What are the Risks of Blood Transfusion? Is Your Consent Truly Informed?

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What are the Risks of Blood Transfusion? Is Your Consent Truly Informed?


Most of us have learned that blood transfusion is generally regarded as safe. Yet there is increasing evidence that it increases morbidity and mortality. Transfusion is a predictor of infection, cardiac, renal, respiratory, and neurologic morbidities with a dose dependent effect. It is also a predictor of mortality at 6 months and 5 years follow up. It is associated with increased ICU and hospital length of stay and hospital readmission rates . Despite these associations, and due to the fact that many patients requiring transfusion have co-morbid illness, transfusion practice has escaped much of the scrutiny that evidence based practice demands.

Some of the more common and well-defined risks include a 1/13 chance of alloimmunization to any antibody in red blood cells.  This can complicate future transfusions and create high risk situations in pregnancy.  There is a 1/20 chance of fever, hives, or itchiness.  There is a 1/100 chance of developing heart failure. [1] Thankfully, the infectious risks that we know about are becoming extremely rare.  Unfortunately, in every era transfusion has been considered safe; the risks only become apparent once the harms have been done.  (An article published in 1954 on the safety of blood had no idea that hepatitis and HIV would be transmitted to millions of people in the 1980’s and 1990’s)[2]

In fact when reviewing transfusion history, it is an intervention of trial and error.  The first transfusion from a lamb killed the patient.  In the 1800’s we transfused milk.  From the mid 1800’s we transfused blood, killing approximately 25% of patients until ABO compatibility was discovered in 1907.  Rh incompatibility continued until 1940.  In 1981 HIV was discovered, but the blood supply was not screened until 1985, and a more accurate test was not in place until 1992.  West Nile Virus was discovered in 2002, but the FDA approved screening test was not in place until 2005.[3]  Currently there are numerous known infectious agents that are not screened for including: Zika virus, Parvovirus, hepatitis E, and tick borne illnesses including ehrlichioisis, babesiosis, and borrelia (lyme)[4].  With the exception of parvovirus (1/5000 transfusion transmission risk) the remainder are statistically unlikely to be transfused (unless the baseline donor incidence increases) and the costs go up with every screening test introduced.

The optimist says, “At every juncture we learned and improved,” while the pessimist says, “Transfusion has introduced more harm than benefit.”  The realist says, “Most of the time stay away from transfusion.  When an entire blood volume is actively being lost, it is time to transfuse.”

Even the purported benefit of transfusion has been called into question.  Most of us learned that the delivery of oxygen was more or less linear in relation to total hemoglobin.  In multiple clinical trials, however, oxygen delivery as accounted for by tissue pH or lactate did not show the expected improvement despite increasing hemoglobin levels[5][6][7] [8].  A recent updated mathematical model on tissue oxygenation demonstrated no increase in delivery of oxygen until the hemoglobin was below 58g/L.  The reason?  The higher hematocrit and viscosity associated with transfused blood decreased overall blood flow[9]

But wait... When I give blood, my patient’s heart rate and blood pressure improve.  How can this be possible?  It may actually be simple fluid mechanics of higher viscosity.  This may have benefit in some scenarios, but in the hemodynamically stable patient with a low hemoglobin there is no evidence of benefit.

The guidelines for Choosing Wisely have been based on this.  Don’t give blood if waiting or another modality (iv iron?) may be just as effective.  Don’t transfuse more than 1 unit of packed red blood cells at a time.  Don’t transfuse for an arbitrary hemoglobin threshold in asymptomatic patients[10]

Submitted by:  Dr. Ryan Lett

[1] Callum, JL, 2016. Bloody Easy 4. 4 ed. Ontario: Ontario Regional Blood Coordinating NetworkLibrary and Archives Canada Cataloguing in Publication.

[2] Davidsohn, I, 1954. Indications and contraindications for whole blood and its various fractions. American Journal of Clinical Pathology, 24 (3), p. 349-64

[3] American Association of Blood Banks, Highlights of Transfusion Medicine History. [Website]

Available from: http://www.aabb.org/tm/Pages/highlights.aspx

[July 6 2017]

[4] Public Health Agency of Canada,Transfusion Transmitted Injuries. [Website]

Available from: http://www.phac-aspc.gc.ca/hcai-iamss/tti-it/risks-eng.php#tab2

[July 6, 2017]

[5] Shah, 1982. Failure of red blood cell transfusion to increase oxygen transport or mixed venous PO2 in injured patients.Journal of Trauma,22 (9), p. 741-746

[6] Mazza, BF, 2005. Evaluation of blood transfusion effects on mixed venous oxygen saturation and lactate levels in patients with SIRS/sepsis.Clinics (Sao Paulo),60 (4), p. 311-316.

[7] Creteur, Jacques and Neves, Ana and Vincent, Jean-Louis, 2009. Near-infrared spectroscopy technique to evaluate the effects of red blood cell transfusion on tissue oxygenation.Critical Care,13 (Suppl 5), p. S11.

[8] Lelubre, Christophe and Vincent, Jean-Louis, 2011. Red blood cell transfusion in the critically ill patient.Annals of Intensive Care,1 (1), p. 43.

[9] Zimmerman, et al., 2017. Posttransfusion Increase of Hematocrit per se Does Not Improve Circulatory Oxygen Delivery due to Increased Blood Viscosity.Anesthesia & Analgesia,124 (5), p. 1547–1554.

[10] Canadian Society for Transfusion Medicine, 2015.Choosing Wisely Transfusion Medicine. [Website]

Available from: https://choosingwiselycanada.org/transfusion-medicine/

[July 6, 2017]