U.S. patent application number 11/836386 was filed with the patent office on 2007-11-29 for system for detecting the status of a vent associated with a fluid supply upstream of an infusion pump.
This patent application is currently assigned to CARDINAL HEALTH 303, INC.. Invention is credited to ROBERT D. BUTTERFIELD, TIMOTHY W. VANDERVEEN.
Application Number | 20070274843 11/836386 |
Document ID | / |
Family ID | 34711062 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070274843 |
Kind Code |
A1 |
VANDERVEEN; TIMOTHY W. ; et
al. |
November 29, 2007 |
SYSTEM FOR DETECTING THE STATUS OF A VENT ASSOCIATED WITH A FLUID
SUPPLY UPSTREAM OF AN INFUSION PUMP
Abstract
A system and method for determining whether the pressure in a
fluid line upstream of an infusion pump is becoming lower as
pumping draws fluid from the fluid line and fluid container due to
a lack of proper venting. An initial pressure is sensed by an
upstream pressure sensor at the start of an infusion. After a
period of time, which may be determined either by monitoring
infusion time or the number of pump cycles completed, a second
pressure is sampled and compared to the initial pressure. Various
analytical methods may be applied to the sensed pressures to
determine upstream pressures or trends. Where an upstream pressure
reading indicates a lack of proper venting, an alert signal is
provided. Continuous monitoring may occur in which succeeding
samples are compared to preceding samples to determine upstream
pressures or trends.
Inventors: |
VANDERVEEN; TIMOTHY W.;
(POWAY, CA) ; BUTTERFIELD; ROBERT D.; (POWAY,
CA) |
Correspondence
Address: |
FULWIDER PATTON LLP
HOWARD HUGHES CENTER
6060 CENTER DRIVE, TENTH FLOOR
LOS ANGELES
CA
90045
US
|
Assignee: |
CARDINAL HEALTH 303, INC.
SAN DIEGO
CA
|
Family ID: |
34711062 |
Appl. No.: |
11/836386 |
Filed: |
August 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10749367 |
Dec 31, 2003 |
7255683 |
|
|
11836386 |
Aug 9, 2007 |
|
|
|
Current U.S.
Class: |
417/63 ;
417/53 |
Current CPC
Class: |
A61M 5/14228 20130101;
A61M 5/16854 20130101; A61M 2205/3351 20130101; A61M 2205/18
20130101 |
Class at
Publication: |
417/063 ;
417/053 |
International
Class: |
F04B 49/10 20060101
F04B049/10 |
Claims
1. A system for detecting the status of a vent associated with a
fluid supply upstream of an infusion pump, comprising: a pressure
sensor located upstream of an infusion pump, the pressure sensor
configured to provide pressure signals representative of the
pressure within a fluid line; a processor configured to monitor a
parameter representative of a status of the infusion pump and to
sample the pressure signals received from the pressure sensor as a
function of the status of the infusion pump, and, if the sampled
signals indicate a negative pressure in the fluid line, to provide
an alert.
2. The system of claim 1 wherein the infusion pump is a peristaltic
pump and the monitored parameter is a value of the number of pump
cycles the peristaltic pump has completed.
3. The system of claim 2 wherein the processor samples the signals
received from the pressure sensor when the value of the monitored
parameter exceeds a predetermined number of pump cycles.
4. The system of claim 2 wherein the processor periodically samples
the signals received from the pressure sensor after a predetermined
number of pump cycles have occurred.
5. The system of claim 4 wherein the predetermined number of pump
cycles is three.
6. The system of claim 1, wherein the negative pressure is
indicative of a vent problem.
7. A method of determining the status of a vent in a fluid line
located upstream of a peristaltic infusion pump, the peristaltic
infusion pump configured to pump fluid in a cyclical manner, the
method comprising: determining a value representative of the number
of cycles that the have been completed by the infusion pump;
sampling signals provided by a pressure sensor configured to sense
the pressure in a fluid line upstream of the infusion pump;
processing the signals to determine a value for the pressure in the
upstream fluid line; and providing an alert if the pressure value
is negative.
