U.S. patent application number 15/224038 was filed with the patent office on 2016-11-17 for syringe pump rapid occlusion detection system.
This patent application is currently assigned to SMITHS MEDICAL ASD, INC.. The applicant listed for this patent is SMITHS MEDICAL ASD, INC.. Invention is credited to ZHAN LIU, BRIAN POPE.
Application Number | 20160331895 15/224038 |
Document ID | / |
Family ID | 34435522 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160331895 |
Kind Code |
A1 |
POPE; BRIAN ; et
al. |
November 17, 2016 |
SYRINGE PUMP RAPID OCCLUSION DETECTION SYSTEM
Abstract
An apparatus, method and program product detects an occlusion in
a fluid line by determining if a relationship between force
measurements departs from an expected relationship.
Inventors: |
POPE; BRIAN; (SUWANEE,
GA) ; LIU; ZHAN; (FREMONT, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SMITHS MEDICAL ASD, INC. |
PLYMOUTH |
MN |
US |
|
|
Assignee: |
SMITHS MEDICAL ASD, INC.
PLYMOUTH
MN
|
Family ID: |
34435522 |
Appl. No.: |
15/224038 |
Filed: |
July 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13449355 |
Apr 18, 2012 |
9427521 |
|
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15224038 |
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10700738 |
Nov 4, 2003 |
8182461 |
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13449355 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M 5/1452 20130101;
A61M 2205/505 20130101; A61M 2205/3569 20130101; A61M 5/16854
20130101; A61M 5/5086 20130101; A61M 5/16859 20130101; A61M
2005/16863 20130101; A61M 2205/52 20130101 |
International
Class: |
A61M 5/168 20060101
A61M005/168; A61M 5/50 20060101 A61M005/50; A61M 5/145 20060101
A61M005/145 |
Claims
1. A method of automatically detecting an occlusion in a fluid line
of an infusion pump, the method comprising: pumping fluid through a
fluid line of an infusion pump, the pumped fluid flows through the
fluid line at a first rate; detecting a first pressure of fluid
within the fluid line at a first time; altering the pumping of
fluid through the fluid line if the first pressure surpasses a
threshold pressure value; detecting a second pressure of fluid
within the fluid line at a second time; automatically resuming the
pumping of fluid through the fluid line if the second pressure does
not surpass the threshold pressure value; and wherein the pumping
of fluid through the fluid line is resumed such that the fluid
flows through the fluid line at a second rate that is less than the
first rate.
2. The method of claim 1, further comprising: allowing at least a
predetermined time period to elapse between the first time and the
second time.
3. The method of claim 1, further comprising: providing an
indication of an occlusion if the second pressure surpasses the
threshold pressure value.
4. The method of claim 1, further comprising: determining if a
bolus infusion is indicated.
5. The method of claim 4, wherein determining if a bolus infusion
is indicated occurs after altering the pumping of fluid through the
fluid line.
6. The method of claim 5, further comprising: generating an
occlusion alarm if a bolus infusion is not indicated.
7. The method of claim 1, wherein altering the pumping of fluid
through the fluid line includes stopping the pumping of fluid
through the fluid line.
8. A medical infusion pump comprising: a pump configured to
generate a pressure in a fluid line to advance fluid in the fluid
line from a fluid source to the patient; a sensor configured to
sense a value indicative of pressure in the fluid line; a processor
configured to monitor for an occlusion in the fluid line using an
input from the sensor; memory configured to store computer
executable instructions; and wherein the processor is configured to
execute the computer executable instructions to: detect a first
pressure of fluid within the fluid line at a first time, wherein
the fluid is traveling through the fluid line at a first rate;
alter pumping of fluid through the fluid line if the first pressure
surpasses a threshold pressure value; detect a second pressure of
fluid within the fluid line at a second time; resume pumping fluid
through the fluid line at a second rate that is less than the first
rate if the second pressure does not surpass the threshold pressure
value.
9. The medical infusion pump of claim 8, wherein resuming pumping
fluid through the fluid line at a second rate that is less than the
first rate occurs automatically if the second pressure does not
surpass the threshold pressure value.
10. The medical infusion pump of claim 8, wherein the processor is
configured to execute the computer executable instructions to allow
at least a predetermined time period to elapse between the first
time and the second time.
11. The medical infusion pump of claim 8, wherein the processor is
configured to execute the computer executable instructions to
provide an indication of an occlusion if the second pressure
surpasses the threshold pressure value.
12. The medical infusion pump of claim 11, wherein providing the
indication includes generating an occlusion alarm if a bolus
infusion is not indicated.
13. The medical infusion pump of claim 8, wherein the processor is
configured to execute the computer executable instructions to
determine if a bolus infusion is indicated.
14. The medical infusion pump of claim 13, wherein determining if a
bolus infusion is indicated occurs after altering the pumping of
fluid through the fluid line.
15. A method of detecting an occlusion in a fluid line extending
through an infusion pump, the method comprising: pumping fluid
through a fluid line with an infusion pump at a first rate of flow;
stopping the pumping of fluid through fluid line if a first
pressure in the fluid line surpasses a threshold pressure value;
resuming the pumping of fluid through the fluid line if a second
pressure in the fluid line does not surpass the threshold pressure
value after at least a predetermined time period has elapsed since
the first pressure in the fluid line surpassed the threshold
pressure value; and wherein the fluid is configured to flow through
the infusion pump at a second rate of flow less than the first rate
of flow when resuming the pumping of fluid through the fluid
line.
16. The method of claim 15, wherein resuming the pumping of fluid
through the fluid line automatically occurs if the second pressure
in the fluid line does not surpass the threshold pressure
value.
