U.S. patent application number 09/756173 was filed with the patent office on 2001-05-10 for process and devices for determining the instant of injection and the duration of injection in thermodilution measurements.
Invention is credited to Joeken, Stephan, Pfeiffer, Ulrich, Seebauer, Tobias.
Application Number | 20010001115 09/756173 |
Document ID | / |
Family ID | 7841361 |
Filed Date | 2001-05-10 |
United States Patent
Application |
20010001115 |
Kind Code |
A1 |
Pfeiffer, Ulrich ; et
al. |
May 10, 2001 |
Process and devices for determining the instant of injection and
the duration of injection in thermodilution measurements
Abstract
The present invention relates to a process and devices for
determining the instant of injection and the duration of injection
in thermodilution measurements in which an injectate fluid at a
temperature deviating from the temperature of the blood of a
patient is injected at a specific injection site into a blood
vessel of the patient and the temperature of the blood is measured
at a measuring site downstream of the injection site, the injectate
fluid being used at approximately room temperature and, before
entry into the blood vessel, passed via a temperature sensor which,
before the measurement, has a temperature deviating from room
temperature, the temperature determined by the temperature sensor
being sensed continuously, the instant of the beginning of
injection being determined from a change occurring in the sensed
temperature and the instant of the end of injection being
determined from a subsequently occurring change in direction of the
temperature profile.
Inventors: |
Pfeiffer, Ulrich; (Munchen,
DE) ; Joeken, Stephan; (Munchen, DE) ;
Seebauer, Tobias; (Munchen, DE) |
Correspondence
Address: |
NIXON PEABODY LLP
8180 GREENSBORO DRIVE
SUITE 800
McLean
VA
22102
US
|
Family ID: |
7841361 |
Appl. No.: |
09/756173 |
Filed: |
January 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09756173 |
Jan 9, 2001 |
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09144276 |
Aug 31, 1998 |
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6200301 |
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Current U.S.
Class: |
604/118 |
Current CPC
Class: |
A61B 5/028 20130101 |
Class at
Publication: |
604/118 |
International
Class: |
A61M 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 1997 |
DE |
197 38 942.2 |
Claims
What is claimed is:
1. A central vein catheter for the injection of an injectate fluid
having a temperature deviating from the temperature of the blood of
a patient into the central vein of the patient or carrying out
thermodilution measurements in which the temperature of the blood
is measured at a measuring side downstream of the central vein by a
separate device, the catheter comprising: an elongate catheter
body, having at least one injection lumen, with a distal end and a
proximal end; at least one connection device at the proximal end
for connecting at lest one injectate source to the injection lumen
for introducing the injectate fluid; at least one port of the
injection lumen in the vicinity of the distal end of the catheter
body for introducing the injectate fluid into the central vein of
the patient; at least one temperature sensor, which is arranged
inside the catheter body proximally with respect to the port of the
injection lumen; and at least one evaluation circuit, connected to
the temperature sensor for receiving and evaluating the temperature
profile determined by the temperature sensor for determining the
instant of injection and the duration of injection.
2. The catheter as claimed in claim 1, wherein the temperature
sensor is arranged laterally adjacent to the injection lumen.
3. The catheter as claimed in claim 1, wherein there is provided at
least one further lumen, which is designed as a sensor lumen and in
which the temperature sensor is arranged.
4. The catheter as claimed in claim 3, wherein the sensor lumen is
arranged centrally inside the catheter body.
5. The catheter as claimed in claim 3, wherein the sensor lumen
ends in the vicinity of the distal end of the catheter body.
6. The catheter as claimed in claim 1, further comprising a heat
conductive separating wall between the injection lumen and the
temperature sensor.
7. The catheter as claimed in claim 1, wherein at least one
clearance is provided between the injection lumen and the
temperature sensor.
8. The catheter as claimed in claim 1, wherein at least one further
lumen is provided inside the catheter body.
