General Requirements for Blood Bags and Platelet Storage Bags
After extensive studies of blood bags, platelet storage bags,
and bags made with sheets manufactured by reputed manufacturers as suitable for
blood bags and platelet storage bags, we have arrived at the general
requirements for blood collection bags (Main bags) and platelet storage bags.
These are given in table-1.
The dimensions of blood bags of different manufacturers vary and so the total
internal surface exposed to blood/blood components also vary. There is also
variation in the thickness of the blood bag sheet material. Considering these
factors, a proper comparison of the permeability of blood bags should be based
on the permeability per bag for 24 hours. These figures
are also given in the table. The permeability requirements for oxygen for
platelet storage bags is about 30% higher than for the main bags. In the case of
carbon dioxide, platelet bags need around 16% more permeability than for main
bags. The factors which affect the permeability of PVC bags are:
-
The level and nature of plasticisers;
-
The level and nature of other additives;
-
The thickness of the sheet; and
-
The surface area of bags.
Control of these factors permit PVC sheet of different permeabilities to be obtained.
Table-1: The General Requirements for Blood Bags and Platelet Storage
Bags
|
| S.
No. |
Characgteristics
of blood bag sheet |
Main
bags |
Platelet
storage bags |
| 1 |
Hardness
(Shore A) |
72
+ 5 |
69
+ 3 |
| 2 |
Thickness
(mm) |
0.39
+ 0.03 |
0.38
+ 0.02 |
| 3 |
Tensile
Strength (kg/cm2) |
165.5
+ 2.5 |
173
+ 7 |
| 4 |
Elongation at
break (%) |
380
+ 30 |
365
+ 15 |
| 5 |
Permeability
to water (g/m2/24h) |
16.15
+ 2.15 |
17.4
+ 1.4 |
| 6 |
Permeability
to oxygen (ml/m2/24h) |
685
+ 165 |
1165
+ 385 |
| 7 |
Permeability
to carbon dioxide (ml/m2/24h) |
4160
+ 1040 |
6050
+ 1700 |
| 8 |
Extraction
with water (%, 90oC, 24h) |
0.053
+ 0.018 |
0.05,
0.075 |
| 9 |
Extraction
with soapy water (%, 90oC, 24h) |
3.05
+ 0.65 |
V.
low, 3.20 |
| 10 |
Permeability
to water/bag (g/bag/24h) |
0.67
+ 0.08 |
0.67
+ 0.09 |
| 11 |
Permeability
to oxygen/bag (g/bag/24h) |
28.3
+ 6.6 |
36.5
+ 8.5 |
| 12 |
Permeability
to carbon dioxide/bag (g/bag/24h) |
171.5
+ 41.5 |
194
+ 44 |
|
A Single Formulation for Blood Bags and Platelet Storage Bags
BTHC plasticised PVC bags have been shown to be suitable for
the storage of blood, red cell concentrates and platelets. This PVC material has
comparatively very high permeability for carbon dioxide (upto 17,000 ml/m2/24
h.) and so difficulties have been experienced for the storage of platelet
concentrates having high platelet levels.
TOTM plasticised bags and modified polyolefin bags are suitable for the
storage of platelets but not for the extended storage of whole blood or red cell
concentrates.
Our studies have shown that
DEHP plasticised PVC could be used for the main bags as well as for platelet
storage bags. As has been indicated earlier, by varying the plasticiser level,
the quantity and nature of additives, sheet thickness and size of bags, it is
possible to obtain PVC in a wide range of permeabilities. If a single PVC
compound is desired for main bags and platelet storage bags, the choice of DEHP
level is limited. The desired range of permeabilities for platelet storage bags
could be achieved by the use of thinner sheets and larger size for bags. As
regards thickness of sheets 0.35 – 0.42 mm is most desirable considering
strength characteristics, freedom from pinholes and other defects. PVC sheets of
less than 0.35 mm are liable to develop more defects. TERUMO PENPOL has
developed formulations based on DEHP suitable for storing whole blood and
platelets.
Use of a single formulation
based on DEHP has a number of advantages:
-
DEHP is the lowest priced plasticiser available in
commercial quantities at very high purity levels.
-
A single formulation reduces the inventory of materials.
-
Studies have already shown that DEHP plasticised bags have
no deleterious effects on platelets other than a slight reduction in
aggregation due to the stabilisation of platelet membranes.
-
Platelets have very low adhesion to DEHP plasticised PVC
sheets as compared to TOTM and BTHC (table-2).
Table-2: Adhesion of Platelets to
Polymer Surfaces
|
| Material |
Plasticisers/Additives |
Rel.Platelet
Adhesion Percent |
Baxter
Code |
| Teflon |
Unplasticised |
110.0 |
|
| Polystyrene |
Unplasticised |
826.0 |
|
| Polyolefin |
Antioxidant |
77.2 |
PL
732 |
| PVC |
TOTM |
20.2 |
PL
1240 |
| PVC |
BTHC |
3.8 |
PL
2209 |
| PVC |
DEHP |
2.9 |
PL
146 |
|
| (Ref:
Transfusion: 1992, 32 (Suppl.) 68S |
Blends of Plasticisers
PVC plasticised with blends of plasticisers have been studied
for platelet storage of TERUMO PENPOL. By blending DEHP with TOTM it is possible
to reduce the leaching of DEHP and also platelet adhesion to the blood bag
surface.
BTHC blended with TOTM enables the high carbon dioxide
permeability levels to be brought down to more acceptable limits.
Blood bags made with PVC sheets plasticised with different
plasticisers have been under study at TERUMO PENPOL. There are various
possibliities:
-
The use of DEHP and TOTM plasticised sheets could reduce
the DEHP leaching of main bags.
-
Use of BTHC and TOTM plasticised sheets could reduce the
leaching of BTHC and also reduce overall carbon dioxide permeability of bags
to desirable limits.
|