17. The method of claim 15, wherein the predetermined time period
is inputted to the infusion pump during setup of the infusion pump
for an infusion application.
18. The method of claim 15, further comprising: generating an alarm
if the second pressure does surpass the threshold pressure
value.
19. The method of claim 15, further comprising: determining if a
bolus infusion is indicated; and generating an alarm if a bolus
infusion is not indicated.
20. The method of claim 19, wherein determining if a bolus infusion
is indicated occurs after stopping the pumping of fluid through
fluid line.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/449,355, filed Apr. 18, 2012, which is a
continuation of U.S. patent application Ser. No. 10/700,738, filed
Nov. 4, 2003, now U.S. Pat. No. 8,182,461, the entire disclosures
of which are incorporated herein by reference.
[0002] This application is also related to U.S. patent application
Ser. No. 13/490,848, filed Jun. 7, 2012, now U.S. Pat. No.
8,900,213, which is a continuation of U.S. patent application Ser.
No. 13/449,355, filed Apr. 18, 2012, the entire disclosures of
which are incorporated herein by reference. It is also related to
U.S. patent application Ser. No. 14/066,112, filed Oct. 29, 2013,
now Publication No. US2014-0058351A1, which is a divisional of U.S.
patent application Ser. No. 13/490,848, filed Jun. 7, 2012, now
U.S. Pat. No. 8,900,213, the entire disclosures of which are
incorporated is herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to drug infusion pumps, and
more particularly, to detecting an occlusion in the fluid path of
such pumps.
BACKGROUND OF THE INVENTION
[0004] The administration of many medications requires specific
dosing regimens that occur over a relatively long period of time.
To this end, the development of syringe pumps has dramatically
benefited patients needing volumetrically proportioned delivery of
their medication. Syringe pumps generally comprise a barrel, or
syringe, and mount to a housing. The syringe is typically filled
with one or more chemical, nutritional or biological substances
that are mixed into a uniform solution. A pusher associated with
the pump forces a plunger through the syringe. As the plunger
travels through the syringe, the medication is forced out into
flexible tubing and/or catheters and into the patient.
[0005] During the course of delivering the medication to the
patient, it is possible for an occlusion to arise in the delivery
path. Examples of occlusions may include a closed stopcock, slider
valve or pinched line. Such a condition, if undetected, may cause
injury to the patient. That is, when an occlusion occurs along the
delivery path, medication is not delivered to the patient even
though the pump continues to function. Thus, an occlusion prevents
the infusion pump from delivering medication to the patient until
the occlusion can be detected and cleared from the infusion path.
For this reason, the rapid detection of occlusions along the
delivery path is key to reliable pump operation.
[0006] An occlusion in the infusion line will cause the force, or
pressure, in the syringe to increase. In turn, force between the
pusher of the syringe pump and the syringe plunger will increase.
Conventional pumping systems use a transducer to monitor force
between the pusher of the syringe pump and the syringe plunger, or
the pressure in the syringe. Other more costly pumping systems
position a disposable sensor within the actual delivery line.
[0007] In such prior art pumps, an alarm is generated when the
force between the pusher and the plunger or the pressure in the
syringe increases above a predetermined threshold. As such, the
alarm is either "on" or "off depending on whether the threshold has
been is met. As a consequence, the user has no way to know whether
the pressure in the syringe is building up to an unacceptable level
that precedes the threshold. The user only knows when the alarm is
reached. Thus, remedial action can only be taken once an infusion
protocol has already been potentially compromised.
[0008] This circumstance is compounded where the threshold is set
to a relatively high value to avoid false occlusion alarms. At low
delivery rates, a conventional pump may take hours to reach high
enough line pressure to trigger conventional alarm systems. This
detection period delay would ideally be around five minutes or less
to avoid having a negative impact on patient care.
[0009] Still another obstacle to occlusion detection arises in the
context of bolus injections, where a relatively large volume of
medication is delivered in a relatively short period of time. In
such bolus applications, the pressure in the pump will easily
exceed the threshold alarm level, irrespective of the presence or
absence of an actual occlusion. Similarly, widely varying pressures
that occur during the initial, ramping stage of a non-bolus
delivery render conventional detection methods unreliable in the
face of varying flow rates. Thus, it is extremely difficult to
detect whether the deliver line is occluded during stages of both
bolus and non-bolus pumping applications.
[0010] As a consequence, there exists a need for an improved manner
of automatically detecting an occlusion within a fluid line with a
medical infusion system.
SUMMARY OF THE INVENTION
[0011] The present invention provides an improved apparatus,
program product and method for automatically detecting an occlusion
in a fluid line of a medical infusion system in a manner that
overcomes the problems of conventional pumps. In one sense, the
invention detects a trend that is indicative of an occlusion much
earlier than is possible with known practices. For example,
processes of the present invention typically allow detection of
closed stopcocks, slider valves, pinched lines and other occlusions
in about five minutes or less (based on a delivery rate of 1 ml/hr
with a 60 ml syringe).
[0012] Such occlusion detection results are made possible using
existing transducers present in most pumps, and thus do not require
additional hardware. Moreover, occlusions are detected under a wide
variety of circumstances and without a propensity of is false
occlusions. To this end, the pressure values of a force sensor are
monitored over time spaced intervals. The pressure values may be
processed to generate a slope, which is compared to value
comprising an expected relationship. If the comparison is
unfavorable, an occlusion alarm is initiated.