9. A device for determining the instant of injection and the
duration of injection in thermodilution measurements in which an
injectate fluid at a temperature deviating from the temperature of
the blood of a patient is injected at a specific injection side
into a blood vessel of the patient and the temperature of the blood
is measured at a measuring side downstream of the injection site,
which has: an extacorporeal sensor housing which has at least one
input connection, which can be connected to at least one injectate
source, and at least one output connection, which can be connected
to a blood vessel catheter; at least one temperature sensor which
is arranged in the sensor housing, continuously senses the
temperature in a region between the input connection and the output
connection and can be connected via at least one line to at least
one measuring computer; and at least one heat contact plate of
skin-compatible, heat-conducting material for fastening the sensor
housing on the skin of the patient.
10. The device as claimed in claim 9, wherein the sensor housing is
provided in its regions facing away from the skin of the patient at
least partially with a heat-insulating layer.
11. The device as claimed in claim 9, wherein the heat contact
plate is designed as an adhesive plate.
12. The device as claimed in claim 9, wherein the input connection
and the output connection of the sensor housing are designed as a
female Luer lock connection and as a male Luer lock connection,
respectively.
13. The device as claimed in claim 9, further comprising means for
heating or cooling the sensor housing.
Description
BACKGROUND OF THE INVENTION
1. 1. Field of the Invention
2. The present invention relates to a process and devices for
detecting the instant of injection and for determining the duration
of injection in hemodynamic monitoring by means of
thermodilution.
3. 2. Description of the Prior Art
4. The measurement of hemodynamic parameters, for example the
cardiac output, is largely performed at present either by means of
pulmonary arterial or transcardiopulmonary thermodilution (Pfeiffer
U. J., Knoll R. (1993): Process for Determining a Patient's
Circulatory Fill Status. U.S. Pat. No. 5,526,817) or else by means
of thermo-dye-dilution (Pfeiffer, U. J., Backus G., Blumel G.,
Eckart J., Muller P., Winkler P., Zeravik J., Zimmermann G. J.
(1990): A Fiberoptics-Based System for Integrated Monitoring of
Cardiac Output, Intrathoracic Blood Volume. Extravascular Lung
Water, O.sub.2 Saturation, and a-v Differences. Practical
Applications of Fiberoptics in Critical Care Monitoring, Springer
Verlag, 114-125). In these processes, a defined volume of an
indicator substance which is as cold as possible, for example
glucose or saline solution, is injected. The instant of injection
is registered by means of an extracorporeal temperature sensor
which is integrated directly in the injection lumen.
5. At the same time, the thermodilution measurement is started by
means of a thermosensor, which in the case of pulmonary arterial
measurement is located in the distal lumen of the pulmonary artery
catheter in the Arteria pulmonalis or, in the case of
transcardiopulmonary measurement, in the tip of a catheter lying in
the Arteria femoralis or in the Aorta abdominalis. By plotting the
thermodilution curve, the cardiac output can be calculated, for
example by means of the Stewart-Hamilton method.
6. The special aspect of the transcardiopulmonary method is the
additional determination of a number of cardiovascular parameters,
in particular for assessing the output status, for example by the
intrathoracic blood volume. For the calculation of these
parameters, knowledge of the characteristic times of the
indicators, in particular the mean transit time and exponential
fall time, is required. To be able to calculate these exactly, the
instant of injection, the mean passage time of the injectate and
the duration of injection must in turn be accurately measured,
which is accomplished by means of the curve plotted using the
extracorporeal temperature sensor (cf. FIG. 1, which reproduces the
injection curve profile with a known injectate temperature sensor
system; in contrast to this, FIG. 2 shows the injection curve
profile with a sensor system according to the invention set out
below).
7. As a function of the temperature difference between ambient air
and injectate, the value T.sub.inj, required for correct
measurements, is calculated using additionally determined
correction factors.
8. A major disadvantage of the existing technique is that injectate
of a temperature deviating from room temperature was required for
optimum measurements in order to determine exactly the instant of
injection and the duration of injection, since the volume in the
customary extracorporeal injectate temperature sensor housing is
essentially at room temperature. To be able to detect the instant
at which injection starts and to be able to calculate the duration
of injection from the temperature profile, a clear temperature
difference between the fluid at the sensor before injection and the
injectate is required.