8. The method of claim 7 wherein sampling occurs only when a
predetermined number of pump cycles have been completed.
9. The method of claim 7 further comprising: storing the value for
the pressure in a memory; sampling the signals after and
predetermined number of cycles have been completed; determining a
second value for the pressure in the upstream fluid line; comparing
the second value for the pressure to the first value for the
pressure; and providing an alert signal if the second value is more
negative than the first value.
10. A system for detecting a change in pressure in an infusion line
upstream of an infusion pump, comprising: a pressure sensor located
upstream of an infusion pump adjacent an upstream infusion line,
the pressure sensor configured to provide pressure signals
representative of the pressure within the upstream fluid line; and
a processor programmed to monitor a parameter representative of a
status of an infusion of fluid into a patient, the processor also
programmed to sample pressure signals received from the pressure
sensor as a function of the status of the infusion, and to analyze
the sampled signals to determine if the pressure in the upstream
fluid line is decreasing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a system and
method for detecting when a negative-going pressure exists in an
infusion line or container upstream of an infusion pump during
administration of an infusion fluid to a patient. More
specifically, the present invention relates to a system
incorporating a container-side pressure sensor for sensing
negative-going changes in the pressure within a fluid line, and for
monitoring the container-side pressure to prevent negative-going
pressure from developing due to an un-opened or blocked vent.
[0003] 2. General Background and State of the Art
[0004] A common problem during infusion of therapeutic fluids into
a patient occurs when the fluid to be infused is contained in
burettes, bottles, or other non-flexible or partly flexible
containers. When containers such as these are used as fluid
reservoirs, they must be vented while the infusion is ongoing. If
they are not vented, as fluid is drained from the bottle, burette,
or other relatively rigid container, negative pressure is created
within the container. This negative pressure may cause a reduction
in flow, leading to inaccurate delivery of the therapeutic
fluid.
[0005] Where an infusion pump is used to infuse the therapeutic
fluid, the negative pressure building inside the container may also
increase strain on the infusion pump, and may cause the pump to
sound an alarm if the desired fluid infusion rate cannot be
maintained. Another problem that can occur is that the negative
pressure may result in air ingress into the system, especially at
joints in the infusion line before the infusion line enters the
infusion pump. This may result in air being entrained in the
therapeutic fluid, and subsequently infused into the patient. While
many infusion pumps use various types of air-in-line sensors to
detect such entrained air and either halt the infusion or sound an
alarm requiring attention by a care-giver before an amount of air
that might injure the patient can be infused into the patient,
prevention of such an occurrence is more cost-effective and
efficient. Moreover, in cases where thin walled, yet rigid
containers are used, the negative pressure may increase to such an
extent that the thin walled containers collapse, possibly spilling
their contents.
[0006] A vent is typically used in systems that will be infusing
fluids from bottles, burettes, or other rigid or semi-rigid
containers to prevent the build up of negative pressure as the
fluid is drained from the container. However, if a care-giver
forgets to open the vent or the particular drug or combination of
drugs being infused wets the vent, the vent will not allow passage
of air, resulting in a progressively increasing negative pressure
in the container and fluid line as the pump attempts to draw fluid
from the container.
[0007] What has been needed, and heretofore unavailable, is a
system and method for determining when a container that requires
venting to function properly is not being vented appropriately.
Such a system would be able to detect the onset of negative
pressure early enough so that a signal could be provided to
care-givers before the infusion became inaccurate or damage was
done to the pump. Moreover, such a system would be able to
determine whether the intake or container-side pressure is not
changing over time, indicating a stable infusion rate, or is
decreasing as fluid is removed from the container, indicating lack
of proper venting requiring attention by the care-giver. The
present invention satisfies these and other needs.
INVENTION SUMMARY
[0008] Briefly and in general terms, the present invention is
directed to a system and method for detecting when a container is
not vented properly, leading to the formation of a reduced or
negative-going pressure in a fluid line upstream of an infusion
pump. It its broadest aspect, the present invention is embodied in
an infusion pump that includes a sensor for detecting the pressure
of fluid in the intake fluid line upstream of the infusion
pump.