[0013] In more particularly determining the presence of an
occlusion, first and second pressure values are obtained at times
T1 and T2, respectively. A relationship between the pressure values
is determined. This relationship typically comprises a slope. An
occlusion is indicated if this relationship between the first and
second pressure values departs from an expected relationship. For
instance, the trial slope determined from the pressure values may
be greater than an occlusion slope recalled from memory. The
recalled slope is optimized for the purpose of detecting an
occlusion as a product of syringe size, type and fluid delivery
rate, among other clinically established factors.
[0014] In accordance with a further aspect of the invention, a
steady state condition of the infusion system is determined to
improve system reliability. Steady state processes consistent with
the principles of the present invention accommodate the wide
pressure variance that occurs during initial ramp up. In so doing,
the steady state processes account for a period of system operation
ranging from the start of an infusion application to some
determinable point where the initial operating stage of the
application should normally have completed.
[0015] If an occlusion occurs after steady state has been achieved,
the slope determined from the pressure values climbs with respect
to time. If this ramp-up in pressure continues for a minimum
duration to the extent it departs from the expected relationship,
the system determines that an occlusion has occurred.
[0016] Another or the same embodiment that is consistent with the
principles of the present invention allows an occlusion to be
detected during a bolus injection, despite the elevated and widely
varying pressure levels associated with such applications. In one
sense, movement of the plunger is halted during a bolus infusion
whenever a detected value deviates from an expected relationship.
Where so desired, the movement of the plunger may continue after
some delay time and/or at a reduced infusion rate. Allowing the
pressure in the system to relax for a period equal to a delay time
limit, in combination with the reduced rate, enables a bolus
infusion in a manner that does not exceed the occlusion limit
and/or initiate a false occlusion alarm. That is, the intermittent
infusion (switch-on/switch-off) bolus feature reduces incidences of
false occlusion, while enabling bolus applications at maximum
infusion rates.
[0017] By virtue of the foregoing, there is thus provided an
improved mechanism for automatically detecting an occlusion in a
fluid line of a syringe pumping system adapted to carry fluid under
pressure to a patient. These and other objects and advantages of
the present invention will be made apparent from the accompanying
drawings and the description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with the general description of the
invention given above and the detailed description of the
embodiments given below, serve to explain the principles of the
present invention.
[0019] FIG. 1 is a block diagram of a syringe pump system
configured to automatically detect an occlusion in a fluid line of
the system.
[0020] FIG. 2 is a block diagram of an exemplary hardware and
software environment for a pump component of the system of FIG.
1.
[0021] FIG. 3 is a flowchart having method steps suitable for
rapidly detecting an occlusion within the system of FIG. 1.
[0022] FIG. 4 is a graph plotting pressure values provided by a
force sensor of FIG. 1.
[0023] FIG. 5 is a table showing exemplary contents of a database
having application within a memory component of FIG. 2.
[0024] FIG. 6 is a flowchart having method steps suited to detect
steady state of the system of FIG. 1.
[0025] FIG. 7 is a flowchart having method steps for determining if
an occlusion alarm step of FIG. 3 should be cancelled.
[0026] FIG. 8 is a flowchart having method steps suitable for
delivering a bolus by the syringe pump system of FIG. 1.
DETAILED DESCRIPTION
[0027] FIG. 1 shows an exemplary syringe pump system 10 configured
to automatically is detect an occlusion. The system 10 shown in
FIG. 1 includes a pharmaceutical cartridge, or syringe 13, which is
supported on and secured by housing 14 and clamp 15, respectively.
The syringe 13 includes a plunger 16 that regulates the flow of
fluid to a patient 24 via infusion line 22. That is, the plunger 16
comprises a piston-type drive mechanism that is internal to the
housing 14 and urges the fluid contents out of an outlet of the
syringe 13 along the infusion line to the patient 24.
[0028] To this end, a motor internal to the housing 14 actuates a
pusher, or plunger driver mechanism 17, to move the plunger 16. A
sensor, which is typically internal to the plunger driver mechanism
17, monitors fluid force as desired per system specifications. The
pump housing 14 may additionally include a display 19 and a
communications port 20. A typical display 19 may include operator
interface input mechanisms, such as a keyboard, touch screen
features, switches, a microphone, dials, and the like. The
communications port 20 may include a communications interface for
additional equipment, including laptops, handheld programming
devices and/or networking equipment. For instance, the
communications port 20 of the pump housing 14 may accommodate
RS-232 cabling.
[0029] While generally not shown in FIG. 1, one that is skilled in
the art will recognize that the exemplary system 10 may include
additional infusion lines, as well as valve mechanisms, clamps,
caps, stopcocks, connectors and additional sensors as per system
specifications.
[0030] The syringe 13 drives medication into the downstream
infusion line 22 at a controlled rate. The head of the plunger 16
is typically retained in such a way as to allow the plunger 16 to
be pushed in, but to prevent the plunger 16 from moving in of its
own accord as a result of siphoning of fluid from the syringe
barrel. For instance, the plunger 16 may be retained by means of
wedge-like arms that move across the forward surface of the head of
the plunger 16 and force the rear surface of the plunger head
against a forward facing surface of the plunger head retainer so as
to formally clamp it against the surface.
[0031] The display 19 may include options for a user to enter
input. Such input may include data pertaining to drug
concentration, patient weight, as well as desired doses and is dose
rates. The digital communication port 20 provides a mechanism for
external control, where desired. For instance, the pump housing 14
may be continuously cabled to a separate remote personal computing
device. One skilled in the art will appreciate that wireless
communications may be alternatively used. In any case, this
personal computing device can then run a particular program
tailored to provide the desired pattern of drug delivery
appropriate to the specific circumstance.
