U.S. patent number RE38,695 [Application Number 09/948,276] was granted by the patent office on 2005-02-08 for extravasation detection electrode patch.
This patent grant is currently assigned to E-Z-EM, Inc.. Invention is credited to Jack Goodman, Arthur Zimmet.
United States Patent |
RE38,695 |
Goodman , et al. |
February 8, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Extravasation detection electrode patch
Abstract
A medical extravasation device has an electrode patch that can
attach to the skin for sensing electrical information. Tissue
impedance is calculated from the electrode patch signals. The patch
has elongate pick-up electrodes inboard of elongate energizing
electrodes. The measuring zone determined by the elongate space
between the pick-up electrodes enhances sensitivity and
specificity. The presence of an extravasation is determined by
interpreting the tissue impedance measurement. The method for
determining the extravasation includes a first step of determining
a pre-injection baseline measurement of the tissue impedance. Then,
the tissue impedance is monitored during the procedure itself. A
predetermined amount of change in tissue impedance is determined to
indicate an extravasation.
Inventors: |
Goodman; Jack (Ann Arbor,
MI), Zimmet; Arthur (Centerport, NY) |
Assignee: |
E-Z-EM, Inc. (Lake Success,
NY)
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Family
ID: |
27539064 |
Appl.
No.: |
09/948,276 |
Filed: |
September 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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924631 |
Sep 5, 1997 |
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491149 |
Jun 16, 1995 |
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323595 |
Oct 17, 1994 |
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182221 |
Jan 14, 1994 |
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Reissue of: |
957121 |
Oct 24, 1997 |
05964703 |
Oct 12, 1999 |
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Current U.S.
Class: |
600/382; 600/384;
600/393; 600/396; 600/547 |
Current CPC
Class: |
A61M
5/16836 (20130101); A61B 5/0535 (20130101) |
Current International
Class: |
A61B
5/053 (20060101); A61M 5/168 (20060101); A61B
005/04 () |
Field of
Search: |
;600/382,372,384,386,393,396,506,547 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0784960 |
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Jul 1997 |
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EP |
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757151 |
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Sep 1980 |
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SU |
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WO 99/29356 |
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Jun 1999 |
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WO |
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Other References
Contrast Media--Early Detection of Extravasation of Radiographic
Contrast Medium James Shaeffer, PhD, Sture V. Sigfred, MD, Matthew
A. Sevcik, MD, Richard S. Grabowy, MS, Lee Ann Gemmell, BSEE, Alan
D. Hirschman, PhD; Jul. 1992. .
Cancer letters--Detection of Extravasation of Antineoplastic Drugs
by Microwave Radiometry James Shaeffer, Anas M. El-mahdi, Albert E.
Hamwey Jr., and Kenneth L. Carr; Apr. 1, 1986. .
MMIC Receiver for Water-Vapor Radiometer NASA Tech Briefs, Sep.
1993. .
Recent Development in Modeling Heat Transfer in Blood Perfused
Tissues H. Arkin, L. Xi Xu and K. R. Holmes IEEE Transactions on
Biopmedical Enginnering vol. 41 No. 2 Feb. 1994. .
Infusion Line Model for the Detection of Infiltration Extravasation
and other Fluid Flow Faults Thomas S. Harris and Wolf W. von
Maltzahn, Senior Member IEEE IEEE Transaction on Biomedical
Engineering vol. 40 No. 2 Feb. 1993. .
Multiangle Method for Temperature Measurement of Biological Tissues
by Microwave Radiometry Jean Montreuil and Manfred Nachman
Transactions on Microwave Theory and Techniques vol. 39 No. 7 Jul.
1991. .
Use of Gallium Arsenide in Medical Applications by Ken Car
.COPYRGT. 1995..
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Primary Examiner: Smith; Ruth S.
Attorney, Agent or Firm: Alston & Bird LLP
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No.
08/924,631 filed Sep. 5, 1997 now abandoned, which is a
continuation of application Ser. No. 08/491,149 filed on Jun. 16,
1995 now abandoned which in turn is a continuation of Ser. No.