9. For this reason, it must be ensured that the injection solution
is available in a well cooled state at any time. This means
additional work also for the nursing staff in intensive care units
and in operating rooms. In addition, measurements often do not
proceed absolutely smoothly, with the result that injectate taken
out of cooling too early may already have warmed up again by the
time it is used; the same problem arises if a number of
measurements are carried out at short intervals one after the
other.
10. The use of cooling sets, which can be installed at the
patient's bed, does offer the advantage of an injectate cooled for
a certain time directly at the patient, but again brings about
considerable disadvantages due to increased work, for example to
obtain fresh ice for the cooling box, and due to the costs
additionally incurred.
SUMMARY OF THE INVENTION
11. Proceeding from the abovementioned disadvantages and
shortcomings of the prior art, the present invention is based on
the object of providing a process for detecting the instant of
injection and for determining the duration of injection which
allows optimum hemodynamic measurements with injectate kept at room
temperature by means of the thermodilution technique, it being
intended that the process can be accomplished without more work and
without any particular additional costs.
12. This object is achieved by a process for determining the
instant of injection and the duration of injection in
thermodilution measurements in which an injectate fluid at a
temperature deviating from the temperature of the blood of a
patient is injected at a specific injection site into a blood
vessel of the patient and the temperature of the blood is measured
at a measuring site downstream of the injection site, the injectate
fluid being used at approximately room temperature and, before
entry into the blood vessel, passed via a temperature sensor which,
before the measurement, has a temperature deviating from room
temperature, the temperature determined by the temperature sensor
being sensed continuously, the instant of the beginning of
injection being determined from a change occurring the sensed
temperature and the instant of the end of injection being
determined from a subsequently occurring change in direction of the
temperature profile.
13. The dependent patent claims 2 to 7 relate to advantageous
embodiments of the process according to patent claim 1.
14. U.S. Pat. No. 4,901,734 discloses a so-called pulmonary artery
catheter ("Apparatus [ . . . ] by single pulmonary arterial
catheterization"; cf. lines 1 and 2 of the Abstract of U.S. Pat.
No. 4,901,734). Such a pulmonary artery catheter is advanced via
the Vena cava superior, the central vein, the right-hand atrium and
the right-hand ventricle into the Arteria pulmonalis. For this
reason, the pulmonary artery catheter has a proximal lateral
opening (cf. reference numeral 215 in FIG. 6 of U.S. Pat. No.
4,901,734), which with the positioning described above lies in the
central vein, while the distal sensor (cf. reference numeral 201 in
FIG. 6 of U.S. Pat. No. 4,901,734), provided in the region of the
tip, lies--as mentioned--in the Arteria pulmonalis.
15. The catheter device known from U.S. Pat. No. 4,901,734 is
formed with a number of lumens and has a distally arranged
thermistor, a proximally arranged thermistor and a plurality of
electrical sensor means connected to the thermistors. In this case,
the proximal thermistor is arranged such that it is essentially
immersed totally in the blood/injectate mixture in order to
determine its temperature immediately (cf. Abstract of U.S. Pat.
No. 4,901,734).
16. However, there is a considerable disadvantage to be seen in the
fact that the temperature sensor is provided in the form of the
proximal thermistor directly in the injection lumen, to the extent
that as a result the injectate flow must to a certain extent be
"diverted", that is to say must be directed around the temperature
sensor and, as it does so, mixes directly with the blood flowing
past the proximal lateral opening (cf. reference numeral 215 in
FIG. 6 of U.S. Pat. No. 4,901,734) due to turbulence. Owing to the
turbulence described, the exact determination of the temperature of
the injectate, and consequently also the precise determination of
the instant at which the injectate arrives, is not possible, in
particular if there is a comparatively small difference between the
temperature of the injectate and the temperature of the blood. In
addition, such a diversion of the injectate flow is not only
troublesome but, with certain catheter positions, may also hinder
and/or delay the introduction of the injectate.
