U.S. patent application number 16/895910 was filed with the patent office on 2020-09-24 for methods & systems to determine multi-parameter managed alarm hierarchy during patient monitoring.
The applicant listed for this patent is Spacelabs Healthcare L.L.C.. Invention is credited to William Gregory Downs, Jeffrey Jay Gilham.
Application Number | 20200303067 16/895910 |
Document ID | / |
Family ID | 1000004874114 |
Filed Date | 2020-09-24 |
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United States Patent
Application |
20200303067 |
Kind Code |
A1 |
Gilham; Jeffrey Jay ; et
al. |
September 24, 2020 |
Methods & Systems to Determine Multi-Parameter Managed Alarm
Hierarchy During Patient Monitoring
Abstract
The present specification discloses systems and methods of
patient monitoring in which multiple sensors are used to detect
physiological parameters and the data from those sensors are
correlated to determine if an alarm should, or should not, be
issued, thereby resulting in more precise alarms and fewer false
alarms. Electrocardiogram readings can be combined with invasive
blood pressure, non-invasive blood pressure, and/or pulse oximetry
measurements to provide a more accurate picture of pulse activity
and patient respiration. In addition, the monitoring system can
also use an accelerometer or heart valve auscultation to further
improve accuracy.
Inventors: |
Gilham; Jeffrey Jay;
(Sammamish, WA) ; Downs; William Gregory;
(Snoqualmie, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Spacelabs Healthcare L.L.C. |
Snoqualmie |
WA |
US |
|
|
Family ID: |
1000004874114 |
Appl. No.: |
16/895910 |
Filed: |
June 8, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15463250 |
Mar 20, 2017 |
10699811 |
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16895910 |
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13045539 |
Mar 11, 2011 |
9629566 |
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15463250 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/0205 20130101;
G16H 40/63 20180101; G08B 25/016 20130101; A61B 5/0836 20130101;
A61B 5/14542 20130101; A61B 5/1135 20130101; A61B 5/0468 20130101;
A61B 5/7246 20130101; A61B 5/021 20130101; A61B 5/02 20130101; A61B
5/02455 20130101; A61B 5/0402 20130101 |
International
Class: |
G16H 40/63 20060101
G16H040/63; A61B 5/00 20060101 A61B005/00; A61B 5/0205 20060101
A61B005/0205; A61B 5/021 20060101 A61B005/021; A61B 5/0245 20060101
A61B005/0245; A61B 5/0468 20060101 A61B005/0468; A61B 5/113
20060101 A61B005/113; A61B 5/145 20060101 A61B005/145; A61B 5/0402
20060101 A61B005/0402; A61B 5/02 20060101 A61B005/02; G08B 25/01
20060101 G08B025/01 |
Claims
1. A non-transitory computer readable medium configured to store a
plurality of programmatic instructions for processing data
indicative of physiological parameters comprising: code for
receiving accelerometer data generated by an accelerometer device;
code for analyzing the accelerometer data over a period of time,
wherein the accelerometer data over the period of time is
indicative of at least one of a number of steps taken by a wearer
of the accelerometer device or a rate of the steps, and wherein the
analyzed accelerometer data is indicative of a motion of the
wearer; code for receiving physiological data generated by at least
one physiological sensor used to monitor the wearer, wherein the
physiological data has a time of occurrence associated therewith
and wherein the physiological data comprises electrocardiogram
(ECG) data and data indicative of the wearer's pulse signal; code
for correlating the analyzed accelerometer data with the time of
occurrence of the ECG data to determine a degree of correlation;
code for causing an alarm to issue if the ECG data, which are
correlated with the accelerometer data is indicative of an abnormal
physiological condition, and, code for suppressing said alarm,
which is based upon the ECG data, if the accelerometer data
correlated with the ECG data is indicative of a regular motion of
the wearer.
2. The non-transitory computer readable medium of claim 1 wherein
said plurality of programmatic instructions further comprises code
for comparing said degree of correlation between the analyzed
accelerometer data and the time of occurrence of the physiological
data to a predetermined value.