[0009] In another aspect, the present invention comprises an
infusion pump system having a processor that monitors signals
received from a sensor configured to monitor the pressure within
the intake fluid line upstream of the infusion pump, and the
processor also monitors a peristaltic pump within the infusion pump
to track the status or position within its pumping cycle. In a
further aspect, the processor samples the intake pressure multiple
times each pumping cycle to compute a cycle-average, tracks the
number of pumping cycles completed by the peristaltic pump, and
processes the cycle-average pressures after a predetermined number
of pump cycles have been completed. In a further aspect, the
cycle-average pressure is sampled each time a selected number of
pump cycles have been completed. After sampling the signals from
the upstream pressure sensor, the processor determines whether
there is a negative-going pressure present in the upstream infusion
line.
[0010] In yet another aspect of the present invention, if the
processor determines that a negative-going pressure is present in
the upstream infusion line, the processor may direct that an alert
be provided to care-givers notifying them that the infusion set-up
requires attention. Such an alert may be visual, such as, for
example, a message on a display, a blinking light, or a change in
the color of text on a display. In another aspect, the alert may be
auditory, such as an alarm. In still another aspect, the alert may
take the form of a printed report. In still another detailed
aspect, a combination of visual and auditory alerts may be
provided. Where the infusion pump is in communication with other
systems, such as an institution hospital administration system,
patient monitoring system or the like, the alert may be recorded in
a data base of alerts, and/or it may be associated and stored in a
patient's medical administration record ("MAR").
[0011] In still another aspect of the present invention, the sensed
intake pressure may be stored in a memory accessible by the
processor. In yet a further aspect, the processor may wait a
selected number of pump cycles, and, at the conclusion of the
selected number of pump cycles, sample the cycle-average sensor
signals and determine a second, later, cycle-average pressure value
for the pressure in the upstream fluid line. The processor may then
compare the second, later, cycle-average pressure value with the
earlier pressure value to determine if there is a negative-going
pressure in the fluid line. The processor may employ the slope of
the cycle-average intake pressure signal versus time as well as its
gauge value in determining whether a fault condition is present.
The processor may then issue an alert indicating that attention to
the infusion set-up is required.
[0012] In yet another aspect in accordance with the invention, a
system for detecting the status of a vent associated with a fluid
supply upstream of an infusion pump is provided, comprising an
intake pressure sensor located upstream of an infusion pump, the
intake pressure sensor configured to provide pressure signals
representative of the pressure within the intake fluid line, and a
processor configured to monitor a parameter representative of a
status of the infusion pump such as the position of the mechanism
within its pumping cycle and to sample the pressure signals
received from the pressure sensor as a function of the status of
the infusion pump, and, if the sampled signals indicate a
negative-going pressure in the fluid line, to provide an alert. In
yet another aspect, the negative-going cycle averaged pressure is
indicative of a vent problem.
[0013] In still another aspect, the present invention includes a
system wherein the infusion pump is a peristaltic pump and the
monitored parameter is both the position within the peristaltic
mechanism cycle and a value of the number of pump cycles the
peristaltic pump has completed. In yet another aspect, the
processor samples the signals or the cycle-average of the pressure
signals received from the pressure sensor when the value of the
monitored parameter exceeds a predetermined number of pump
cycles.
[0014] In a further aspect, the processor periodically samples the
cycle-average pressure signal received from the pressure sensor
after a predetermined number of pump cycles has occurred. In one
embodiment, the predetermined number of pump cycles is three.