08/323,595 filed on Oct. 17, 1994 now abandoned which is in turn a
continuation of Ser. No. 08/182,221 filed on Jan. 14, 1994 now
abandoned; all of which were titled Extravasation Detection System.
Claims
What is claimed is:
1. An electrode patch for use in a non-invasive device for
detecting extravasation that may occur when a needle with a tip is
inserted into a patient in order to introduce fluid into the
vascular system of a patient, comprising: a body of the patch
adapted to be affixed to the skin of a patient, an outer pair of
elongated electrodes and an inner pair of elongate electrodes, the
length of each of said electrodes being deployed along the body of
said patch, said inner pair of electrodes being spaced from one
another on either side of a center line, said inner pair defining a
measuring zone, said measuring zone being shaped and dimensioned to
encompass a needle tip within said zone, said zone being small
enough to optimize sensitivity, said inner pair being long enough
to facilitate placement of the patch over a needle tip inserted
into a patient, each of said outer pair of electrodes being
outward, relative to said center line, of a respective one of said
inner electrodes, energization of said outer electrodes, when said
patch is affixed to the skin of a patient, providing a field which
induces a signal in said inner electrodes that is a function of the
impedance of the tissue in said measuring zone.
2. The patch of claim 1 wherein each of said electrodes further
includes a first portion which is relatively short as compared to
said elongate portion of each electrode, said relatively short
first portions of said electrodes define a coupling region which
can be connected to a single clip containing electrical
contacts.
3. The patch of claim 1 wherein each of said elongate electrodes
are substantially the same length and wherein each of said outer
pair of electrodes is adjacent to and spaced from one of said inner
pair of electrodes.
4. The patch of claim 3 wherein each of said elongate electrodes
has a total length of about 3 inches, and a width of about 3/16th
of an inch, and wherein said inner pair of electrodes is spaced
apart by about 0.75 inches and said outer pair of electrodes is
spaced apart by about 1.5 inches, and where said inner pair of
electrodes is centralized relative to said outer pair of
electrodes.
5. The patch of claim 4 wherein said body is about two inches in
width and about three inches in length.
6. The patch of claim 1 wherein said electrodes are silver/silver
chloride strips..Iadd.
7. A device for use with a non-invasive detection system to detect
extravasation when fluid is delivered into a patient's vascular
system, comprising: a) an outer pair of elongated electrodes and an
inner pair of elongated electrodes, b) said inner pair of
electrodes being spaced from one another on either side of a center
line, said inner pair defining a measuring zone, said measuring
zone being shaped and dimensioned to encompass within said zone an
end of a channel inserted in the patient's vascular system for
delivering fluid into the vascular system, said zone being small
enough to optimize sensitivity, said inner pair being long enough
to facilitate placement of the end of the channel within the
measuring zone; c) each of said outer pair of electrodes being
outward, relative to said center line, of a respective one of said
inner electrodes, d) energization of said outer electrodes
providing a field which induces a signal in said inner electrodes
that is a function of the impedance of the tissue in said measuring
zone..Iaddend..Iadd.
8. A device for use with a non-invasive detection system to detect
extravasation when fluid is delivered into a patient's vascular
system, comprising: a) an outer pair of elongated electrodes and an
inner pair of elongated electrodes, b) said inner pair of
electrodes being spaced from one another on either side of a center
line, said inner pair defining a measuring zone, said measuring
zone being shaped and dimensioned to encompass within said zone an
end of a channel inserted in the patient's vascular system for
delivering fluid into the vascular system, said zone being sized to
detect extravasation in the measuring zone and long enough to
facilitate placement of the end of the channel within the measuring
zone; c) each of said outer pair of electrodes being outward,
relative to said center line, of a respective one of said inner
electrodes, d) energization of said outer electrodes providing a
field which induces a signal in said inner electrodes that is a
function of the impedance of the tissue in said measuring
zone..Iaddend..Iadd.
