Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a disposable cold pack for
cooling and storing a container filled with a sample of freshly
drawn blood for subsequent analysis.
In conducting certain analyses of samples of freshly
drawn arterial blood, it is essential for optimum accuracy to
carry out the analyses without delay, because when the sample is
allowed to stand for more than a few minutes at room temperature,
changes in composition occur which render the subsequent analy-
sis inaccurate. It is frequently impossible to arrange for the
necessary analytical equipment to be present at the location
where the blood sample is drawn and so the practice has devel-
oped of immediately immersing the sample in its container, which
is usually the sealed plastic or glass barrel of a syringe, in a -
bucket of ice or of a water-ice mixture in order to chill it as
rapidly as possible and to maintain it at a temperat~re slightly
above freezing while it is transported in the ice bucket to the
anaIytical equipment. The elapsed time between the drawing of
the sample and t~e beginning of analysis usually does not exceed
45 minutes. It is important that the temperature of the blood
sample be maintained below 40F. after it has been drawn because
changes in composition occur fairly rapidly when the temperature
of the blood sample exceeds that level. On the other hand, it ;
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is essential that the temperature of the sample not be reduced
below 28QF. in order to avoid irreversible changes in cell ;
structure caused by freezing. In the case of an ice bucket,
tests have shown that a period of 7 minutes is required to lower
the temperature of the usual 5 cc. blood sample from body
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temperature (99F.) to 36F. with crushed ice alone (no water),
and 4 minutes with a water-ice mixture, in room temperature
(76F.) surroundings.
Although disposable cold packs such as the one des-
cribed in Robbins et al U.S. Patent 2,925,719 have been available,
they have failed to provide for chilling at maximum rate of speed
without risk of cooling below the critical temperature of 28F.,
while at the same time ensuring a temperature below 40F. for a
sufficiently long period of time. The present invention provides
a disposable cold pack which can readily be activated without
special equipment and which is effective to chill rapidly a con-
tainer filled with a freshly drawn sample of blood from body tem- ;
perature to a temperature within the range from 28 to 40F. and
to maintain it within that temperature range for at least 45 min-
utes. Tests have shown that the preferred embodiment of the
present invention is capable of cooling the usual 5 cc. blood
sample from 99F.to 36F. within 2 minutes in room temperature
(76F.) surroundings. The invention provides a disposable cold
pack for cooling and storing a container filled with a sample of
~reshly drawn blood comprising an outer flexible insulation layer
comprising foam plastic material, a first sealed flexible enve-
lope of plastlc material secured adjacent one face of the insula-
tion layer, a supply of dry, solid ammonium nitrate disposed
within the first envelope, a second sealed and frangible envelope ~-
containing a supply of water disposed within the first envelope ~
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and arranged to be broken by pressure applied externally to the ---
first envelope to release the supply of water into the supply of
ammonium nitrate within the first envelope to activate the cold
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pack, the weight ratio of ammonium nitrate to water being from
1.24:1 to 1.26:1 and a closure member having a pressure-sensi-
tive adhesive face secured to the insulation layer for releas-
ably maintaining the cold pack in folded position with the insu-
lation layer outermost and with the sample container in contact
with the first envelope, the cold pack being capable of chill-
ing the blood sample rapidly and of maintaining it at a tempera-
ture of 28 to 40F. for at least 45 minutes after activation in
room temperature surroundings. In a preferred embodiment, the
insulation layer includes a continuous film of flexible plastic
bonded to the foam plastic material at the face adjacent the
first envelope, and the first envelope is heat sealed along at .: : .
least one marginal portion thereof to the insulation layer. In
the preferred embodiment, the invention further features an
insulation layer of rectangular configuration which is not only
coextensive in area with one face of the rectangular first enve . -
lope but extends substantially beyond at least one margin of the
first envelope to provide a flap, the closure member being -:
secured to the margin of the flap remote from the first envelope.
In the usual case where the size of the blood sample is approxi-
mately 5 cc., the total weight of water and ammonium nitrate
must be from 180 to 200 grams for best results.
Other features and advantages of the invention will
appear from the drawing and from the detailed description which
follows. -
In the drawing~
Fig. 1 is an isometric view showing a preferred embodi- -
ment o the invention before activation and use;
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Fig. 2 is a view in cross-section on an enlarged scale
showing the embodiment of Fig. l before activation and use;
Fig. 3 is a view in cross-section showing the device
after activation with the sample container enfolded within it;
and
Fig. 4 is a view in cross-section taken along line 4-4
of Fig. 3.