[0032] Regardless of the source of the input, the processor 31
contained within the pump housing 14 may initiate the volume and
fluid flow rates to be delivered to the patient. FIG. 2 illustrates
a hardware and software environment for a system 30 having such a
processor 31 configured to detect an occlusion. As discussed
herein, the processor 31 may monitor for an occlusion using input
from a sensor 33. A sensor, for purposes of this disclosure, may
include any device configured to detect a value indicative of
force. A suitable processor may include any device configured to
process an electronic signal.
[0033] The processor 31 of the system 30 typically couples to a
memory 32. As discussed herein, processor 31 may represent one or
more processors (e.g., microprocessors), and memory 32 may
represent the random access memory (RAM) devices comprising the
main storage of the system 30, as well as any supplemental levels
of memory, e.g., cache memory, non-volatile or backup memories
(e.g., programmable or flash memories), read-only memories, etc. In
addition, memory 32 may be considered to include memory storage
physically located elsewhere in the system 30, e.g., any cache
memory in a processor 31, as well as any storage capacity used as a
virtual memory, e.g., as stored within mass storage or on a
computer coupled to the system 30 via a network 38. As discussed
below in greater detail, stored data may include syringe type,
size, infusion rate and slope information, as well as force values.
The processor 31 may execute various computer software
applications, components, programs, objects, modules, etc. (e.g.,
rapid detection program 42, cancellation program 43, steady state
program 44, and bolus program 45, among others).
[0034] In general, the routines executed to implement the
embodiments of the invention, whether implemented as part of an
operating system or a specific application, component, program,
object, module or sequence of instructions will be referred to
herein as "programs." The programs typically comprise one or more
instructions that are resident at various times in the system 30.
When a program is read and executed by a processor 31, the program
causes the system 30 to execute steps or elements embodying the
various aspects of the invention.
[0035] Moreover, while the invention has and hereinafter will be
described in the context of a fully functioning system 30, those
skilled in the art will appreciate that the various embodiments of
the invention are capable of being distributed as a program product
in a variety of forms, and that the invention applies equally
regardless of the particular type of signal bearing media used to
actually carry out the distribution. Examples of signal bearing
media include, but are not limited to recordable type media such as
volatile and nonvolatile memory devices, floppy and other removable
disks, hard disk drives, optical disks (e.g., CD-ROM's, DVD's,
etc.), among others, and transmission type media such as digital
and analog communication links.
[0036] In addition, various programs described hereinafter may be
identified based on the application for which they are implemented
in a specific embodiment of the invention. However, it should be
appreciated that any particular program nomenclature that follows
is used merely for convenience, and thus the invention should not
be limited to use solely in any specific application identified
and/or implied by such nomenclature.
[0037] Those skilled in the art will recognize that the exemplary
environments illustrated in FIGS. 1 and 2 are not intended to limit
the present invention. Indeed those skilled in the art will
recognize that other alternative hardware and/or software
environments may be used without departing from the scope of the
invention.
[0038] FIG. 3 shows exemplary method steps suited for execution
within the hardware environments of FIGS. 1 and 2. More
particularly, the flowchart 200 of FIG. 3 includes steps for
automatically detecting an occlusion within a fluid line of a
medical infusion system during a pumping sequence. The system 10
initializes at block 202 of FIG. 3. The initialization step of
block 202 may include or be preceded by connecting a personal
computer to the communications port 20 of the housing 14. Thus, the
system 10 may include external processing devices configured to
connect to the port 20 as discussed herein.
[0039] The initialization of block 202 may include user specified
infusion protocols, operating parameters and other data. For
instance, the user may select one or more fluid is flow rates or
sequences may be selected based on a desired pattern of drug
delivery that is appropriate to the protocol of the patient.
Alternatively or additionally, certain parameters may be factory
set and/or automatically retrieved from memory or prior use. For
example, an earlier infusion protocol may be retrieved where an
infusion sequence is to be repeated for a patient.
[0040] Initialization may include recalling or defining an expected
relationship. This expected relationship may include an occlusion
slope. Such a slope may be predetermined using clinical data. For
instance, force measurements may be taken under known laboratory
conditions at the beginning and end of a window interval. These
force measurements are divided by the window to determine the
occlusion slope. Some such slopes may be stored in an associative
relationship with one or more of the known conditions as applicable
to a given pumping system scenario. For instance, a slope may be
stored in associative relationship with a particular type or size
of syringe, and/or a given infusion rate. As discussed in greater
detail in the text describing FIG. 6, the occlusion slope may be
determined as a function of a steady state slope detected in a
given patient application.
[0041] Where desired, system parameters can be set at block 202 to
tolerate "sticky" syringes and handle glitches in force caused by
various conditions, including a change in force due to
repositioning of the height of a pump, or the change in delivery
rate of another pump that is feeding the same delivery path.
[0042] Another setting accomplished at or prior to block 202 of
FIG. 3 may include specifying or recalling an appropriate window
size. The window size may define the interval(s) at which force
readings, or values, are to be accomplished. Put another way, a
window includes first and second force values communicated from the
force sensor 33 to the processor 31. As discussed herein, a
relationship between these force values is compared to an expected
relationship to determine the presence of an occlusion. That is,
the relationship is later compared to the expected relationship to
determine whether an occlusion should be declared.
[0043] Still another exemplary parameter that is set at or prior to
block 202 of FIG. 3 may include an occlusion detection time. The
occlusion detection time may define a minimum period of time
required to determine whether an occlusion has occurred. For
instance and as discussed in greater detail below, an occlusion
slope or other unexpected relationship may have to be sustained for
at least a period equal to the defined occlusion detection time
before an occlusion will be declared.
