...indications, utility, limitations, and consequences of red blood cell transfusion, especially in critically ill patients.

* RESULTS Several dozen papers were reviewed, including case series, meta-analyses, and retrospective and prospective studies evaluating the physiological effects, clinical efficacy, and consequences and complications of transfusion of packed red blood cells. Most available data indicate that packed red blood cells have very limited ability to augment oxygen delivery to tissues. In addition, the overwhelming preponderance of data accumulated in the past decade indicate that patients receiving such transfusions have significantly poorer outcomes than do patients not receiving such transfusions, as measured by a variety of parameters including, but not limited to, death and infection.

* CONCLUSIONS According to the available data, transfusion of packed red blood cells should be reserved only for situations in which clear physiological indicators for transfusion are present. (American Journal of Critical Care. 2007;16:39-49)

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Even though it was not widely practiced until well into the 20th century, transfusion of blood or blood products has been a source of great interest for centuries. Although the story is now widely discredited, the earliest blood transfusion is said to have occurred in 1492, when the blood of 3 young boys was allegedly transfused into the dying Pope Innocent VIII. In 1665, British physician Richard Lower reported the first successful dog-to-dog transfusions, and, in 1667, Jean-Baptiste Denis reported successful sheep-to-human transfusions in France. The first well-documented and successful human-to-human transfusion was performed in 1818 by James Blundell, a British obstetrician.

Transfusion of blood and blood components remains an extremely common practice in the United States. The American Association of Blood Banks reports that in 2001 nearly 29 million units of blood components were transfused, including nearly 14 million units of packed red blood cells (PRBCs). (1)

Transfusion of PRBCs is a common practice in the critical care setting. In 1995, Corwin et al (2) reported that 85% of critically ill patients who remained in the intensive care unit (ICU) longer than 1 week received blood transfusions. The mean volume of PRBCs transfused was 9.5 units per patient. More recently, researchers in the CRIT study (3) reported an overall transfusion rate of 44% among patients in the ICU.

Complications of blood transfusions such as transfusion reactions and the transmission of a variety of infectious agents long have been recognized. The widespread and sometimes indiscriminate use of PRBC transfusion has continued, despite a growing body of literature documenting its limitations and describing a broad array of complications associated with its use. In this article we review data addressing these limitations and complications, with particular attention to critical care patients.

Methods

The published literature was searched by using the PubMed database of the National Library of Medicine. To evaluate the effect of PRBC transfusion in different populations of critically ill patients, we selected articles that represented original research (prospective or, more commonly, retrospective in nature) for inclusion in the review.

Background

Data indicate that as many as 95% of patients have a lower than normal hemoglobin level by day 3 of their ICU stay. (4) The causes of this anemia are varied and include blood loss due to the primary underlying abnormality (eg, gastrointestinal bleeding), impaired erythrocyte production, and iatrogenic blood loss due to phlebotomy. The significance of the role of phlebotomy in the development of anemia in ICU patients is underappreciated. Results of a 1986 study indicated that ICU patients lost an average of 65 mL of blood daily as a result of phlebotomy. (5) Mean total blood loss per patient was 762 mL per ICU stay (944 mL if an arterial catheter was in place).

Subsequent studies have shown a slight decrease in the amount of blood taken from patients in the ICU, probably due to increased cognizance of the severity of the problem and the institution of blood conservation strategies in the ICU. (6,7) However, these studies indicated that approximately 41 mL per day of blood loss could still be attributed to phlebotomy in patients in the ICU.

Complications such as infections, immunosuppression, impairment of microcirculatory blood flow, 2,3-diphosphoglycerate deficiency, and an array of biochemical and physiological derangements including hypocalcemia, coagulopathy, hyperkalemia, and hypothermia are associated with the use of PRBCs. Some of these complications are a result of inherent properties of the blood products being transfused; others are a consequence of the storage of the red blood cells.

Historically, infection associated with PRBC transfusion has been attributed more often to occult infection in the donor than to contamination of the blood during collection and storage. Numerous studies published in recent years, however, have documented secondary bacterial infection in patients receiving PRBC transfusions, and these studies are reviewed in detail in the following paragraphs.

PRBC transfusion results in a variety of immunomodulatory effects, often referred to as transfusion-associated immunomodulation. Numerous components of blood have been implicated as agents of transfusion-associated immunomodulation. Recent reviews (8,9) of the immunomodulatory effects of blood provide extensive details on this topic. In support of earlier observations, in 1997 Opelz et al (10) demonstrated a clear benefit of red cell transfusions on renal allograft survival in transplant recipients. With regard to the effect of transfusion on tumor recurrence and outcomes in cancer patients, meta-analyses have not yielded an answer to the question of whether transfusion increases the risk of death or tumor progression in these patients. (11,12)

The effect of storage on PRBCs includes decreased levels of 2,3-diphosphoglycerate with a resultant increase in oxygen affinity and a decrease in the ability of hemoglobin to offload oxygen. Morphological changes in erythrocytes may result in increased fragility, decreased viability, and decreased deformability of the cells as well as the release of a number of substances resulting in such adverse systemic responses as fever, cellular injury, alterations in regional and global blood flow, and organ dysfunction. Transfusion with PRBCs that have been stored for long periods is associated with poorer oxygen delivery than is transfusion with fresher cells. (13-15) Evidence also suggests that the transfusion of older blood (stored >14 days)...

NOTE: All illustrations and photos have been removed from this article.



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