[0015] In another aspect, the present invention includes a method
of determining the status of a vent in a fluid line located
upstream of a peristaltic infusion pump, the peristaltic infusion
pump configured to pump fluid in a cyclical manner, the method
comprising determining a value representative of the number of
cycles that the have been completed by the infusion pump, sampling
cycle-averaged pressure signals provided by a pressure sensor
configured to sense the pressure in a fluid line upstream of the
infusion pump, processing the cycle-averaged pressure signals to
determine a value for the pressure in the upstream fluid line, and
providing an alert if the rate of change of the cycle-averaged
pressure exceeds a limit which may be a fixed value or a function
of the size and type of container provided to the pump's control
system via the control interface. In another aspect, the sampling
of the cycle-average pressure occurs only when a predetermined
number of pump cycles have been completed.
[0016] In a further aspect of the present invention, the method
includes storing the value of the cycle-average pressures in a
memory, sampling the cycle-averaged pressures after a predetermined
number of cycles have been completed, determining a second
cycle-averaged value for the pressure in the upstream fluid line,
comparing the second value for the pressure to the first value for
the pressure, and providing an alert signal if the second value is
more negative than the first value by an amount either preset or a
function of the container size and type provided to the pump's
control system via the control interface.
[0017] In yet another aspect, the present invention is directed to
a system for detecting a change in pressure in an infusion line
upstream of an infusion pump, comprising a pressure sensor located
upstream of an infusion pump adjacent an upstream infusion line,
the pressure sensor configured to provide pressure signals
representative of the pressure within the upstream fluid line, and
a processor programmed to monitor a parameter representative of a
status of an infusion of fluid into a patient, the processor also
programmed to sample pressure signals received from the pressure
sensor as a function of the status of the infusion, and to analyze
the sampled signals to determine if the pressure in the upstream
fluid line is decreasing.
[0018] Other features and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings, which illustrate, by
way of example, the features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 depicts an infusing set-up including a fluid source
and an infusion pump for infusing fluid from the fluid source into
a patient.
[0020] FIG. 2 is a side view of an exemplary peristaltic infusion
pump including an upstream pressure sensor.
[0021] FIG. 3 is a schematic diagram of one embodiment of an
infusion pump control system capable of being programmed to carry
out the methods of the present invention.
[0022] FIG. 4 is a block diagram of an embodiment of the methods of
the present invention directed to detecting a reduced pressure in
an upstream fluid line or container.
[0023] FIG. 5 is a block diagram of an alternative embodiment of
the methods of the present invention directed to detecting a
reduced pressure in an upstream fluid line or container.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring now to the drawings wherein like reference
numerals among the drawing represent like or corresponding
elements, there is shown in FIG. 1 an infusion pump set-up,
generally designated by numeral 10, shown in use in its intended
environment. In particular, the infusion pump set-up 10 is shown
attached to an intravenous (I.V.) pole 12 on which a fluid source
14 containing an I.V. fluid is held. The fluid source 14 is
connected in fluid communication with an upstream fluid line 16.
The fluid line 16 is a conventional I.V. infusion-type tube
typically used in a hospital or medical environment and is made of
any type of flexible tubing appropriate for use to infuse
therapeutic fluids into a patient, such as polyvinylchloride (PVC).
A pumping tube segment 18 formed of flexible tubing is mounted in
operative engagement with a peristaltic pump pumping apparatus 19,
for pumping fluid through a downstream fluid line 20 into a
patient's arm 22. It will be understood by those skilled in the art
that the upstream fluid line 16, the flexible pumping portion 18,
and the downstream fluid line 20 may be portions of a continuous
length of flexible tubing, with the portions defined by the
location of the peristaltic pump 19. For convenience, the entire
length of tube shown in FIG. 1 is indicated by reference numeral
21. In this context, the term "upstream" refers to that portion of
the flexible tubing 21 that extends between the fluid source 14 and
the peristaltic pump 10, and the term "downstream" refers to that
portion of the flexible tubing 21 that extends from the peristaltic
pump 10 to the patient 22.