[0044] Block 202 of FIG. 3 may be additionally include initiating
an infusion at a specified infusion rate. For instance, a medicated
fluid may begin to flow at block 202 at an infusion rate of 5
ml/hr.
[0045] At block 204 of FIG. 3, the system 10 obtains or otherwise
determines a first force value. This first force value may be
obtained at a time, T1, for instance. As discussed herein, time T1
may be stipulated by parameters input at or prior to block 202.
While a suitable force value may comprise any measurement
indicative of force present within the system 10, a typical force
value includes a binary output from a transducer in communication
with the force sensor. Such a transducer may comprise an
analog-to-digital converter, for instance. As such, an electronic
signal from the force sensor is processed by the transducer to
generate an output. The output from the A/D converter thus varies
according to the force detected by the force sensor. For example, a
force reading of two PSI may cause the A/D converter to output a
binary value of 76 mV. This voltage output may later be converted
to a "count" unit for processing considerations. Either or both the
output and count comprise force values for purposes of this
specification and may be stored at block 205 for later use.
[0046] A subsequent, second force value may be obtained at block
206. This second force value may be accomplished in a fashion
similar to that of block 204 at time, T2. As before, time T2 may be
predetermined as part of an infusion application setup. Where
desired, this second force value is stored also at block 205. While
steps for determining only two force values are shown at blocks 204
and 206, one of skill in the art will appreciate that additional
force value measurements may be taken in accordance with the
principles of the present invention. That is, more than two force
values may be used to determine a relationship that is compared to
the expected relationship.
[0047] The system 10 at block 207 of FIG. 3 uses the force values
obtained at blocks 204 and 206 to determine a relationship between
them. For instance, the system 10 may determine a slope at block
207. More particularly, the difference between the obtained is
force values may be divided by the difference in the times that the
respective force values were obtained. One or more force values may
be stored at block 205 for later use.
[0048] Prior to proceeding to another step associated with
detecting an occlusion, the system 10 at block 208 may determine if
steady state has been achieved. While discussed more particularly
in connection with FIG. 6, steady state includes a status of the
system 10 at which initial conditions of an infusion application
will generally have less impact on occlusion determination
processes. One such exemplary initial condition may include an
amplified force reading attributable to the normal and relatively
sudden influx of fluid into a tube 22 at the onset of an infusion
application. A determination of steady state may thus include, for
instance, verification that a pump has been primed and/or that a
time or fluid volume limit has been exceeded. This step of block
208 reduces the possibility of initial conditions triggering a
false occlusion.
[0049] The occlusion slope specified at block 202 of FIG. 3 is
retrieved at block 209 by the system 10. Such an occlusion slope
may comprise the expected relationship as discussed herein. At
block 210 of FIG. 3, the retrieved occlusion slope is compared to
the trial slope determined at block 207. More particularly, if the
determined slope is less than the occlusion slope retrieved at
block 209, then the system 10 may not declare an occlusion and may
merely continue to monitor for an occlusion. For instance, the
system 10 may shift the detection window and obtain additional
force values at blocks 218, 204, and/or 206 to determine a new
trial slope at block 207. One embodiment that is consistent with
the principles of the present invention may additionally reset
clock or other counter tracking time at block 211.
[0050] Should the detected or other trial slope alternatively be
greater than or equal to the retrieved occlusion slope/expected
relationship at block 210, the system 10 may determine at block 211
if an occlusion has been canceled. While discussed in greater
detail below as the subject of FIG. 7, such a cancellation may
occur where, for instance, an occlusion cancellation slope is
determined subsequent to the slope determination of block 207.
Cancellation of an occlusion may result in the reset at block 213
of a clock or other counter tracking the passage of time associated
with an occlusion detection application. Such a count may be useful
for determining when an occlusion detection time has been
reached.
[0051] More particularly, where no cancellation has occurred at
block 211, it may be determined at block 212 whether a period
corresponding to the occlusion detection time has expired. As
discussed herein, the occlusion detection time may be defined as a
minimum duration in which an occlusion slope must be sustained in
order to declare an occlusion. Step 212 is accomplished, in part,
to mitigate occurrences of false occlusions. Namely, an alarm is
not generated at block 217 until the occlusion time has expired at
block 212. The application counter continues to increment at block
216 until the occlusion time is reached or some other condition
intervenes.
[0052] Where the detected slope is greater than or equal to the
occlusion slope, and the occlusion detection time has lapsed at
block 212, the system 10 will generate an occlusion alarm at block
217. While a typical alarm may include an audible signal and/or a
flashing display 19, a suitable alarm may comprise any indicator
configured to communicate an occlusion status to a user.
[0053] As with all of the flowcharts disclosed in this
specification, one of skill in the art will appreciate that any of
the exemplary steps 202-218 of the flowchart 200 of FIG. 3 may be
omitted, rearranged, and/or augmented with additional steps in
accordance with the principles of the present invention. Moreover,
one of skill in the art will appreciate that the functions of these
steps 202-218 of the flowchart 200 may be realized in software
and/or hardware environments different than those described in
connection with FIGS. 1 and 2.
[0054] FIG. 4 shows a graph 300 that plots force along its y-axis
302 against time along its x-axis 304. The resultant, plotted line
306 reveals a slope that is indicative of the pressure, or force,
within the system 10 as a function of time. For purposes of this
specification, "force" and "pressure" may be used interchangeably.