The embodiment shown in the drawing includes an outer
generally rectangular flexible insulation layer lO of foam plastic
material such as a foamed polyethylene material sold under the
trademark Microfoam approximately l/16 inch thick laminated to an
inner plastic film 12 of polyethylene approximately 2 mils thick,
the two members lO and 12 being coextensive in area and bonded
together throughout their extent to serve as a laminated insulat- ~
ing layer. A sealed rectangular flexible envelope 14 formed of -
two sheets of 2 mil polyethylene film 16, 18 folded together is ;~
secured to film 12 and foam plastic layer lO by heat sealing in
zones 20, 22 and 24 along three margins of the rectangular enve-
lope 50 that the face of the envelope 14 is adjacent the face of :~
the insulating layer. Disposed within envelope 14 is a second ~ ~ -
sealed envelope 26 formed of a single layer of 2 mil polyethylene
film or made up of composite layers of materials (inner layer
of polyethylene laminated to a slitted polyester film, sold under
the trademark Myler, and outer layer of like Mylar film coated
with Saran polyvinylidene chloride) and filled with a supply
28 of water. The water-containing envelope 26, because of
its relatively thin walls, is readily broken or ruptured by
pressuxe applied externally of outer envelope 14 without
breaking the walls of the outer envelope. Also disposed
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within outer envelope 14 is a supply 30 of dry solid ammonium
nitrate in finely divided form. Preferably, air is evacuated
from outer envelope 14 before heat sealing is completed so that
the walls of the two envelopes will abut each other to facili-
tate rupturing of the inner envelope by external pressure.
Envelope 14 e~tends over only a portion of the length of members
10 and 12 so that the latter extends beyond the heat sealed mar-
gin of envelope 14 to form a flap 32. To the margin of flap 32
remote from envelope 14 is secured as a closure member one or ~
more lengths of pressure sensitive adhesive tape 34 provided with -;
a removable temporary protective cover sheet 36 over its exposed
aclhesive face. Alternatively, a rubber band or piece of string, -
a band of cohesive (self-adherent) material or other mechanical
fastening may be used in place of adhesive tape 34.
Although envelope 14 and insulation layer 10 are rec-
tangular in configuration in the embodiment described above, it
will be appreciated that other shapes such as oval may also be
used. Indeed, it is possible, although less convenient, to have
the insulation layer unattached to the outer en~elope 14 but
instead in the form of a separate flexible sheet together with a
closure mèmber; if desired, the separate insulation layer may be
preformed into a cylindrical chamber or a box of appropriate
dimensions. ~-
In order to achieve the desired results, it is essen-
tial that the ratio vf ammonium nitrate to water be from 1.24~
to 1.26:1 by weight. In the case of a blood sample which is 5 ;
cc. by volume, the size sample which is usually employed, the
weight of ammonium nitrate and water should be from 180 to 200
grams for best results.
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In using the cold pack, the barrel of the syringe into
which the blood sample is drawn in the usual manner is sealed by
inserting the end of the needle into a rubber stopper, or else
the needle is first disconnected and discarded, after which the
barrel is sealed. Inner envelope 26 is ruptured by manipulation
of the cold pack so that the water is mixed with the ammonium
nitrate, and barrel 38 of the syringe filled with the blood sam-
ple is then placed in the position indicated by printed design
40 on the face of envelope 14, and the envelope, together with
the outer insulating layer, is folded upon itself to envelop the
syringe barrel as shown in Figs. 3 and 4. Temporary protective
sheet 36 is stripped from the adhesive tape and the latter is
pressed against the exposed face of insulation layer 10 as shown
in Figs. 3 and 4 to maintain the cold pack releasably in folded
position snugly enveloping the syringe barrel 38. In the case
where the insulatlng layer is separate from the envelope 14, it
may be wrapped around the envelope simultaneously with envelop- ~-
ment of the syringe barrel 38 by the envelope or subsequently
~hereto, and secured in place by a closure member. In the case
where the separate insulating layer is preformed into a container
or box, the insulating layer can be rigid or stiff instead of
flexible if desired and the container or box is of such size
that the rolled-up envelope 14 enclosing syringe barrel 38 is a
snug fit within lt, so that after insertion the envelope is main-
tained in rolled-up condition around the syringe barrel.
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