Physiology of Transfusion Therapy

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Physiology of Transfusion

Therapy

Vithal V. Vernenkar, D.O.Dept. of Surgery

St. Barnabas Hospital


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Indications for Transfusion Enhance oxygen carrying capacity of blood

by expanding red call mass.

Replace clotting factors, either lost,

consumed, or not produced.


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Enhancement of Oxygen

Carrying Capacity Majority of arterial blood oxygen binds

with hemoglobin reversibly.

Release of O2 to tissues depend on many

factors, the oxygen saturation being the

most important.

The saturation of hemoglobin molecules

with O2 determines the binding affinity.


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Enhancement of Oxygen

Carrying Capacity As saturation increases, affinity decreases, release

of O2 to tissues is then enhanced.

The partial pressure of O2 required to saturate50% of the Hb molecules is called P-50.

P-50 value is increased with fever, acidosis,increased 2,3 DPG, thus O2 is released to tissues

with greater ease under these circumstances. However with hypothermia, alkalosis, and

decreased 2,3 DPG affinity is increased, releasedecreased.


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O2 Carrying Capacity Tissue oxygenation also depends on tissue

oxygen demands.

Under normal circumstances, there is aphysiologic reserve between O2 delivery

(1000cc/min) and consumption (250cc/min).

Despite this large reserve, clinical circumstances,such as massive MOSF, can have consumption

outstripping delivery.


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O2 Carrying Capacity Hb normally ranges between 12-18g/dL

depending on race, age, sex, medical condition.

Old tradition of keeping Hb at 10 is not valid. A Hb of 7-8 has been demonstrated to be

adequate except in patients with CAD, COPD.

It is clear that the rate and magnitude of blood

loss, state of tissue perfusion, pre-existingcardiopulmonary disease all affect the ability ofthe patient to tolerate lower concentrations of Hb.


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O2 Carrying Capacity Decreased levels of 2,3 DPG increase O2-

Hb binding affinity.

2,3 DPG levels may decrease by 30% inblood stored for greater than 2 weeks, by60-70% in 3 weeks.

When transfused, this old blood has asignificantly diminished ability to releaseO2 to tissues.


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Enhancement of Hemostasis Replacement products should be used only

in preparation for elective surgery, or with

clinically significant abnormalities in

hemostasis.

These include disorders of consumption or

production of fibrinogen, intrinsic orextrinsic factor defects, platelet

dysfunction.


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Packed Red Blood Cells Prepared by removing 200 cc of plasma

from fresh whole blood, to achieve a final

HCT of 70-80%. They are kept anticoagulated with CPD

(citrate, phosphate, dextrose), stored in

liquid state at 4 degrees or frozen at80C. The longer the storage, the lower the rate of

survival. Immediate (90%), 6 weeks (65%).


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Cryopreserved RBC This technique utilizes rapid cooling of

PRBC to80C in 40% glycerol, post

transfusion survival is 80-90%, 2,3 DPGlevels are normal, antigenic reactionsminimized.

Large quantities of red cells can be storedfor many years.

Kind of expensive!


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Autotransfusion Involves collection and immediate reinfusion of

patients own blood for volume replacement an d

to increase red cell mass. Massive exsanguination from either blunt or

penetrating trauma without gross enteric

contamination best candidates.

Eliminates risk of histocompatability reactions,

infectious disease.


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Autotransfusion Not without risk, most common

complication is thrombocytopenia.

When patients receive more than 4L ofblood, platelet count may drop to less than50,000, risk of ATN increased from debris

of plasma-free Hb. Also risk of air embolism, particulate

microemboli, DIC.


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Pre-Donation Increased with public awareness of

transmission of infection with blood

transfusion. Blood storage in pre-donation is similar to

PRBC (42 day maximum).

Contraindications include significant CAD,COPD, existence of a hematologicdisorder.


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Products That Enhance

Hemostasis Fresh Frozen Plasma-Single donor, same

risk of HIV, Hepatitis as PRBC.

Frozen at 8C, this temperature protects

Factor V and VII in particular.

FFP contains components of the

coagulation, fibrinolytic, and complement

systems.


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Products That Enhance

Hemostasis Useful in treating deficiencies in

2,5,7,8,9,10,11. Also in Coumadin reversal,

ATIII deficiency.

Type and Rh specific plasma should be

used.

Urticaria, fatal pulmonary edema.


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Cryoprecipitate Used to replenish Factor VIII or fibrinogen.