In the above-discussed embodiment, the slope of the line 306 may be
compared to an expected slope to determine if an occlusion alarm
should be initiated. In one sense, an embodiment of the present
invention capitalizes on the fact that the slope experienced by a
system 10 in occlusion may exhibit steady and predictable
characteristics.
[0055] As shown in FIG. 4, force measurements are accomplished at
windows 310-316. A window for purposes of this specification may
comprise two or more time measurements, to include multiple smaller
window increments and measurements. More particularly, window 310
may begin at time T2 and ends at time T2. Window 312
correspondingly picks up at time T2 and ends at time T3. While
advantageous in certain applications, one of skill in the art
should appreciate that such windows need not be consecutive and may
be accomplished at any preset and/or random interval. For example,
a suitable window may additionally comprise a period between T2 and
T.sub.L-1. In any case, the system 10 may buffer or otherwise store
multiple force values 308 in a window buffer.
[0056] The size of each window 310-316 may be adjusted to meet any
number of system requirements. For instance, the size, or time
spanning a window 310 may be adjusted to eliminate or otherwise
account for fractions of counts. For example, the size of a first
window 310 may be adjusted such that its size will generally detect
all of the count data occurring between T1 and T2. Such precaution
may avoid instances where the transducer outputs, for example, a
sixth count at the border of window 312, where most of the force
associated with the sixth count was actually generated in the time
span of window 310. As such, the window size may be expanded or
contracted to avoid fractional readouts. Continuing with the above
example, the size of the windows 308 may be expanded such that the
sixth count registers in window 310. In any case, other processing
and conversionary applications as appreciated by one skilled in the
art may be employed to achieve desired readouts, irrespective of
window size.
[0057] As discussed herein, each force value may comprise a count
from the transducer/analog-to-digital converter over a time span
defined by the window size, T1-T2. For instance, a window having a
time span of one minute may generate 76 counts. Thus, the counts
are indicative of force within the system 10, and may be used along
the y-axis 302 of FIG. 4 for use in plotting against time 304. The
resultant slope may comprise a relationship that is later compared
to an expected relationship to determine the presence or absence of
an occlusion.
[0058] FIG. 5 shows an exemplary database structure 380 that has
application with embodiments of the present invention. For
instance, the structure 380 may comprise a lookup table accessible
to programs 42-45 that are consistent with the present invention.
Such a lookup table may include fields for syringe size 382,
infusion rate 384 and slope rate 386 data, among other criteria.
For instance, other suitable criteria may include the nature of the
substance being infused, the concentration or dissolution of the
substance in is the fluid, fluid viscosity; the recipient,
including sex, age and physical attributes, the occurrence of
change in measurable diagnostics related to the actions or effects
of the substance being infused, drug concentration predictability,
as well as local practices, policies, protocols and regulations or
other considerations, including operator judgment. Indeed, one of
skill in the art should recognize that any criteria relating to an
infusion process may be additionally or alternatively included
within or affect the contents of a memory structure that is
consistent with the underlying principles of the present
invention.
[0059] An embodiment of the present invention processes the data
contained within the database fields 382 and 384 as input by the
user to determine an expected relationship, or slope rate 386. This
slope rate 386, which may comprise and/or be converted to counts
per minute, may be recalled from memory 32 at block 209 of FIG. 3,
for example.
[0060] FIG. 6 shows exemplary method steps suited for determining
if steady state has been achieved. At the onset of an infusion
process, an initial slope is generated that approaches or exceeds
an occlusion slope. This elevated force level may be caused by the
tubing 22 and other components of the system 10 reacting to a
sudden influx, or ramping up, of pumped fluid. That is, some time
is required by the system 10 in order to adjust and achieve a
relaxed flow of fluid toward the patient 24. Given time,
pressure/force within the system 10 eventually and relatively
relaxes in the absence of an occlusion. That is, the force levels
off to a more moderate slope. This period of leveling generally
coincides with the system 10 achieving steady state.
[0061] The processes of the flowchart 400 of FIG. 6 accommodate the
initial influx of fluid into the system 10, while mitigating false
occurrences of occlusion alarms. The system 10 generally uses the
steady state detection processes shown in FIG. 6 to determine when
steady state has been achieved. For instance, when a slope
generated as a product of the actual force over time is below or
equal to an expected occlusion or steady state detection slope.
Some embodiments may require the detected slope to last over some
minimum occlusion time before declaring steady state or an
occlusion. The same or another embodiment of a system 10 that is
consistent with the present invention may declare steady state upon
the expiration of some designated startup time or in response to an
infused volume level.
[0062] Steady state detection is enabled at block 402.
Initialization processes at block 402 may include user and/or
factory specified parameters, such as a minimum time for occlusion,
a startup time, steady state slope and a startup volume.
[0063] The system 10 determines or otherwise obtains force values
at block 404. As discussed herein, an exemplary force value may
comprise a count output from an analog-to-digital converter in
communication with a force sensor. The force value may be detected
by a force or pressure sensor in communication with the downstream
infusion tube 22, for instance.
[0064] The system 10 may determine whether the pump system 10 is
primed at block 406. Priming the pump may include the user pushing
a button on a display 19 that initializes the steady state
detection processes, along with elevating pressure within the
system 10 to an acceptable level. Should the pump not be primed as
such at block 406, the steady state detection algorithm 44 may
declare steady state where the volume of fluid that has been
delivered is greater than a startup volume. The volume delivered
and/or the startup volume may be determined as a function of time
and the infusion rate. Where such a condition at block 424 is
determined to exist, then steady state may be declared at block
418. Otherwise, additional force values may be obtained at block
404. As discussed herein, such force values may be numerous as per
system specifications and conditions.
