Therapeutic plasmapheresis

The following processes can be described as selective therapeutic plasmapheresis. In a first step, blood is withdrawn from the patient and separated by crossflow filtration in a hollow-fiber membrane cartridge water and some plasma solutes are transferred through a semipermeable membrane under a convection process. The transmembrane pressure applied from blood to filtrate compartment ensures flow and mass transfers. Then, the filtrate perfuses the adsorption columns where toxins are retained and is finally mixed with blood cells and other plasma components before returning to the patient (Figure 18.11). 

Apheresis procedures are considered to be relatively safe when performed by experienced personnel. However, they are not without dangers, and there are some health risks to both patients and donors. Not unexpectedly, the risks are greater with therapeutic plasmapheresis on account of the underlying disease, with an estimated 3 deaths per 10 000 procedures (2). 

Yildirim C, Bayraktaroglu Z,Gunay N,et al.The use of therapeutic plasmapheresis in the treatment of poisoned and snake bite victims an academic emergency department s experiences. J Clin Apher. 2006 21 219-223... 

The need to transfuse blood components such as plasma, platelets, factor VIII, in addition to red blood cells (RBC) has generated the development of plasmapheresis (plasma separation from whole blood) and more generally that of apheresis (fractionation of blood components). Plasma collection from donors by centrifugation of blood bags began only in 1944. This technique was extended to therapeutic plasma purification in 1950, but RBCs were fragilized by the centrifugation and the plasma was not completely platelet-free. 

Plasmapheresis is an intermediate form of therapy for myasthenia gravis, having effects that last longer than those of cholinesterase inhibitors but shorter than those of thymectomy. Improvement in myasthenic symptoms often occurs, but its duration is unpredictable. Plasmapheresis usually is reserved for patients who have severe symptoms resistant to other therapeutic approaches or for patients preparing for thymectomy. 

Therapeutic plasma exchange (TPE), or plasmapheresis (PP), is an extracorporeal therapy most frequently used in the treatment of hematologic disorders, and autoimmune neuropathies and vasculitides [37]. This modality occasionally is also employed in the treatment of poisoning. The apparatus involves central venous access and a blood circuit between the patient and a pheresis machine. Cytopheresis by centrifugation or filtration then separates the formed elements of blood from plasma. The cells are returned to the patient while the plasma (with the poison) is discarded. Fluid volume is typically replaced with crystalloid, colloid, or fresh frozen plasma (FFP) if clotting factor repletion is necessary. 

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