3. The non-transitory computer readable medium of claim 1 wherein
said code for correlating determines if an abnormal feature in the
analyzed accelerometer data is correlated in time with the abnormal
physiological condition.
4. The non-transitory computer readable medium of claim 1 wherein
said degree of correlation is dependent upon at least one of the
number of steps, the rate of steps, an amplitude of a physiological
signal indicative of the physiological data, a duration of the
physiological signal, or a noise level within the physiological
data.
5. The non-transitory computer readable medium of claim 1 wherein
the at least one physiological sensor comprises an ECG
electrode.
6. The non-transitory computer readable medium of claim 1 further
comprising code for modifying a sensitivity of an alarm, wherein
said code comprises code for reducing the sensitivity of the alarm
if the analyzed accelerometer data is indicative of the regular
motion of the wearer.
7. The non-transitory computer readable medium of claim 1 further
comprising code for varying a correlation of the physiological data
generated by the at least one physiological sensor.
8. The non-transitory computer readable medium of claim 1 further
comprising code for suspending an operation of the at least one
physiological sensor if the analyzed accelerometer data is
indicative of the motion of the wearer.
9. The non-transitory computer readable medium of claim 1 further
comprising code for analyzing the motion of the wearer using the
analyzed accelerometer data to determine if the wearer is engaged
in an activity causing an increase in the wearer's respiration rate
and causing the alarm to issue based, at least in part, on said
analysis.
10. The non-transitory computer readable medium of claim 1 wherein
the accelerometer device is a tri-axial accelerometer.
11. The non-transitory computer readable medium of claim 1 further
comprising code for causing the alarm to issue if the accelerometer
data is indicative of cessation of all regular motion of the wearer
or if the physiological data is unavailable.
12. The non-transitory computer readable medium of claim 1 further
comprising code for analyzing the accelerometer data to determine a
posture of the wearer and for recording changes in the posture.
13. The non-transitory computer readable medium of claim 1 further
comprising code for analyzing the accelerometer data to determine a
posture of the wearer and for recording changes in the posture in
relation to data obtained from the at least one physiological
sensor, wherein the at least one physiological sensor comprises an
ECG electrode.
14. The non-transitory computer readable medium of claim 13 further
comprising code for determining a number of posture changes per
hour and correlating the determined number with the accelerometer
data to obtain an overall activity state of the wearer and code for
causing a notification to issue if the overall activity state of
the wearer does not lie with a predefined range.
15. The non-transitory computer readable medium of claim 1 further
comprising code for detecting motion artifact induced signal
changes in the physiological data using the accelerometer data.
16. The non-transitory computer readable medium of claim 1 wherein
said plurality of programmatic instructions further comprises code
for suppressing an alarm associated with a non-invasive blood
pressure reading if the accelerometer data is indicative of
physical activity greater than a threshold value.
17. The non-transitory computer readable medium of claim 1 further
comprising code for suppressing an alarm by correlating the
accelerometer data with one or more ECG waveforms.
18. The non-transitory computer readable medium of claim 1 wherein
the physiological data comprises ECG data and comprises data
indicative of the wearer's blood pressure (BP) waveform.
19. The non-transitory computer readable medium of claim 18 further
comprising: code for decreasing a priority level of the alarm if
the ECG data is indicative of ventricular tachycardia and the BP
waveform is indicative of a continuing pulse with a regular rhythm
and amplitude; and code for increasing a priority level of the
alarm if the ECG data is indicative of lack of cardiac activity and
the BP waveform is indicative of a cessation of pulsatile activity
of the wearer.
20. The non-transitory computer readable medium of claim 18 further
comprising : code for decreasing a priority level of the alarm if
the ECG data is unavailable and the BP waveform is indicative of a
continuing pulse with a regular rhythm and amplitude.
Description
CROSS-REFERENCE
[0001] The present application is a division application of U.S.
patent application Ser. No. 15/463,250, entitled "Methods &
Systems to Determine Multi-Parameter Managed Alarm Hierarchy During
Patient Monitoring" and filed on Mar. 20, 2017, which is a
continuation application of U.S. patent application Ser. No.