17. Furthermore, in the case of the pulmonary artery catheter known
from U.S. Pat. No. 4,901,734, no possibility is provided for
determining the instant of injection and the duration of injection.
The sensing of the temperature of the blood/injectate mixture
serves in particular for determining the so-called "temperature
base line" (cf. column 4, lines 51 to 53 of U.S. Pat. No.
4,901,734).
18. The shortened response time aimed for according to U.S. Pat.
No. 4,901,734, of 0.5 to 0.75 seconds (cf. column 4, line 45 of
U.S. Pat. No. 4,901,734), has the effect that the temperature base
line is reached more quickly and its determination is more exact.
However, a time measurement is neither provided nor intended.
19. Proceeding from the abovementioned disadvantages and
shortcomings of the prior art according to U.S. Pat. No. 4,901,734,
the present invention is based on the object of providing a central
vein catheter for detecting the instant of injection and for
determining the duration of injection which allows optimum
hemodynamic measurements with injectate kept at room temperature by
means of the thermodilution technique, it being intended that the
catheter can be installed without more work and without particular
additional costs.
20. This object is achieved by a central vein catheter for the
injection of an injectate fluid having a temperature deviating from
the temperature of the blood of the patient into the central vein
of the patient for carrying out thermodilution measurements in
which the temperature of the blood is measured at a measuring site
downstream of the central vein by a separate device, which catheter
has:
21. an elongate catheter body, having at least one injection lumen,
with a distal end and with a proximal end;
22. at least one connection device at the proximal end for
connecting at least one injectate source to the injection lumen for
introducing the injectate fluid;
23. at least one port of the injectate lumen in the vicinity of the
distal end of the catheter body for introducing the injectate fluid
into the central vein of the patient;
24. at least one temperature sensor, which is arranged inside the
catheter body upstream of the port of the injection lumen for
continuously sensing the temperature of the injection lumen and the
connection lines of which are led to a connecting device at the
proximal end of the catheter body; and
25. at least one evaluation circuit, which can be connected to the
connecting device, for sensing and evaluating the temperature
profile determined by the temperature sensor for determining the
instant of injection and the duration of injection.
26. The catheter according to the present invention consequently
has at least one injection lumen for the application of
medicaments, for parenteral feeding, for removing blood or for
measuring the pressure in the central vein. At least one
temperature sensor is arranged inside the catheter body upstream of
the port of the injection lumen for continuously sensing the
temperature of the injection lumen and lies close to the injection
lumen, with the result that the temperature sensor, due to its
central position, is influenced only relatively little by external
factors, for example by disturbing injections through another
lumen. An intravasal determination of the injection temperature for
the thermodilution is made possible by the abovementioned
arrangement.
27. Since the intravasal dead space in the injection lumen of the
catheter is close to body temperature of 37 degrees Celsius, an
injectate kept at room temperature of about 20 degrees Celsius is
easily detected, because the temperature sensor has a temperature
deviating from room temperature during the measurement.
Consequently, the instant of injection and the duration of
injection can be determined exactly and, in combination with the
indicator dilution curves, the passage times of the indicators can
be calculated at the measuring sites in the Arteria
femoralis/Arteria radialis and also in the Arteria pulmonalis.
28. In contrast to the prior art according to U.S. Pat. No.
4,901,347, in the case of the central vein catheter according to
the invention the injectate flow does not have to be diverted, that
is to say it does not have to be directed around the temperature
sensor; rather, the temperature determination takes place by it
being possible for the injectate to be passed through the injection
lumen immediately and by a direct path past the temperature sensor,
the injectate is thus not being hindered or delayed in its flow.
Consequently, the temperature of the pure injectate and not--as in
the case of U.S. Pat. No. 4,901,734--the temperature of the
blood/injectate mixture is determined.
29. The dependent patent claims 9 to 16 relate to advantageous
embodiments of the catheter according to patent claim 8, attention
being drawn in particular to a preferred development, in which the
temperature sensor is arranged laterally adjacent to the injection
lumen, in order to make possible good thermal contact between the
injection lumen and the temperature sensor.
