Indications for Blood Transfusions: Too Complex to Base on a Single Number?
- Jean-Louis Vincent, MD, PhD
+ Author Affiliations
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 < 7g/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 [APACHE II score < 20] and in younger
patients below
55 years of age). 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 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.
Article and Author Information
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Potential Conflicts of Interest: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M12-0692.
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Requests for Single Reprints: Jean-Louis Vincent, MD, PhD, Department of Intensive Care, Erasme University Hospital, Université libre de Bruxelles, Brussels 1070, Belgium; e-mail, jlvincen@ulb.ac.be .
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