9. A device for use with a non-invasive detection system to detect
extravasation when fluid is delivered into a patient's vascular
system; said device comprising: a) first and second electrodes; the
electrodes being separated from each other to encompass the end of
a channel inserted in the patient's vascular system for delivering
fluid into the vascular system; b) the first and second electrodes
defining a measuring zone; the measuring zone being sized to detect
extravasation in the measuring zone; and c) third and fourth
electrodes to provide an electrical field which induces a voltage
signal between the first and second electrodes; said signal being a
function of the impedance of the tissue in the measuring
zone..Iaddend..Iadd.
10. The device of claims, 7, 8 or 9, wherein the electrodes are
substantially the same length..Iaddend..Iadd.
11. The device of claim 10 wherein each electrode is about 3 inches
in length, and about 3/16.sup.th of an inch
wide..Iaddend..Iadd.
12. The device of claims 7, 8, or 9, wherein the electrodes are
silver/silver chloride strips..Iaddend..Iadd.
13. The device of claims 7, 8, or 9, wherein each of the electrodes
has a hydrogel material thereon..Iaddend..Iadd.
14. The device of claims 7, 8, or 9, wherein the electrodes are
substantially parallel relative to each other..Iaddend..Iadd.
15. The device of claims 7, 8, or 9, wherein each of the electrodes
includes a coupling region capable of being connected to a clip
having electrical contacts..Iaddend..Iadd.
16. The device of claim 8, wherein the length of the outer pair of
elongated electrodes and the inner pair of elongated electrodes are
deployed along a base; said base adapted to be affixed to the
patient's skin..Iaddend..Iadd.
17. The device of claim 9, wherein the first and second electrodes
are positioned between the third and fourth
electrodes..Iaddend..Iadd.
18. The device of claim 17, wherein the third and fourth electrodes
are substantially parallel relative to each
other..Iaddend..Iadd.
19. The device of claim 9, wherein the length of the first and
second electrodes and the third and fourth electrodes are deployed
along a base; said base adapted to be affixed to the patient's
skin..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to a device and method for the detection of
extravasation and more particularly to the detection of
extravasation of ionic and non-ionic contrast media.
Extravasation or infiltration is a complication related to the use
of power injectors during contrast media injection procedures. When
an extravasation occurs, contrast is injected into the tissue
surrounding the blood vessel, instead of into the blood vessel
itself. The causes for extravasation vary, ranging from operator
error in placement of the needle to physiological limitations of
the blood vessel to tolerate the rate of fluid administration.
Complications related to extravasation may be quite severe and may
include tissue necrosis. This may require reconstructive surgery to
repair.
Presently, the only method for detecting an extravasation is for
the operator to visually observer it. However, by the time an
extravasation is visually observable, much of the previously
discussed damage may have occurred.
Accordingly, it is an object of the present invention to provide a
safe, efficient, inexpensive and reliable means for the early
detection of extravasations.
A very large number of contrast media injection procedures are
undertaken each year in the United States; something in the order
of ten million. Less than 0.2% of these procedures result in an
extravasation. Yet the absolute number is substantial because the
base number is so large. The occurrence of an extravasation
requires that the procedure be terminated and reinstituted.
Accordingly, in a normal situation where an extravasation occurs,
early detection is important from the point of view of minimizing
the impact on the patient, saving time and providing a timely
reinstitution of the procedure.
Although extravasation is not life-threatening, when it does occur
it causes discomfort to the patient. It requires a great deal of
attention from the doctor and usually means that a procedure has to
be interrupted. Thus, it is important that any extravasation
detection technique avoid a false indication of extravasation.
In relatively rare cases the extravasation can be quite harmful to
the patient. Therefore early detection will avoid patient trauma or
other injury.
The false detection of an extravasation results in terminating a
procedure. Starting the procedure constitutes unnecessary trauma to
the patient and expense. Therefore, any detection technique that
gives a noticeable number of false indications will not be used by
the doctor.
Accordingly, it is important that any detection technique to be
acceptable combine an extremely small number of false indications
of extravasation coupled with a reasonably high specificity to the
extravasation event being detected.
The relatively large number of contrast media injections undertaken
coupled with the relatively small percentage of extravasations that
occur means that any procedure to be acceptable to the medical
profession has to be non-invasive.
It is an accepted fact that any invasive procedure carries with it
risks and trauma. They are to be avoided unless the benefit
trade-off warrants such.