30. According to a further preferred development, there is provided
a further lumen, which is designed as a sensor lumen and in which
the temperature sensor is arranged. This further lumen, the
so-called sensor lumen, may lie in the direct proximity of the
injection lumen opening out at the tip of the catheter device and,
due to its central position, is influenced only relatively little
by external factors, for example by disturbing injections through
another lumen. In this sensor lumen there may be disposed the
temperature sensor which makes possible an intravascal
determination of the injection temperature for the
thermodilution.
31. U.S. Pat. No. 4,476,877 discloses a device for determining the
temperature of an injectate which has an extracorporeal,
small-volume sensor housing with a temperature sensor device which
is arranged inside the sensor housing and is connected via a line
to a measuring computer, the sensor housing being designed at the
ends such that it can be connected to the injection lumen of a
catheter and, at the opposite end, to an injection system.
32. However, a considerable disadvantage can be seen in the fact
that, in the case of the device known from U.S. Pat. No. 4,476,877,
no means are provided for arranging it directly on the skin of a
patient and in this way heating up the sensor housing to body
temperature of 37 degrees Celsius, to the extent that as a result
there is no possibility at all of using injectate kept at room
temperature in combination with the temperature sensor device.
Consequently, the device known from U.S. Pat. No. 4,476,877 cannot
have a temperature deviating significantly from the room
temperature of the injectate during the measurement, as a result of
which accuracy and reliability are not ensured in the determination
of the duration of injection and the instant of injection.
33. Proceeding from the abovementioned disadvantages and
shortcomings of the prior art according to U.S. Pat. No. 4,476,877,
the present invention is based on the object of providing a device
for detecting the instant of injection and for determining the
duration of injection which allows optimum hemodynamic measurements
with injectate kept at room temperature by means of the
thermodilution technique, it being intended that the device can be
installed without more work and without particular additional
costs.
34. This object is achieved by a device for determining the instant
of injection and the duration of injection in thermodilution
measurements in which an injectate fluid at a temperature deviating
from the temperature of the blood of a patient is injected at a
specific injection site into a blood vessel of the patient and the
temperature of the blood is measured at a measuring site downstream
of the injection site, which device has:
35. an extracorporeal sensor housing which has at least one input
connection, which can be connected to at least one injectate
source, and at least one output connection, which can be connected
to a blood vessel catheter;
36. at least one temperature sensor which is arranged in the sensor
housing, continuously senses the temperature in a region between
the input connection and the output connection and can be connected
via at least one line to at least one measuring computer; and
37. at least one heat contact plate of skin-compatible,
heat-conducting material for fastening on the skin of the
patient.
38. The device according to the present invention consequently has
an extracorporeal sensor housing and at least one temperature
sensor which is arranged in the sensor housing and protrudes into
the lumen of the sensor housing. The picked-off temperature signal
is passed on to the measuring computer via a line with a suitable
connector.
39. According to the invention, the device has at least one heat
contact plate of skin-compatible, heat-conducting material for
fastening on the skin of the patient. In this way, the injectate is
warmed up in the sensor housing by means of the body heat given off
by the patient, to be precise distinctly above room temperature,
depending on the skin temperature, the fastening site and the
spatial conditions (according to experience with normothermic
patients by distinctly more than 2 degrees Celsius).
40. Consequently, in spite of extracorporeal or extravasal
localization of the temperature sensor, there occurs a distinct
temperature difference between the injectate at room temperature
and the dead space, with the result that an exact and reliable
detection of the duration of injection and the instant of injection
is in any case ensured.
41. In contrast to the prior art according to U.S. Pat. No.
4,476,877, in the case of the device according to the present
invention there is consequently the possibility of using injectate
kept at room temperature in combination with the temperature
sensor. Consequently, the device according to the present invention
may have a temperature deviating from the room temperature of the
injectate during the measurement, as a result of which accuracy and
reliability are ensured in the determination of the duration of
injection and the instant of injection.
42. The dependent patent claims 18 to 23 relate to advantageous
embodiments of the device according to patent claim 17.
43. Further developments, features and advantages of the present
invention are explained in more detail below with reference to the
two exemplary embodiments illustrated by way of example in FIGS. 3
to 5.
