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Whole blood must be separated into its component parts before
transfusion to a patient. There are three blood collection
methods that facilitate this process:
Whole Blood Donation
The traditional way to obtain red cells, platelets, or plasma
for transfusion is to have a donor bleed one pint of whole
blood, by gravity, into a blood bag. Although the blood bag
appears red because of the color of the red cells, it is actually
a bag of whole blood containing red cells, whitish platelets,
and clear plasma. Once the blood center has collected multiple
bags of blood, it then takes them to a processing laboratory.
There, the blood bags are put into a washing machine sized
centrifuge, and while the centrifuge is spinning, whole blood
separates into its components parts. After the separation
the bags are squeezed by hand, red cells in one bag, platelets
in another and plasma in a third. This is a time consuming,
labor intensive process with opportunities for error because
so much of it is done by hand and visual inspection.
It is also important to know that one pint of whole blood
contains:
- one transfusible dose of red cells
- one-half to one transfusible dose of plasma; and
- one-sixth to one-eighth dose of platelets (meaning that
six to eight platelet components from whole blood donations
must be combined to make one transfusible dose; these
are known as “pooled” platelets)
Automated Blood Donation
The high tech way to collect blood components eliminates
the need to separate whole blood at a remote laboratory.
Instead, the separation is performed on-line while the blood
donor is attached to the blood collection machine. In this
real time separation method, whole blood is drawn by a pump
into a machine which holds a blood processing chamber that
acts as a mini centrifuge. We refer to this chamber as a
“bowl.” The bowl sits inside the Haemonetics machine you
see pictured here.
As the bowl spins, the whole blood separates. However,
unlike the manual collection method, the machine keeps only
the blood component(s) it is programmed to collect, and
the rest of the blood components are returned to the donor.
This method allows blood collectors the flexibility to maximize
a donor’s gift, taking the component that is most needed
and leaving unneeded components with the donor. In fact,
using this method, blood centers can collect up to two transfusible
doses of red cells, which is a critical advance in blood
collection for reasons which will be reviewed.
Surgical Blood Salvage
Surgical blood salvage allows red cells that have been
lost by a patient undergoing surgery or even after surgery
to be salvaged, washed, packed, hung on an IV pole, and
transfused right back to the patient. This is called surgical
blood salvage, or IAT, “Intraoperative Autologous Transfusion.”
Surgical patients who need blood often prefer to receive
a transfusion of their own red cells for the obvious reason
that their own blood will never transmit the disease of
another blood donor, the blood is fresh, available, and
the correct blood type.
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