Thus, in order for an extravasation detection technique to be
acceptable in this context, it must meet the following
objectives.
First, it has to be inexpensive and be a disposable single use
item.
Second, it must be relatively acceptable to the patient. Therefore,
it should be non-invasive and create no pain or other patient
problem.
Third, it has to be easy for the technician or doctor to use and
readily fits within the procedure involved in the contrast media
injection routine.
Fourth, and perhaps more importantly, it must provide next to no
false indications of extravasation. A false indication would mean
stopping a procedure which did not have to be stopped. Thus it
follows that the technique must be specific to extravasation and
non-responsive to other phenomenon such as the patient moving his
or her arm.
Only a device that meets the above criteria (a) will be safe, (b)
have technicians and doctors willing to use it, (c) have patients
accept it and (d) have it come within the economic requirements of
the institution providing the media injection procedure.
BRIEF DESCRIPTION
The present invention relates to an extravasation detection device
and a method for the detection of extravasations. The extravasation
device is an electrode patch for sensing certain electrical
information.
The electrode patch has a body portion which is adapted to be
removably affixed to the skin of a patient. Outer and inner pairs
of elongated electrodes are deployed along the body of the patch.
The inner pair defines a measuring zone which is shaped and
dimensioned to encompass the tip of the needle within the zone. The
zone is small enough to optimize sensitivity yet large enough to
facilitate placement of the patch over the needle tip. When the
body of the patch is affixed to the skin of the patient and
alternating electrical energy is applied to the outer electrodes, a
field is provided which induces a signal in the inner electrodes,
which field is a function of the impedance of the tissue of the
measuring zone.
Information from the electrode patch is gathered and processed in
order to calculate tissue impedance. The presence of an
extravasation is determined by interpreting the tissue impedance
measurement and, in that way, extravasations can be detected early.
The method for determining the extravasation includes a first step
of determining a pre-injection baseline measurement of the tissue
impedance.
The electrode patch is affixed so that the measuring zone
encompasses the tip of the needle. Energizing the outer pair of
electrodes induces a signal in the inner pair of electrodes as a
function of the impedance of the body tissue in the measuring zone.
Tissue impedance is measured during the media injection procedure
using the electrical information sensed by the inner pair of
electrodes. The characteristics of the change in this impedance
from the baseline impedance measurement is determined. This tissue
impedance is monitored during the injection procedure. A
predetermined characteristic of the change in tissue impedance
indicates extravasation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall perspective view with parts separated of the
underside of the preferred embodiments, illustrating the backing
paper peeling off the adhesive-backed body of the electrode patch
with an open spring clip connector adjacent.
FIG. 2 is a top plan view of the electrode-patch, illustrating the
conductive electrode strips within the patch.
FIG. 3 is a perspective view of the lower jaw of the spring clip
connector with a typical contact and hardware exploded off.
FIG. 4 is a perspective view of a typical method of application,
with patch and clip shown prior to placement over the point of
needle insertion.
FIG. 5 is a diagrammatic plan view of a typical application and
apparatus hook-up.
FIG. 6 is a diagrammatic plan view of the patch in place on a
patient showing, in idealized form, the relation between an
extravasation and the measuring zone.
FIG. 7 is a bottom plan view of a presently preferred embodiment of
the patch similar to that shown in FIG. 2 except that the clear
release liner or ply 68 that is the base or bottom ply is omitted
from FIG. 7.
FIG. 8 is an exploded view of the FIG. 7 patch showing the plies
and elements which constitute the patch.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, the reference numeral 10 generally
denotes the extravasation detection system of the present
invention.
Extravasation detection system 10 includes an electrode patch 12
capable of sensing certain electrical information. Electrode patch
12, as best shown in FIG. 1, includes a PVC body 15 and an adhesive
backing 17. Adhesive backing 17 is protected by a clear release
backing sheet 19. Electrode patch 12 is formed with four spaced
apart electrodes thereon, two inner surface electrodes 18, 20 and
two outer surface electrodes, 22 and 24. Between inner electrodes
18, 20 a space 26 is provided. Space 26 is shaped and dimensioned
to permit a needle 21 to be placed thereunder and to optimize the
sensitivity of the system for the depth of the needle tip within
the tissue during a typical injection. By using adhesive backing
15, electrode patch 12 can be easily applied to, and removed from
the skin.