Formed as a plasma concentrate that consists

primary as Factor VIII and fibrinogen. In addition it contains Factor XIII, vWF,

fibronectin.

Stored at 37C. Above this Factor VIII destroyed.

Disadvantage is multiple donors, increased risk ofhemolytic reactions due to small amts of anti-A,anti-B, and Rh antibodies left over in preparation.


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Platelets Collected by repeated centrifugation of fresh

whole blood, and suspension in 30-50 cc of

plasma at 22C. Remain viable up to 5 days, most efficacious if

used within 24-48h of pooling. After that loseability to produce thromboxane A-2, a potent

vasoconstrictor and platelet aggregator. Risk of infectious complications equal to number

of donors, must be ABO and Rh compatible,since donor plasma is present.


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Complications of Transfusion Immunologic reactions

Metabolic reactions

Infectious complications


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Immediate Hemolytic Reactions ABO incompatibility most commonly

caused by sample labeling,

misidentification.

Reaction soon after transfusion started.


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Immediate Hemolytic Reactions Change in mental status, SOB,

hypotension, back pain, chest pain, facial

flushing, cyanosis, tachycardia, profound

shock. Can end in DIC, acute renal failure,

death. Normally haptoglobin is capable of

binding free Hb in plasma. The complex isthen cleared by reticuloendothelial system.

If this clearance mech is exceeded.


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Immediate Hemolytic Reactions Renal failure produced by free hemoglobin

bound to albumin to form methalbumin.

Hemoglobinuria occurs, hypotension andvasoconstriction cause a reduction in GFR,thrombi form in renal tubules.

Circulating antibody complexes released into circulation make renal failure worse.

In OR may present as diffuse bleeding.


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Delayed Hemolysis Infrequent, related to red cell antigens other

than A or B.

Can occur 3-21 days after blood is infused.

Symptoms include malaise and fever.

Labs show low Hb, elevated indirectbilirubin.

Usually observe if stable.


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Allergic Reactions Transfusion of antibodies or antigens to

which the recipient is sensitive.

Urticaria, chills, itching, fever.

Occurs frequently, 2% of transfusions.

In rare occasions, can cause anaphylacticshock.


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Febrile Reactions Most common transfusion reaction (7% of

transfusions.).

Due to antileukocyte antibodies that develop as aresult of prior transfusions.

Fever, chills, flushing, tachycardia.

May progress to hypertension, cyanosis, collapse. Rule out bacterial contamination and ABO

incompatibility when it occurs.


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Anaphylactoid Reactions When recipient is sensitized to IgA, a

common immunoglobulin.

Fever, chills, bronchospasm, diarrhea,

abdominal pain, vascular collapse.

Transfusion related acute lung injury- Rare,

caused by antibodies to recipients WBC,

clot in pulmonary circulation.


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Bacterial Contamination All blood products except albumin and

serum globulins carry HIV and Hepatitis

risk. Thats because they are heat treated.

19% of all fatal reactions involve blood

products with contamination.

1-2% of all blood products may be

contaminated with bacteria.


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Bacterial Contamination Most common cold growing, endotoxin-

producing, gram negative organisms are

klebsiella, pseudomonas, identified in 68%

of the reported reactions. Gram positive

organisms responsible usually staph.

Contamination arises from donor. Hypotension, fever, abd pain, extremity

pain,sepsis.


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Bacterial Contamination Onset shortly after transfusion begins, temp

spikes at 12 h intervals.

Absence of hemoglobin in urine and presence ofbacteria in the blood product confirms diagnosis.

Mortality 50-80%.

Most common blood product cause ofcontamination is plateletsnot refrigerated.


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Viral Contamination Hepatitis most common. 2.5-8% risk per unit.

Most common is Hepatitis C (85-98%),

incubation 8 weeks, chronic in 50% of patients.

HIV risk 1: 1,000,000- 2,000,000 per unit blood.

CMV, EBV especially in premature infants,

transplant patients.


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Other Problems Citrate- causes hypocalcemia, also direct

cardiac depressant. From massive rapid

transfusions of PRBC.

Replace calcium 1 gram for each 6 units

transfused, since in a trauma scenario,

checking ionized Ca not practical


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Other Problems Hypothermia, coagulopathy, leftward shift in O2

dissociation curve, less release.

Dilutional thrombocytopenia, after transfusion ofmore than 10 units blood.

Hyperkalemia- as a result of ADP pump

inactivation in stored blood, potassium levels can

reach 70 meq/L. Watch out in renal patientsNot

really a problem though.


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Physiology of Transfusion Therapy

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