[0025] FIG. 2 depicts an enlarged view of the infusion pump 10
showing the interaction of the fluid line 21 with the elements of
the peristaltic infusion pump. The fluid line 21 is disposed in the
housing 30 of the pump 10 in such a manner that the flexible
pumping portion 18 is in releasable contact with one or more
pumping fingers 40 of the peristaltic infusion pump. Typically,
such a peristaltic infusion pump utilizes a camshaft 35 with
rotating cams, or other mechanism, to actuate one or more of the
fingers 40 so that the fingers 40 sequentially press upon and
squeeze the flexible portion 18 of the tube 21 to force fluid
within the tube in a downstream direction. The operation of
peristaltic mechanisms is well known to those skilled in the art
and no further details are provided here.
[0026] An upstream intake pressure sensor or detector 50 is mounted
in the housing 30 of the pump 10 to monitor the fluid pressure
within the upstream, or container-side, tube 16. The upstream
intake pressure sensor 50 may be any kind of detector known in the
art that is capable of monitoring the fluid pressure within the
tube 16 and providing signals that may be received by suitable
electronics, such as, for example an amplifier, A/D converter,
digital storage medium, such as a flash memory, or other type of
suitable storage medium for storing values representative of the
signals provided by the sensor. The digitized signals may also be
provided to a computer or microprocessor for analysis, display, or
reporting. Examples of pressure sensors or detectors suitable for
monitoring the pressure within an upstream infusion line are
capacitive, semiconductor, or resistive strain gauges,
piezo-electric detectors, or other sensors or detectors known to
those skilled in the art.
[0027] Those skilled in the art will also understand that the
upstream intake pressure sensor and method embodied in the present
invention are equally applicable to a rotary peristaltic or other
cyclic infusion pump mechanisms, and such is intended to be within
the scope of the present invention. Moreover, while the present
invention is described in relation to an infusion pump having a
processor or computer associated with the pump, it is intended that
the invention also include systems wherein the microprocessor or
computer is remote from, but in communication with the pump.
[0028] Generally, as shown in FIG. 3, the infusion pump will
include a control system 70 configured or programmed to control the
operation of the peristaltic infusion pump so that a prescribed
amount of medication or other therapeutic fluid is infused into the
patient over a desired period of time. Such control systems
typically include a microprocessor 75, a memory 80 associated with
the microprocessor 75, one or more inputs 85 for inputting signals
to the microprocessor, and one or more outputs 90 for outputting
signals from the microprocessor.
[0029] The control system 70 may also be in communication with
information systems, such as a pharmacy information system,
hospital administration system, or other such systems in the
institution using an input/output port 92 and communication means
95. The input/output port 92 may be any port configured to send and
receive data using appropriate communication protocols, such as
RS232 and the like. For example, the input/output port 92 may be a
serial port, a parallel port, a USB, or other suitable port. It
will also be understood that the input 85 and the output 90 may be
combined in such a manner that all signals to and/or from the
processor 75 are communicated through one or more input/output
ports 92, rather than through separate inputs and outputs.
[0030] The communication means 95 may be a hard wired or wireless
connection to another computer, a local area network, a wide area
network, a telephone line to a remote server or client system, or
the internet. The communication means may include specialized
connection devices for connecting to optical fiber, coaxial cable,
Ethernet cabling, or other communication lines. Alternatively,
wireless connections may be used, which may also include the use of
suitable transmitters and receivers as is known in the art. Such
wireless connectivity may include use of infra red, RF, Bluetooth,
or WiFi (IEEE 802.11b) communication means and the like.
Additionally, the microprocessor 75 is commonly programmed using
either embedded programming instructions or suitable software so
that the microprocessor can carry out the tasks desired of it.
[0031] In one embodiment of the system and method of the present
invention, the microprocessor 75 is capable of receiving signals
from an upstream intake pressure sensor 105 through the input 85.
The upstream intake pressure sensor 105 is disposed adjacent an
upstream infusion line so as to monitor the fluid pressure within
the upstream infusion line, and provide signals representative of
the sensed pressure within the infusion line to the microprocessor
75. The microprocessor 75, as described above, is programmed using
appropriate software or embedded commands to analyze the signals
received from the upstream pressure sensor 50. After the analysis
of the received upstream pressure signals is completed, the
processor may output a signal through the output 90. This signal
may be directed to the pump motor 115 to control the infusion of
fluid to the patient.
