small clots and debris

• use a fluid/syringe pump designed for use with RBCs

major canine blood antigen is

DEA 1

why is blood typing not required on the first transfusion?

because dogs do not have naturally occurring antibodies

what are the main feline blood types?

A, B, AB

true or false: all cats must be typed prior to transfusion.

true

majority of cats have the blood type

A

type A cats

have natural alloantibodies that will shorten RBC life if type B blood is given

type B cats

have natural antibodies against type A → fatal reaction even if only 1ml of type A blood is given

type AB cats

can receive A or B blood

major crossmatch

performed to detect antibodies in the recipient’s serum that may agglutinate or lyse the donor’s erythrocytes

minor crossmatch

detects antibodies in the donor plasma directed against recipient erythrocytes

what is the gold standard for cross matching?

cross match the donor and recipient prior to each transfusion as there are blood types that have not been recognized and there is not type system for Mik

hemolytic reactions

• most severe, but rare and due to incompatible blood

• feline donor recipients should be blood typed prior to the transfusion

• consider crossmatch in cats

febrile reactions

• any increase of one degree or more within 1-2 hours must be considered a febrile reaction due to white cell, platelet, or plasma protein reactions

• stop transfusion immediately

allergic reactions

• patient reacts to allergens in donor blood - RBCs, platelets, WBCs, plasma proteins

• signs → urticaria, dyspnea, laryngeal edema

• stop transfusion immediately

immediate non-immunologic reactions

circulatory overload, hypothermia, electrolyte imbalance, citrate intoxication (hypocalcemia)

delayed immunologic effects

• delayed hemolytic reaction

• graft vs host → destruction of the delivered product with varying compromise to patient

• post-transfusion bruising

• alloimmunization → antibody formation to donor antigens

autologous transfusions

• administration of patient’s own blood back to patient

• decreased risk of transfusion reaction or transmission of disease

• patient may donate blood preoperatively or it could be collected intra or postoperatively and administered back to patient

xenotransfusions

• transfusion of blood from another species

• emergencies