BRIEF DESCRIPTION OF THE DRAWINGS
44. In the drawing:
45. FIG. 1 shows the injection curve profile with an injectate
temperature sensor system known from the prior art;
46. FIG. 2 shows the injection curve profile with a sensor system
according to the present invention;
47. FIG. 3a shows a diagrammatic longitudinal sectional view of a
central vein catheter according to the present invention;
48. FIG. 3b shows a diagrammatic cross-sectional view of the
central vein catheter from FIG. 3a;
49. FIG. 4 shows a diagrammatic longitudinal sectional view of a
device for determining the instant of injection and the duration of
injection in thermodilution measurements according to the present
invention; and
50. FIG. 5 shows a flowchart for determining the instant of
injection, the duration of injection and the temperature.
DETAILED DESCRIPTION
51. The devices illustrated by way of example in FIGS. 3 and 4 are
generally used in a process for determining the instant of
injection and the duration of injection in thermodilution
measurements in which an injectate fluid at a temperature deviating
from the temperature of the blood of a patient is injected at a
specific injection site into the blood vessel of the patient and
the temperature of the blood is measured at a measuring site
downstream of the injection site.
52. It can be regarded here as a notable special aspect that the
injectate fluid is used at approximately room temperature and,
before entry into the blood vessel, is passed via a temperature
sensor which, before the measurement, has a temperature deviating
significantly from room temperature, that is to say by at least two
degrees Celsius, the temperature determined by the temperature
sensor being continuously sensed, the instant of the beginning of
injection being determined from a change occurring in the
temperature sensed and the instant of the end of injection being
determined from a subsequently occurring change in direction of the
temperature profile.
53. The two exemplary embodiments explained in FIGS. 3 and 4 have
in common that the temperature sensor is brought to a temperature
deviating from room temperature by contact with the body of the
patient. Here, as described in detail below, the temperature sensor
in the case of the exemplary embodiment according to FIG. 3 is
brought to a temperature deviating from room temperature by blood
contact, whereas the temperature sensor in the case of the
exemplary embodiment according to FIG. 4 is brought to a
temperature deviating from room temperature by outer skin
contact.
54. FIG. 3a shows a diagrammatic longitudinal sectional view, FIG.
3b a diagrammatic cross-sectional view of a central vein catheter
according to the present invention.
55. The central vein catheter has a four-lumen catheter body 6,
which is ideally produced from not very thrombogenic material, such
as for instance polyurethane.
56. In addition to three conventional lumens 1, 4, 5, with
different diameters and ending at the catheter tip or proximally
with respect thereto, for the application of medicaments, for
parenteral feeding, for removing blood or for measuring the
pressure in the central vein, there is centrally in the catheter
body 6 a further lumen 2, which as a so-called sensor lumen 2 lies
in the direct proximity of the so-called injection lumen 1, opening
out at the catheter tip, and, due to its central position, is
influenced little by external factors, for example by disturbing
injections through one of the other lumens 4, 5.
57. The sensor lumen 2 ends blind before the catheter tip. In the
sensor lumen 2 there is disposed a temperature sensor 3, which at
the proximal end of the intravasal catheter portion goes over into
a channel extension with a temperature sensor connector (not
explicitly shown in FIGS. 3a and 3b). By means of this temperature
sensor 3, it is possible to determine intravasally the injection
temperature for the thermodilution.
58. The optimum temperature transfer from the injection lumen 1 to
the temperature sensor 3 takes place by means of a very thin
separating wall 7 with good heat-conducting properties and by means
of a clearance 8 between the injection lumen 1 and the sensor lumen
2.
59. Since the intravasal dead space in the injection lumen 1 of the
catheter is close to body temperature of 37 degrees Celsius, an
injection bolus kept at room temperature of about 20 degrees
Celsius is easily detected, which is not ensured in the case of the
conventional extracorporeal injectate temperature sensors. Thus,
the instant of injection and duration of injection can be
determined exactly and, in combination with the indicator dilution
curves, the passage times of the indicators can be calculated at
the measuring sites in the Arteria femoralis/Arteria radialis and
also in the Arteria pulmonalis.