Electrode patch 12 is provided with a coupling region 23 shaped and
dimensioned to fit within a clip 28. Clip 28 is provided with
electrical contacts 30, 32, 34, 36 positioned within the clip so
that they can contact surface electrodes 18, 20, 22, 24 when
conductor-patch 12 is placed within clip 28. In a preferred
embodiment clip 28 includes a spring 25. Clip 28 has electrical
leads 50, 52 which connect to a constant alternating current source
of power and electrical leads 54, 56 which connects to voltage
potential measuring circuitry. Clip 28 further includes a first
conduit 27 hosing leads 50, 52, 54, 56 which connects to a device
29 which interprets the data sensed by electrode patch 12 and a
second conduit 40 which connects to a CT injector 42. Conduit 40
has capability to halt operation of injector 42 in the event an
extravasation has been detected or to convey this information to
injector 42.
In one embodiment, electrodes 18, 20, 22, 24 are silver/silver
chloride strips. Each of the electrodes has a first relatively
short vertical section 18a, 20a, 22a, 24a and a second relatively
long vertical section 18b, 20b, 22b, 24b. Each electrode has a
total length of about 3 inches and a width of about 3/16 of an
inch. Inner electrodes 18, 20 are spaced from one another by about
0.75 inches, and outer electrodes 22, 24 are spaced apart by about
1.5 inches.
In that embodiment, the electrode patch 12 has a length of about 3
inches and a width, at its widest point, of about 2 inches.
In use, the extravasation detective system of the present invention
works as follows. A syringe needle 21 is introduced into the
patient's vasculature. The release backing 19 is removed from the
patch body 15 and the electrode patch 12 is then adhered to the
patient's skin using adhesive backing 17. As heretofore mentioned,
patch 12 is portioned such that the needle tip is covered by the
space 26. Electrode patch 12 is clipped into clip 28 via coupling
region 23 so that surface electrodes 18, 20, 22, 24 are in contact
with electrical contacts 30, 32, 34, 36. Clip 28 is then connected
through conduit 27 to impedance monitoring and interpreting
circuitry in device 29. The provision of the short vertical
sections allows use of one clip for all electrical connections
without compromising the spacing of the surface electrodes in the
measurement area 26 of the electrode patch 12 where measurements
are being made.
Preliminary data is collected to determine the tissue impedance
before any injection is made. An injection is then started using
injector 42. Continuous calculations of tissue impedance are made
during the injection procedure. An extravasation is deemed to have
occurred if during the injection procedure the impedance change
shows a fairly consistent slope of at least plus or minus 0.5 ohms
per second when material is being infused into the vasculature at a
rate of more than 0.25 milliliters per second. It is contemplated
that, in certain embodiments of the invention, if it is determined
that such an extravasation has occurred, there will be an automatic
stop mechanism to cease the injection of the media, via conduit 40
or in the alternative some visual or other type of warning signal.
Ionic contrast media has a lower impedance than tissue and will
cause a decrease in tissue impedance during an extravasation.
Non-ionic contrast media has a higher impedance than tissue and
will cause an increase in tissue impedance during an
extravasation.
In order to have the appropriate data derived from the electrode
patch 12 a constant alternating current is applied to the two outer
electrodes 22, 24. The current and frequency used is about 200
micro amperes sinusoidal at 20 kilohertz. Inner electrodes 18, 20
provide measurement of voltage potential.
Device 10 provides a method of detecting extravasations. The method
includes the steps of determining a pre-injection of baseline
measurement for tissue impedance. It also involves the step of
determining the amount of change in tissue impedance which
indicates an extravasation.
Further, the method involves the step of monitoring tissue
impedance during an injection procedure to ascertain if the amount
of change previously determined indicates an extravasation has
occurred.
The aforementioned method, and system 10, has been used in
conjunction with injections of both ionic and non-ionic contrast
media to determine the existence of extravasation.
