Description: Although approximately 85 million units of red blood cells (RBCs) are transfused annually worldwide, transfusion practices vary widely. The AABB (formerly, the American Association of Blood Banks) developed this guideline to provide clinical recommendations about hemoglobin concentration thresholds and other clinical variables that trigger RBC transfusions in hemodynamically stable adults and children.
Methods: These guidelines are based on a systematic review of the literature on randomized clinical trials evaluating transfusion thresholds. We performed a literature search from 1950 to February 2011 with no language restrictions. We examined the proportion of patients who received any RBC transfusion and the number of RBC units transfused to describe the effect of restrictive transfusion strategies on RBC use. To determine the clinical consequences of restrictive transfusion strategies, we examined overall mortality, nonfatal myocardial infarction, cardiac events, pulmonary edema, stroke, thromboembolism, renal failure, infection, hemorrhage, mental confusion, functional recovery, and length of hospital stay.
Recommendation 1: The AABB recommends adhering to a restrictive transfusion strategy (7 to 8 g/dL) in hospitalized, stable patients (Grade: strong recommendation; high-quality evidence).
Recommendation 2: The AABB suggests adhering to a restrictive strategy in hospitalized patients with preexisting cardiovascular disease and considering transfusion for patients with symptoms or a hemoglobin level of 8 g/dL or less (Grade: weak recommendation; moderate-quality evidence).
Recommendation 3: The AABB cannot recommend for or against a liberal or restrictive transfusion threshold for hospitalized, hemodynamically stable patients with the acute coronary syndrome (Grade: uncertain recommendation; very low-quality evidence).
Recommendation 4: The AABB suggests that transfusion decisions be influenced by symptoms as well as hemoglobin concentration (Grade: weak recommendation; low-quality evidence).
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The Editorial
Editorials
|
3 July 2012
Indications for Blood Transfusions: Too Complex to Base on a Single Number? FREE
In
this issue, the AABB (formerly the American Association of Blood Banks)
presents a clinical practice guideline for red blood cell transfusion (1).
The guideline nicely reports the risks associated with transfusions,
and I do not want to challenge the conclusions reached by this
distinguished group of experts. Indeed, it would be difficult to argue
with their statement that “On the basis of data from all the randomized
trials, the panel found little evidence to support a liberal transfusion
strategy.” Certainly, ample evidence supports the assertion that, in
general, less may be better when it comes to blood transfusion.
Yet,
considering the supporting evidence and the questions the panel focused
on, I do challenge the strict transfusion triggers provided by the
panel. First, in developing the guidelines, the panel focused more on
blood transfusion and its related problems than on the problems
associated with anemia. In any decision to transfuse, one must weigh the
risks and benefits associated with transfusion against those associated
with anemia. Although blood transfusions have been associated with
adverse outcomes, anemia is also associated with increased mortality
rates (2 - 4).
Second, the quality of blood has improved over the years. In
particular, it is likely (although not definitely proven) that
leukoreduction has helped decrease some of the harmful effects of blood
transfusion (5).
Observational studies in Europe have suggested that transfusion has
become safer over time. For example, blood transfusion was an
independent risk factor for mortality in the ABC (Anemia and Blood
Transfusion in Critical Care) study conducted in 1999 (6) but not in the SOAP (Sepsis Occurrence in Acutely Ill Patients) study conducted several years later (7),
although similar statistical techniques (including multivariable
analyses and propensity scoring) were used in the 2 studies. Third and
most important, the studies evaluating liberal versus conservative blood
transfusion practices have usually addressed the simple question of
number of transfusions, without taking into account particular
characteristics of the patient populations, especially the presence of
coronary artery disease (CAD) and patient age.
Perhaps the most influential of these studies was that by Hébert and colleagues (8),
in which patients were assigned to a restrictive (transfusion if
hemoglobin level <7 g/dL) or more liberal (transfusion if hemoglobin
level <10 g/dL) strategy. Patients in the restrictive group had
similar 30-day mortality rates (and even lower mortality rates in the
subgroup of patients with higher disease severity [Acute Physiology and
Chronic Health Evaluation II {APACHE II} score ≤20] and in patients
younger than 55 years). This well-performed, multicenter study serves as
the strongest basis for the AABB's recommendation of a hemoglobin level
of 7 g/dL as the threshold for transfusion. However, several
limitations of the study warrant consideration. First, it was conducted
more than 10 years ago and blood preservation techniques have improved
since then. In particular, leukoreduction was not in practice when the
study was done. Second, the investigators enrolled only a small fraction
(838 of 6451, or 13%) of evaluated patients, and the study was stopped
early due to slow enrollment. These factors raise questions about the
generalizability of the observations. Reanalyzing the data some years
later, Deans and colleagues (9)
highlighted that 30-day mortality was lower in the restrictive group
than in the liberal group in patients without CAD (16% vs. 25%) but was
higher in the restrictive group among patients with CAD (26% vs. 21%; P
= 0.03). The European SOAP group of investigators initiated but quickly
aborted a study comparing hemoglobin thresholds of 7 versus 9 g/dL,
because too many patients did not meet inclusion criteria and the
enrollment rate was very slow. For example, clinicians were
uncomfortable with the idea of assigning a young trauma patient after
bleeding was controlled to the 9-g/dL group, or an elderly patient with
CAD to the 7-g/dL group. The current AABB guidelines (1)
consider the impact of CAD by providing a weak recommendation that the
transfusion threshold should simply be increased from 7 g/dL to 8 g/dL
for patients with preexisting cardiovascular disease.
The specific AABB transfusion thresholds are provided to help standardize transfusion practice (1).
I believe this approach is too simplistic; basing the decision to
transfuse on hemoglobin levels alone is insufficient. Admittedly, using
such typical symptoms of anemia as fatigue, tachycardia, and dyspnea (or
mechanical ventilation) to help in such decisions is not ideal because
they are common indicators of severity of illness. The use of a low Svo2 (venous oxygen saturation) may be helpful, but this has not been fully established (10).
Transfusion decisions need to consider individual patient
characteristics, including age and the presence of CAD, to estimate a
specific patient's likelihood of benefit from transfusion. The decision
to transfuse is too complex and important to be guided by a single
number.
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This article was published at www.annals.org on 27 March 2012.
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