[0065] The system 10 may determine a trial slope at block 410 using
the force values obtained at block 404. This determined, actual, or
trial slope may be compared to a slope retrieved from memory 32.
While the retrieved slope may comprise the occlusion slope in one
embodiment, another may retrieve a steady state slope having some
other appropriate value.
[0066] Should the slope determined at block 410 be greater than or
equal to the retrieved slope as determined at block 412, then the
system 10 may determine at block 416 if a steady state startup time
has been exceeded. The steady state startup time may comprise a
time period after which steady state will be declared at block 416.
This specified startup time limit includes a time at which elevated
startup slopes associated with a pre-steady state timeframe
normally level off. That is, the startup time may comprise some
preset period in which normal (non-occlusion), pre-steady state
conditions should have resolved is themselves. Where such a startup
time limit has been met or exceeded at block 416, the system may
declare steady state at block 418. Otherwise at block 416, the
system 10 may continue to determine force values at block 404 until
the startup time limit or another condition has been met.
[0067] Should the slope determined at block 410 fail to meet or
exceed the occlusion slope at block 412, the system may rely on
time-based analysis at block 422 to determine if some specified
startup time limit has expired. Where such a startup time limit has
been met or exceeded at block 416, the system may declare steady
state at block 418.
[0068] Once steady state has been detected, the system 10 may
progress into another aspect of occlusion detection as discussed
herein. Upon exiting steady state at block 426, for example, the
determined slope will then be compared to the same or another
(non-steady state) occlusion slope to determine if an occlusion is
present within the system 10.
[0069] Flowchart 488 of FIG. 7 outlines exemplary process steps
489-498 that further expound upon the occlusion cancellation step
215 of FIG. 3. That is, the method steps shown in FIG. 7 function
to cancel an occlusion alarm and help mitigate incidences of false
occlusions. At block 489 of FIG. 7 the system 10 obtains force
samples. These force samples include force values as discussed
above and may be retrieved from memory or a force sensor. As
throughout this specification, multiple force samples may be used
to determine the presence or absence of an occlusion.
[0070] A trial slope or other relationship is determined at block
490 of FIG. 7. The slope may reflect force values over time as
shown and discussed above in connection with FIG. 4.
[0071] At block 491, an occlusion cancellation slope value may be
retrieved. The occlusion cancellation slope may be predetermined
and specified by a user in a manner similar to the occlusion slope
discussed in connection with FIG. 3. That is, the occlusion
cancellation slope may account for such factors as syringe size,
type and the rate of infusion, among other factors. The occlusion
cancellation slope is typically smaller than or equal to the
occlusion slope. That is, detection of the occlusion cancellation
slope represents a departure from the relatively steeper slope
associated with an occlusion, e.g., a lessening of force within the
system 10.
[0072] The system 10 may compare at block 492 the slope determined
at block 490 of FIG. 7 with the occlusion cancellation slope
retrieved at block 491. More particularly, the system 10 may
determine if the trial slope is greater than or equal to the
cancellation occlusion slope. If this condition is satisfied at
block 492, then the system may increment a register a block 493. A
register for purposes of this specification may include any count
and be realized in either a software and/or a hardware
environment.
[0073] Alternatively, should the determined slope be less than the
occlusion cancellation slope as determined at block 492 of FIG. 7,
the register is not incremented at block 494. In another or the
same embodiment, the register may be reset at block 494 in response
to the occlusion cancellation slope being greater than the
determined slope.
[0074] The register may be compared to a threshold value at block
496 at the expiration of an occlusion cancellation time. The
threshold value and occlusion cancellation times may be preset by a
user. As with all settings discussed herein, these settings may be
modified in the field by users to reflect preferences. In the
exemplary step of block 496 of FIG. 7, where the register is
greater than or equal to the threshold value, the system 10 may
proceed with an occlusion alarm at block 497. Alternatively at
block 498, the occlusion alarm may be canceled in response to the
threshold value equaling or being greater than the current value
contained within the register. Such condition may arise, for
instance, where a temporary increase in force has resulted from a
corresponding change in the elevation of a patient, not an
occlusion.
[0075] The flowchart 500 of FIG. 8 shows additional processes
configured to detect an occlusion within an infusion system 10. The
exemplary process steps are particularly suited for application
within the context of a bolus injection. Bolus injections present
unique challenges with regard to occlusion detection, since the
high volumes and infusion rates associated with bolus injections
are conventionally difficult to discern from occluded
conditions.
[0076] The user may initialize the system 10 at block 502 of FIG.
8. Initialization processes may include setting a bolus occlusion
limit. As discussed below, a bolus occlusion limit may be a value
that functions as a gauge for activating features of the occlusion
detection processes of the present invention. Other settings
accomplished at block 502 may include setting a delay time as
discussed below. The initialization is processes of block 502 may
presume that a user has connected a personal computer or other
processing device to a pump. Such a scenario may be appropriate
where desired interface hardware is not included within the pump
housing, for instance. Initialization at block 502 may also include
commencing infusion of medication. For example, a user may instruct
the system 10 to pump fluid at a rate of 600 ml/hr for a given
bolus injection.
[0077] The system 10 obtains a force value at block 504. The force
value may comprise a count output from an analog-to-digital
converter. For instance, the system 10 may register 112 counts
within the time span of one minute. However, one skilled in the art
will appreciate that any value indicative of force within the
system 10 may be alternatively used.
[0078] The system 10 determines if the obtained force value is
greater than the occlusion limit at block 506. The occlusion limit
may be set at any value. Where the obtained force value is less
than the occlusion limit, then the system may continue to monitor
force readings at block 504.