The slope change which is indicative of an extravasation was
derived from a series of tests done on animals. Animals were
intravenously injected, with both ionic and non-ionic contrast
media. Prior to each injection, a measurement of tissue impedance
was made and during the course of the injections continuous
measurements of tissue impedance were made. It was found that when
the injections were intravenous (no extravasation) there was very
little change in kin impedance over time. A second series of ionic
and non-ionic contrast media were also made.
These injections were deliberately made out of the vasculature to
simulate an extravasation. During these injections, a substantial
change in tissue impedance occurred almost instantaneously. These
impedance was plotted as a function of time to determine the slope
change indicative of an extravasation.
Set forth below in Table 1 is a summary of four studies done on
doges in the aforementioned manner. Tables 2-5 are the underlying
studies summarized in Table 1.
TABLE 1 Summary of Data From Five Dogs I.V. Infusion Extravasation
I.V. Infusion Extravasation Non-Toxic Non-Ionic Variable Ionic
Media Ionic Media Media Media Resting 36 Ohms 35.2 Ohms 29.4 Ohms
32.6 Ohms Impedance Slope 9.1% per -163% per 20.0% per 172% per
minute minute minute minute
TABLE 2 Results of Intravenous Injection of Ionic Contrast in 5
Dogs Mean Dog 1 Dog 2 Dog 3 Dog 4 Dog 5 (S.D.) Leg L R R L R
Baseline 30 47 29 36 38 36.0 Resistance Ohms Ohms Ohms Ohms Ohms
(7.2) Injected 20 cc 10 cc 10 cc 15 cc 50 cc 21.0 cc Volume (16.7
cc) % .DELTA.Z/ml 0.05 0.30 0.16 0.13 0.08 0.14 (0.10)
.DELTA.Ohms/ml 0.015 0.14 0.05 0.05 0.03 0.06 (0.05) % .DELTA.Z/min
5.4 18.0 10.0 7.5 4.6 9.1 (5.4)
TABLE 3 Results of Extravasation of Ionic Contrast in 5 Dogs Mean
Dog 1 Dog 2 Dog 3 Dog 4 Dog 5 (S.D.) Leg L R R L R Baseline 30 47
30 37 32 35.2 Resistance Ohms Ohms Ohms Ohms Ohms (7.2) Injected 10
cc 6 cc 3 cc 6 cc 5 cc 6.0 cc Volume (2.5 cc) % .DELTA.Z/ml -2.3
-4.0 -1.3 -2.0 -4.0 -2.7 (1.2) .DELTA.Ohms/ml -0.69 -1.9 -0.38
-0.74 -1.28 -1.0 (0.6) % .DELTA.Z/min -140.0 -240.0 -75.0 -120.0
-240.0 -163.0 (74)
TABLE 4 Results of Intravenous Injection of Non-Ionic Contrast in 5
Dogs Mean Dog 1 Dog 2 Dog 3 Dog 4 Dog 5 (S.D.) Leg R L L R L
Baseline 30 24 27 35 31 29.4 Resistance Ohms Ohms Ohms Ohms Ohms
(4.2) Injected 10 cc 10 cc 6 cc 4 cc 10 cc 8.0 cc Volume (2.8 cc) %
.DELTA.Z/ml 0.30 0.43 0.32 0.11 0.50 0.33 (0.15) .DELTA.Ohms/ml
0.09 0.10 0.09 0.04 0.16 0.10 (0.4) % .DELTA.Z/min 18.0 26.0 19.2
6.7 30.0 20.0 (8.9)
TABLE 5 Results of Extravasation of Non-Ionic Contrast in 5 Dogs
Mean Dog 1 Dog 2 Dog 3 Dog 4 Dog 5 (S.D.) Leg R L L R L Baseline 30
24 28 32 49 32.6 Resistance Ohms Ohms Ohms Ohms Ohms (9.6) Injected
5 cc 5 cc 3 cc 4 cc 3 cc 4.0 cc Volume (1.0 cc) % .DELTA.Z/ml 1.4
3.0 4.0 1.9 4.1 2.9 (1.2) .DELTA.Ohms/ml 0.41 0.72 1.12 0.60 2.0
1.0 (0.6) % .DELTA.Z/min 81.6 180.0 240.0 112.5 246.0 172.0
(74.0)
Device 10 and the method associated therewith, although thus far
only used to determine extravasations of ionic and non-ionic
control media, may be useful to determine extravasations of other
types of injectable fluids.
