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With
the rapid developments in the field of Medicine and
Surgery, blood transfusions have become an integral
part of hospital procedures. Modern medical practice
increasingly relies on the use of components of blood
such as red blood cells, platelets, granulocytes,
clotting factors, plasma, albumin and so on.
Transfusion Technology has undergone tremendous
changes from the latter part of the 19th Century.
Notable advances have been made in the detection of
bacterial and viral contamination in blood and blood
products and for their inactivation, development of
sophisticated filters for the removal of leucocytes
and other blood components and in apheresis
technologies which is a fast developing field with
great possibilities.
Yet
another development which will have great impact in
the technology of blood bags and medical products is
the likely replacement of the phthalate plasticizers
such as DEHP, which have certain undesirable effects,
with non-phthalate plasticizers.
Interest in the field has been rapidly growing. The
countries of the European Union have been particularly
active in this field and have developed DINCH
plasticized blood bags for the storage of RBCs,
platelets and blood plasma.
M/s.TerumoPenpol
has been a pioneer in this field since 2002. They have
shown the possibility of replacement of DEHP with the
BASF plasticizer HexamollDINCH for the collection and
storage of whole blood. RBCs, Platelets and blood
plasma. Another non DEHP plasticizer which has shown
promise for the storage of blood and blood components
in studies conducted at Terumo Penpol is Di-Octyl
Terephthalate (DOTP).
The
Introduction of plastic bags for the collection of
blood and blood components
The
first blood bag was invented by Dr. Carl Walter in
1947 which was made using poly vinyl chloride polymer
plasticized with dioctyl phthalate (actually di,
2-ethyl hexyl phthalate - DEHP). The selection of this
plasticizer was an uncanny achievement bordering on
the miraculous because of its excellent plasticizing
characteristics for PVC which conferred most desirable
physical characteristics and ability to enhance the
storage quality of blood and more particularly the red
blood cells. DEHP remains the plasticizer of choice
even now.
The
collection, separation and administration of blood and
blood products were done exclusively in glass bottles
till the year 1970, even though PVC plasticized bags
were used experimentally during the Korean War in
order to prevent wastage of blood stored in glass
bottles during air dropping operations to forward
areas.
Benefits of DEHP Plasticized PVC Containers for the
Collection and Storage of Blood and Blood Components
Plasticized PVC containers have a number of advantages
which makes it ideal for the medical and more
particularly for blood contact applications. The
plasticizers used in the compounding of PVC plays the
main role for building in the desirable
characteristics such as low toxicity, transparency,
flexibility, mechanical strength, elongation,
stability at low and high temperatures, permeability
to water, oxygen and carbon dioxide. A wide range of
plasticizers do meet these requirements, for food
contact, and medical devices. For contact with blood
and blood products,
however, the choice of plasticizers is very much
restricted. The
plasticizers Di, 2-ethyl hexyl phthalate (DEHP) offers
all the benefits of overall performance, ready
availability at high purity levels and cost
effectiveness. DEHP
has the unique ability to reinforce red blood cell
membranes, thereby reducing the development of
brittleness on storage and consequent lysis of red
blood cells. This remarkable protective effect seems
to be a characteristic of phthalates in general.
Possibly, the structure of phthalate with a
hydrophilic aromatic ring and two hydrophobic tails
enables them to replace defects in the RBC bilayer
skin consisting of phospholipid molecules which are
characterized by a hydrophilic end group with two
hydrophobic chains.
Recent
observations, however, seem to indicate that the
harmful effects of DEHP may, in fact, be due to the
mono ethyl hexyl phthalate (MEHP) which is formed by
the hydrolysis of DEHP during processing.
The
Leaching of DEHP into Blood and Blood products
DEHP is
not covalently bonded to PVC and so could migrate out
of the plastic into aqueous media particularly in the
presence of solubilizing lipids, lipoproteins and
albumin. In 1970 Jaegar and Rubin reported that DEHP
leached into blood and blood products, when these were
stored within blood bags plastized with DEHP.
This
observation caused an avalanche of studies on the
effect of the leached plasticizer on patients and
possible harmful effects therefrom. There are over
3000 research papers covering every aspect of this
problem. Very comprehensive and critical assessments
on the massive research data and information available
for vulnerable groups of people have been made. The
present position is that the DEHP leached out from
medical devices is of concern particularly to prenatal
male babies, male new borns, young males and patients
who need frequent blood donations and/or dialysis
including exchange transfusions or extra corporeal
membrane oxygenations.
Storage of Platelets
The
metabolism of platelets, unlike that for RBC, follows
a predominantly aerobic pathway. Hence containers for
their collection and storage should have higher
permeability to oxygen and carbon dioxide. Platelets
can be stored with reasonable post transfusion
recovery and survival for upto 72 hours in DEHP
plasticized PVC bags. DEHP is not considered the best
plasticizer for platelet storage bags. Non DEHP
containers such as TEHTM, BTHCplasticised PVC
containers and modified Poly olefin containers
(Baxter) are preferred for better efficiency of
storage.
Storage of Blood Plasma
Blood
Plasma contains over ten million immunoglobulins and
thousands of plasma proteins. Plasma proteins are
needed for patients suffering from antibody
deficiencies and hemophiliacs.
Frozen
plasma is a stable product which can be stored for ten
years. It can also be stored in dry form. Blood plasma
should be collected and stored in containers which
donot have leachable materials such as DEHP.
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