[0032] The signal may also be directed to a display 120 to inform
an operator of the status of the pump and/or the pressure within
the upstream infusion line. This display may also include a means
of providing a visual alert, such as a flashing display, blinking
light, or a change in text color on the display to alert an
operator that the infusion set-up requires attention.
[0033] The signal may also be directed to an alert module 125. This
alert module may be a separate module of the processor that is
controlling the pump, or it may be located at a location remote
from the pump, and/or associated and in communication with a
separate processor remote from the pump. The alert module 125 may
be configured to provide visual, auditory, or a combination of
visual and auditory notifications to care givers to alert the care
giver that attention must be given to the infusion system. The
alert module may produce signals that are communicated to consoles
at the bed side, the nurse station, or a centrally located
monitoring system. Additionally, various combinations of display
changes and auditory alerts may be used to signify a priority of an
alert, so that alerts which do not require immediate attention are
less noticeable than alerts that require immediate attention to
correct a problem before harm to the patient being infused can
occur.
[0034] The alert module 125 may also provide signals representing
the progress of the infusion, including any alerts generated due to
a sensed reduced or negative pressure in the upstream infusion
line, to a data base where the information is stored for later
inspection and analysis. The data base may be associated with the
pump, or the data base may be remote from the pump 10. For example,
where the pump is controlled by a remote control system, the data
base may be located and associated with the remote control system.
In another embodiment, the data base may be part of an
institutional information system which may be part of an enterprise
wide network.
[0035] In another embodiment, the microprocessor 75 may also be
configured to receive signals from a pump mechanism position sensor
110 through the input 85. In this embodiment, the processor 75 may
monitor the function of the pump 10, collecting, analyzing, and
storing information related to the infusion, such as, for example,
the start time and completion time of the infusion, the amount of
fluid infused, and the number of pump cycles that have been
completed since the start of the infusion or since a selected time
in the past and the intake pressure values at each of a plurality
of corresponding pump mechanism positions. This information may be
stored in the memory 80 for later retrieval and analysis, or the
information may be communicated to another, remote, system using
the communication means 95.
[0036] FIG. 4 is a schematic block diagram 200 illustrating one
embodiment of the method of the present invention performed by the
processor to determine the pressure in an upstream infusion line
and to determine whether an alert should be given signifying that a
negative pressure is building up in the upstream infusion line at a
rate in excess of that expected under normal venting conditions. As
discussed above, the processor is programmed to perform, among
other processes, the steps set forth in FIG. 4. When the care-giver
or operator starts the infusion by activating the infusion pump in
box 205, the processor samples the signals representative of the
pressure within the upstream infusion line provided by an upstream
pressure sensor (FIG. 2) in box 210, converts the sampled signals
into a pressure, and stores the pressure and the associated
mechanism position (typically represented as an index, a step
number or a rotational angle) in a memory associated with the
processor (FIG. 3) in box 215.
[0037] The processor then computes the cycle-average pressure from
the plurality of samples obtained from each individual cycle,
monitors the elapsed pumping time in box 220 and waits for a
selected period of time, which may be determined by the processor
as being the time necessary for a selected number of processor
clock cycles to occur, or some other measure of time determined
from the operational characteristics of the processor, based on,
for example, the clock speed of the processor as is well known in
the art. After the pre-determined time period has elapsed or a
specific movement of the mechanism detected, as determined in box
225, the processor may again sample the signals from the upstream
pressure sensor in box 230, convert the sampled signals into a
pressure value, convert these samples to a cycle-average pressure
and compare the second cycle-average pressure value with the stored
cycle-average pressure value in box 235 to determine if there has
been an change in the pressure present in the upstream infusion
line. If the predetermined period of time or movement has not
elapsed or occurred, the processor continues to monitor the elapsed
pumping time or motion, as depicted in box 220.