60. With regard to application, it should be noted that the central
vein catheter represented in FIGS. 3a and 3b is placed in the
customary way by the Seldinger technique. For carrying out a
thermodilution, an artery and/or pulmonary artery measuring
catheter with temperature sensor is additionally required. Before
the beginning of a measurement, the temperature sensor connector of
the central vein catheter is connected to a device processing the
associated algorithm (cf. FIG. 5); then the measurements are
carried out.
61. FIG. 4 shows a diagrammatic longitudinal sectional view of a
device for determining the instant of injection and the duration of
injection in thermodilution measurements according to the present
invention. In such thermodilution measurements, an injectate fluid
at a temperature deviating from the temperature of the blood of a
patient is injected at a specific injection site into a blood
vessel of the patient and the temperature of the blood is measured
at a measuring site downstream of the injection site.
62. For this purpose, the device has an extracorporeal,
small-volume sensor housing 12 of transparent plastic, which is
provided proximally with an input connection in the form of a
female Luer lock connection 11a, which can be connected to an
injectate source, and distally with an output connection in the
form of a male Luer lock connection 11b, which can be connected to
a blood vessel catheter.
63. Recessed centrally into the sensor housing 12 there is a
temperature sensor 13, which continuously senses the temperature in
a region between the input connection 11a and the output connection
11b and protrudes into the lumen of the sensor housing 12. By means
of a suitable connector, the temperature signal picked off here can
be passed on via a line 15 to a measuring computer.
64. The sensor housing 12 is integrated into a heat contact plate
10 of skin-compatible, heat-conducting material, which is designed
as an adhesive plate 10 and accordingly can be fastened directly on
the skin 9 of the patient.
65. On the side facing away from the body, the sensor housing 12 is
provided toward the ambient air with a heat-insulating layer 14. In
this way, the fluid in the sensor housing 12 is warmed up by the
heat given off by the patient, to be precise distinctly above room
temperature, depending on the skin temperature, fastening site and
spatial conditions (for example intensive care unit, operating
room), according to experience in the case of normothermic patients
by distinctly more than 2 degrees Celsius. Thus, in spite of
extracorporeal or extravasal localization of the temperature sensor
13, there occurs a distinct temperature difference between the
injectate at room temperature and the dead space, with the result
that a reliable detection of the injection is ensured in this case
as well.
66. With regard to the application, it should be noted that, after
a central vein or pulmonary artery catheter has been placed by the
Seldinger technique, the device represented in FIG. 4 is fitted
proximally onto the injection system and distally onto the
injection lumen of the central vein or pulmonary artery catheter by
means of the Luer lock connections 11a and 11b, respectively, after
proper venting. For a transcardiopulmonary thermodilution, the
corresponding catheter is placed into the Arteria femoralis/Arteria
radialis.
67. The line 15 for transferring the temperature signal is fastened
by means of a suitable connector on the temperature sensor 13 and
is connected to a device processing the corresponding algorithm
(cf. FIG. 5). Subsequently, the measurements are carried out.
68. An exemplary embodiment which is not represented in the figures
largely corresponds to the exemplary embodiment according to FIG.
4. In addition, here there is provided a device for the externally
activated warming up or cooling of the temperature sensor. This is
necessary in situations in which the patient does not provide
adequate body heat of his/her own, for example during operations in
deep hypothermia. The sensor temperature deviates distinctly from
room temperature by means of a control mechanism integrated in the
associated device.
69. The use of the temperature sensors known from the prior art led
to the patient being given injectate at three temperatures via the
injection lumen of the catheter; these were
70. a) the intracorporeal dead space at body temperature,
71. b) the extracorporeal volume at room temperature and
72. c) the cooled bolus at distinctly less than room temperature.
In contrast to this, in the device according to the present
invention the extracorporeal volume and the bolus have the same
temperature, with the result that overall only two temperatures
occur in the essential volumes which contribute to the injected
amount of heat. Accordingly, the injected amount of heat can be
determined more accurately, with the result that possible error
sources of a thermodilution are reduced.
