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Falls Church, VA
Correspondence to: William S. Lyons, MD, 5601 Seminary Rd, 2214N, Falls Church, VA 22041; e-mail: lyonsmd{at}msn.com
To the Editor:
The article by Looney et al (July 2004)1 argues strongly for a separate and distinct entity for the ARDS-like reaction occurring with the transfusion of blood and blood products (curiously, human serum albumin is not mentioned).1 Although Barnard2 as early as 1951 described four cases, presumably of divers sensitivity reactions to transfusion; only one case had pulmonary edema The pulmonary edema component did not enter the literature seriously until well after the description of ARDS, when the great majority of blood transfusions consisted of packed RBCs and generally large amounts of crystalloid fluid. The authors acknowledge that because of the frequency of the latter association, transfusion-related acute lung injury (TRALI) cannot be diagnosed without a fairly rigorous exclusion of "volume overload." It is clear also from the text the authors are satisfied that volume overload can be excluded by ruling out an elevation of pulmonary artery pressure (PAP) or central venous pressure (CVP). This is not possible with these central pressures, and it is likely therefore that TRALI is overreported, rather than underreported as suggested.
TRALI is a noncardiogenic pulmonary edema, as is ARDS. This, of course, presents the profession with the conundrum alluded to above: volume overload in the form of pulmonary edema is present before either the CVP or PAP rise to abnormal levels. This is possible because the microvascular membrane of the lung and elsewhere is completely and rapidly permeable to infused isotonic fluid.
Imprecise language is a problem here. In clinical use, overload refers to an active (iatrogenic) intervention, and volume refers to the amount of fluid infused. This becomes essentially fluid overload. Fluid overload is an excessive expansion or transfusion of the extracellular fluid space with crystalloid, high in salt content, usually isotonic. Confining overload to the circulatory or "blood" volume requires overtransfusion with whole blood, plasma, and other iso-oncotic products. Although "congestion" on this basis alone was once spoken of, it is a now a rare event.
Until the pulmonary edema associated with the transfusion of packed RBCs and plasma derivatives (TRALI) is reported together with accurate infused volumes of crystalloid and colloid, and concurrent changes in patients’ weights, it is not going to be possible to distinguish ARDS from acute lung injury and TRALI.
References
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