[0038] If the second cycle-averaged pressure value is less than the
first cycle-averaged pressure value by more than a predetermined
value or a value associated with the size and type of container as
entered from the pump's user interface, the processor determines
that an alert should be given to the care-giver, and provides that
alert in box 240 by providing a visual or auditory alarm or notice
that a fault condition exists and that the care-giver should
inspect the infusion set-up and take appropriate corrective action,
such as opening or unblocking a vent in upstream infusion line or
container. If the comparison of the latter cycle-average pressure
to the earlier cycle-average pressure does not indicate an excess
reduction of pressure in the upstream infusion line, the processor
returns to box 215 and stores the latest cycle-average pressure in
the memory.
[0039] The processor may be programmed so that the process
described above is carried out continuously throughout the
infusion, providing a fail safe system to ensure proper venting of
the upstream infusion line and fluid container. In such an
embodiment, after the latest pressure value is stored in the memory
in box 215, the processor continues to monitor the elapsed pumping
time for an additional period, carrying out the remaining steps as
set forth above for each pumping time interval.
[0040] When the latest cycle-average value of the upstream pressure
is stored in the memory, the memory of the earlier value or values
may simply be overwritten, or alternatively, the memory may be
configured to store all of the pressure values determined during
the infusion for later analysis. Multiple sequential cycle-average
values may be used in conjunction with a digital weighting
algorithm to compute an optimized slope of the cycle-average
pressure signal which spans more than two cycles and thereby is
more resistant to the effects of movement and other types of
environmental artifact. Where all, or at least a portion, of the
pressure values are stored, they are stored in a manner such that
they are available to the processor in sequential order, so that
the processor may compare the latest pressure value to the next
earlier pressure value and/or perform more complex slope analysis
as discussed above.
[0041] In another embodiment of the present invention, as depicted
in FIG. 5, the processor may determine the time frame for sampling
the signals from the upstream pressure sensor by monitoring the
number of pump cycles completed by the infusion pump. When the
care-giver or operator starts the infusion by activating the
infusion pump in box 255, the processor samples the signals
representative of the pressure within the upstream infusion line
provided by an upstream pressure sensor in box 260, converts the
sampled signals into a pressure, averages multiple pressure samples
associated with a mechanism cycle, and stores the cycle-average
pressure in a memory associated with the processor in box 265.
[0042] The processor then monitors the number of pump cycles in box
270. If the pump has completed a selected number "N" cycles, as
determined in box 275, then the program branches to box 280, and
the signals from the upstream pressure sensor are again sampled,
and the new cycle-average pressure value is compared to latest
stored cycle-average pressure value in box 285 to determine the
difference. If the selected number of cycles has not been
completed, the program returns to box 270 and continues to monitor
the number of pump cycles until the selected number of cycles is
completed, then branching to box 280.
[0043] If the pressure sampled in box 280 is determined in box 285
to be less than the stored pressure value by more than an allowed
maximum, the processor directs that an alert signal be provided in
box 290. If the comparison in box 285 indicates that the latest
sampled pressure is equal to or greater than the stored pressure,
indicating that the pressure in the upstream line is stable or not
reduced, then the program branches to box 265, stores the latest
sampled pressure in the memory, and continues to monitor the number
of pump cycles in box 270 until the next time that the upstream
pressure should be sampled.
[0044] Alternatively, the processor may sample the cycle-averaged
pressure difference values stored in the memory over a selected
period of time and calculate, for example, an average value over
the period of time to compare with the latest pressure value. One
example of an analysis of this type is commonly called a moving
average, which may be weighted or un-weighted, as those terms are
understood in the art. In this manner, momentary changes in
pressure, or errors in the signals provided by the upstream
pressure sensor, may be filtered out to prevent unnecessary alarms.
Other analysis methods, such as trend analysis or other methods may
be utilized to ensure that alerts due to insignificant pressure
changes or erroneous signals from the upstream pressure sensor are
minimized while still providing protection from significantly
reduced or negative pressure in the upstream infusion line.
[0045] While several particular forms of the invention have been
illustrated and described, it will be apparent that various
modifications can be made without departing from the spirit and
scope of the invention.
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