One value of the invention is that it involves a non-invasive
procedure. Another important consideration is that the electrode
configuration adequately encompasses and responds to the
extravasation.
During a procedure when the needle is in place within a vein, one
cannot visualize exactly where the needle tip is. Since the
extravasation occurs at the needle tip, one cannot be certain of
where that extravasation will precisely occur along the path of the
blood vessel. This invention with its elongated measuring zone 26
(between the pickup electrodes 18 and 20 of FIG. 2) provides the
required sensing area.
Furthermore, it is important that these sensing electrodes 18 and
20 have the opening 26 between them that is shown in FIG. 2 so that
the zone under that space 26 that is within the patient's body will
be sensed if an extravasation occurs.
These elongated sensing electrodes 18, 20 and parallel elongated
energizing current electrodes 22, 24 provide the configuration
necessary to reliably pickup an extravasation where it occurs. This
is illustrated in FIG. 6. Specifically, this sensitivity occurs
because applicant's structure assures placement of the electrodes
18, 20, 22, 24 around the point where the needle 21 enters the
skin. Thus, the extravasation 44 is substantially centered in the
measurement zone that is subtended by the inner electrodes 18, 20.
In general, the extravasation will be picked up within ten to
twenty ccs of extravasation.
It is the geometric configuration set forth in the above referenced
application which meets the objective of providing substantial
assurance that an extravasation will be detected yet nearly
completely avoid providing a false indication of extravasation.
FIGS. 7 and 8 illustrate a presently preferred embodiment of the
patch. As best seen in the exploded view of FIG. 8, the top of the
patch is a clear vinyl ply 60. This ply 60, has on the surface
facing the patient, an adhesive which serves to hold the electrodes
and to adhere the patch to the patient. Under this vinyl ply 60,
there is a reinforcement ply 62 that provides rigidity for the end
of the patch that is to be held by the clamp 28 (see FIG. 1). Just
below the reinforcement 62, and in large part in contact with and
held by the adhesive side of the ply 60 is the set of four
electrodes 64. A discussed in connection with FIG. 2, each
electrode has an elongate portion. These elongate portions are the
active portions for providing the field and for picking up the
signal. These electrodes 64 are essentially similar to the
electrode arrangement shown in FIG. 1. The patient side of each
electrode has a hydrogel coating to assure good contact against the
patient's skin. Since this hydrogel is conducting, it is important
that the hydrogel coating only be on the electrode and not on any
of the surfaces between the electrode since such would tend to
short out the signals involved. A clear insulating tape 66 along
the short portions of the electrodes has the important function of
minimizing interaction between the short portion of the electrodes
and the patient so that it is the long portion of the electrodes 64
which are the effective energization and pick up electrodes.
Finally, there is the clear release liner 68 having a perforated
line 70 that provides the base liner of the patch. As shown in FIG.
1, the release liner (which is the liner 19 in FIG. 1) can be bent
back initially so that the patch can be placed into the clamp 28
before it is put into use. Then when it is put into use, the main
portion of the liner 68 can be removed by ripping it at the
perforation line 70 so that the electrodes 64 can be placed against
the patient's skin. The patient side of the vinyl layer 60 has the
pressure sensitive adhesive that will adhere the patch firmly to
the patient's skin.
FIG. 7 shows the assembly of the FIG. 8 plies with the clear vinyl
ply omitted. The overall dimensions are about 3.7 inches by 2.3
inches. The electrodes 64 are each about 0.2 inches wide and the
elongate portions are about two inches. The hydrogel coating in the
electrodes 64 ends at the line 72. The spacing between the inboard
edges of the inner electrodes is about 0.70 inches and the spacing
between the inboard edges of the outer pair of electrodes is about
1.5 inches.
* * * * *