Monday, January 3, 2011

Fluid Choice for Plasma Exchange

Situation: A blood center receives requests for large volumes of group B plasma from two separate hospitals for plasma exchange. The center supplies plasma in three main forms: 1) Plasma frozen within 24 hours (FP24) from male donors and never-pregnant female donors, 2) FP24 from female previously pregnant donors, and 3) As cryo-reduced plasma, made exclusively from male and never-pregnant female donors.

This is based on an actual event that occurred during a period of critical shortage of group B plasma, especially from category 1 above. Further investigation revealed that one of the patients (patient A) had a diagnosis of thrombotic thrombocytopenic purpura (TTP), while the other (patient B) was recently diagnosed with multiple myeloma with hyperviscosity. In both cases, the clinicians involved were asking for plasma from category 1 above (with a presumably reduced risk of transfusion-related acute lung injury or "TRALI").

The blood center discussed the issue with the clinicians involved in both cases. We partially supported the request for FP24 from males/nulliparous females for patient A, but did not support it for patient B. Details follow...

TTP is a well-established indication for the use of frozen plasma (either FP24 or FFP) as an exchange fluid.  TTP is caused by a usually acquired deficiency of ADAMTS13, an enzyme that metabolizes von Willebrand factor (vWF) from "ultralarge" to smaller fragments. The lack of this enzyme leaves vWF in  the ultralarge form; this form of the protein stimulates platelet thrombus formation and damage to the red blood cells, brain, and kidneys. The standard treatment is replacement of the "bad plasma" with plasma containing normal levels of ADAMTS13. The best source is FP24/FFP. In my opinion, plasma from any of the three categories above is acceptable for this patient. That from category 2 (from previously pregnant females) does carry a slightly increased risk of causing TRALI, but the mechanics of plasma exchange, where plasma is given and removed on a rapid basis during the exchange, decreases the likelihood of TRALI substantially. In this setting, a mixture of plasma from category 1 and 2 works just great. Cryo-reduced plasma is acceptable, as well, as this product may help with patients with TTP due to the decreased level of all forms of vWF present.

Most non-TTP indications for plasma exchange (including myeloma), do not require FP24/FFP replacement fluid unless the patient has an underlying coagulopathy. The vast majority of these exchanges utilize albumin as replacement fluid rather than frozen human plasma. The majority of the exchanges in these situations are not done repeatedly over multiple days, and most patients tolerate the lack of coagulation factor replacement without a problem. If necessary, for repeated exchanges, a mixture of FP24/FFP and albumin can be used.

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