73. In the exemplary embodiment according to FIG. 4, it can be
ignored here that the minimal volume of the sensor housing 12 is
warmed slightly with respect to room temperature. As in the other
exemplary embodiments as well, the heat source, for example body
heat, or the heat sink, is utilized for determining the instant of
injection and duration of injection, which takes place with the aid
of the following algorithm (cf. FIG. 5):
74. 1. Monitor continuously the temperature at the injectate
sensor, which for this purpose is fed into the measuring device,
and calculate progressively the mean value T.sub.0 and the standard
deviation S of the temperature.
75. 2. If the temperature deviates in about one second by more than
about 0.25 degree Celsius, but at least by a multiple of the
standard deviation S, from the mean value T.sub.0, the beginning of
injection is detected at this instant t.sub.a and the procedure is
continued with step 3. Otherwise, go back to step 1.
76. 3. Continue recording the temperature until it again tends
toward the mean value T.sub.0. There is subsequently at least one
local extreme T.sub.min of the injectate temperature.
77. 4. Continue measuring the temperature for a short period of
time, for example for one second, and determine the global extreme
of the temperature T.sub.g since the beginning of injection, where
sign(T.sub.0-T.sub.g)=sign(T.sub.0- T.sub.min). Here, sign(x) is
the sign function with sign(x) =1 for x>0 and sign(x)=-1 for
x<0.
78. 5. If sign(T.sub.0-T.sub.g) * T.sub.g is less than or equal to
sign(T.sub.0-T.sub.min) * T.sub.min, then make T.sub.min=T.sub.g
and continue with step 4, with the result that short-term
fluctuations of the injectate temperature do not disturb the search
for the extreme. Otherwise, proceed to step 6.
79. 6. Register the temperature until it again reaches
T.sub.0-.alpha. * (T.sub.0-T.sub.min). In this, .alpha. lies
between zero and one and may either be assumed to be constant or
calculated from the standard deviation S.
80. 7. The last recorded temperature data are used to determine the
instant t.sub.e since when the temperature has been tending toward
to in a strictly monotonic function over time. The instant t.sub.e
is the sought end of injection, with the result that the duration
of injection can be calculated with t.sub.e-t.sub.a and the average
injectate passage time can be calculated with
t.sub.a+(t.sub.e-t.sub.a)/2=(t.sub.a+t.sub.e)- /2.
81. 8. Since the minimum temperature T.sub.min of the sensor does
not exactly reproduce the injectate temperature T.sub.inj, in
particular in the case of injection of short duration, an
algebraically or exponentially falling function, for instance
T.sub.inj+(T.sub.0-T.sub.inj- ) * exp(-(t- t.sub.a)/.tau.), can be
made to fit the injection curve for times t from the interval
[t.sub.a, t.sub.e], by determining the parameters T.sub.inj and
.tau.. If, for example to save computing time, no fit is carried
out, to simplify matters T.sub.inj= T.sub.min is set.
82. With the aid of the computing specification given in steps 1 to
8, the variables sought, instant of injection, duration of
injection and injectate temperature, are determined simultaneously
with the data acquisition. However, while maintaining the essential
computing steps, the algorithm may also be modified such that the
injection parameters sought are determined only after the
temperature measurement. The procedure may also be extended such
that the duration of injection must not exceed a predetermined time
period, for example of six seconds, and accordingly the algorithm,
in particular steps 4 and 5, cannot be endlessly repeated and a
termination can be ensured.
83. All the systems illustrated in the exemplary embodiments, that
it to say both the intravasal injectate temperature sensor
integrated in the catheter and the heat-insulated extracorporeal
injectate temperature sensor housing, with or without external heat
source or heat sink, ensure a reliable detection and determination
of the instant of injection and the duration of injection in
measurements of the hemodynamics with injectate kept at room
temperature. In this way, the measuring procedure is facilitated,
the costs, for example for expensive cooling sets, are lowered and
the attentiveness of the physician to the patient is not adversely
affected.
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