[0079] In the flowchart 500 of FIG. 8, the processor 31 of the
system 10 may pause, interrupt, decrease, stop or otherwise alter
travel of the plunger 16 (and delivery of the fluid) at block 508
in response to determining that the force value obtained at block
504 is greater than the occlusion limit, or expected value, as
defined at block 502. One of skill in the art will appreciate that
while complete halting of the plunger 16 at block 508 is desired in
most cases, another embodiment consistent with the invention may
merely slow, reduce or otherwise alter delivery at block 508.
[0080] The system 10 may verify that it is operating in bolus
delivery mode at block 510. This step at block 510 allows the bolus
infusion processes to work within the context of normal, non-bolus
infusions. More particularly, if the system determines at block 510
that a bolus is not being delivered, then an occlusion alarm may be
generated at block 512. As with other embodiments of the present
invention, detection of an occlusion at block 512 may initiate
remedial action. Such action may include verifying the function of
the system 10, as well as adjusting flow rate and other infusion
parameters to compensate for a potential occlusion.
[0081] If, however, the user has indicated at block 502 that a
bolus is being delivered, is then a clock or other counter is
monitored at block 514. More particularly, the processor 31 may
determine at block 514 whether a span of time from when delivery
was stopped at block 508 now exceeds or equals a period specified
at block 502 as the set delay time limit. This delay time limit may
be set to a duration that will allow the force within most systems
to decrease below the occlusion limit in the absence of an
occlusion. In the embodiment of FIG. 8, additional force values are
obtained at block 504 prior to the clock delay time limit being
reached at block 514.
[0082] Continuing with FIG. 8, the system 10 determines at block
516 if the current force value is less than the occlusion limit. As
above, the occlusion limit value may be retrieved from memory 32
prior to or at step 516. If the current force in the system remains
greater than the occlusion limit at block 516, then an occlusion
alarm may be generated at block 512. Otherwise, the bolus infusion
is resumed at block 520. That is, travel of the plunger 16 resumes
and fluid delivery resumes at its former or a different rate.
[0083] As suggested by block 518 of FIG. 8, embodiments of the
present invention may resume the bolus at a reduced rate. As such,
it should be appreciated by one with skill in the art that other
embodiments may resume a bolus infusion at block 520 at the prior
or any other infusion rate.
[0084] Allowing the force in the system 10 to relax for a period
equal to the delay time limit, in combination with the reduced rate
feature of block 518, enables a bolus infusion in a manner that
does not exceed the occlusion limit and/or initiate a false
occlusion alarm. That is, the switch-on and switch-off bolus
features of blocks 508-520 of FIG. 8 reduce incidences of false
occlusion, while enabling bolus applications at maximum infusion
rates. In any case, the occlusion detection processes end at block
522.
[0085] One of skill in the art will appreciate that the sequence of
the steps in all of the included flowcharts may be altered, to
include omitted processes without conflicting with the principles
of the present invention. Similarly, related or known processes can
be incorporated to complement those discussed herein. It should be
further understood that any of the embodiments and associated
programs discussed above are compatible with most known infusion
processes and may be fully optimized to realize even greater
efficiencies.
[0086] While the present invention has been illustrated by the
description of embodiments thereof, and while the embodiments have
been described in considerable detail, it is not intended to
restrict or in any way limit the scope of the appended claims to
such detail. Additional advantages and modifications will readily
appear to those skilled in the art. For example, while this
specification focused generally on a syringe pump, one skilled in
the art will recognize that the underlying principles of the
present invention apply equally to other medical pumping systems,
to include cassette based and peristaltic pumps. Additionally,
while force transducers are discussed above in connection with
several embodiments, pressure transducers may have equal or greater
applicability in other others that are consistent with the
principles of the present invention. For instance, a sensor
comprising a pressure transducer may be used at the outlet of a
syringe or in the tubing.
[0087] Moreover, while embodiments discussed herein generally
relate to downstream occlusion, they may apply equally to upstream
occlusion detection. As such, a fluid source may comprise a
syringe, as well as a bag located upstream. Furthermore, one of
skill in the art will appreciate that all slope, time and other
value comparisons used to determine the presence of an inclusion
may be configured such that either a higher or lower value will
trigger a given process. For instance, an alarm of one embodiment
may be initiated in response to a determined slope being lower or
higher than an expected slope, depending on how the system 10 is
configured.
[0088] Additionally, while slope determinations serve well for
relational comparisons, a suitable expected relationship may
alternatively comprise any value indicative of force within the
system. In one embodiment, a suitable expected relationship may be
a product of both slope and window size. As such, the system 10 may
maintain a number of force sensor readings in a buffer or other
memory 32. A difference in force sensor readings may be compared to
the product of the slope and window size to determine if an
inequality or other relationship exists. For example, if the
difference in force values is greater than or equal to the product
of the slope and window size, then a detection count may be
incremented by one. Otherwise, the detection count register may
remain unchanged or be reset to zero. When the increment detection
count register contents are greater than or equal to those of
another occlusion detection counter, an occlusion is is
declared.
[0089] Moreover, one of skill in the art will appreciate that while
the processes of the present invention may achieve occlusion
detection with only a single force sensor, embodiments that are
consistent with the principles of the present invention may include
multiple force sensors and sensor positions. The invention in its
broader aspects is, therefore, not limited to the specific details,
representative apparatus and method, and illustrative examples
shown and described. Accordingly, departures may be made from such
details without departing from the spirit or scope of the general
inventive concept.
* * * * *