13/045,539, of the same title, filed on Mar. 11, 2011, and issued
as U.S. Pat. No. 9,629,566 on Apr. 25, 2017, both of which are
incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present specification invention relates to patient
monitoring systems. In particular, the specification discloses
systems and methods for analyzing a plurality of physiological
parameters to promote, demote, or suppress alarm conditions.
BACKGROUND OF THE INVENTION
[0003] Most patient monitoring is typically implemented by
measuring and observing a plurality of physiological parameters
such as: ECG (Electrocardiogram), Pulse Oximetry (involving
measuring blood oxygen levels or SpO.sub.2), Respiration (derived
from ECG signal or from other parameters), Invasive Blood Pressure
(or IBP that involves direct measurement of blood pressure from an
indwelling catheter), and Non-Invasive Blood Pressure (or NIBP that
involves use of automated oscillometric methods).
[0004] Typically these physiological parameters have a set of vital
signs and derived measurements which can be configured to alert a
caregiver if the measured values move outside of configured ranges.
Each parameter has a plurality of alarms that can be considered to
be of different priorities. However, prior art methods and systems
tend to treat each of these parameters independently for
deciding/determining alarm situations or fail to provide a workable
mechanism for effectively determining whether an alarm state,
derived from the signal of a particular patient monitoring device,
is false, likely to be false, or sufficiently indicative of the
state of a patient to warrant alerting a caregiver. As a result,
the clinical user may experience an unacceptable number of alarms
within these patient monitoring systems. The caregiver will
ultimately see a conglomeration of alarm states from various
fluctuations for each of the parameters, leading to unnecessary
distraction and caregiver apathy regarding alarms.
[0005] Accordingly there is need in the art for methods and systems
that effectively suppress or demote the number of false alarms the
user sees and to make sure that when the system alarms there is a
significant probability that the patient requires immediate
attention.
SUMMARY OF THE INVENTION
[0006] In one embodiment, the present specification discloses a
computer readable medium storing a plurality of programmatic
instructions for processing data indicative of physiological
parameters comprising: a) code for receiving ECG data generated at
least in part by an ECG device, wherein said ECG data comprises a
plurality of features and wherein at least one of said features has
a designation associated therewith and a time of occurrence
associated therewith; b) code for receiving pulse data indicative
of a patient's pulse response, wherein said pulse data is obtained
from at least one sensor separate from said ECG device and wherein
said pulse data has a designation associated therewith and a time
of occurrence associated therewith; c) code for correlating the
designation and time of said at least one feature of the ECG data
with the designation and time of the pulse data to determine a
degree of correlation; and d) code for causing an alarm to issue,
wherein the alarm is only issued if said degree of correlation
indicates the patient has an abnormal heart condition.
[0007] Optionally, the plurality of programmatic instructions
further comprises code for comparing said degree of correlation to
a predetermined value. The code for causing an alarm to issue only
causes the alarm to issue if said comparison indicates the patient
has an abnormal heart condition. The designation of at least one
feature of the ECG data is either normal or abnormal. The
designation of the pulse data is either normal or abnormal. The
correlation functions to determine if an abnormal feature in the
ECG data is correlated in time with an abnormal pulse. If the
correlation determines an abnormal feature in the ECG data is
correlated in time with an abnormal pulse, an alarm indicative of
an abnormal heart condition is issued. If not, an alarm is not
issued or, if generated by another source, is actively suppressed.
The correlation is further dependent upon at least one of an
amplitude of an ECG signal, amplitude of a pulse signal, duration
of a pulse signal, noise level within said ECG data, or noise level
within said pulse data. The at least one sensor is an invasive
blood pressure (IBP) monitoring device, a non-invasive blood
pressure (NIBP) monitoring device, heart valve sounds monitoring
device, or pulse oximetry (SpO.sub.2) monitoring device. The
plurality of instructions further comprises code for causing at
least one sensor to initiate a collection of pulse data based on
said ECG data. The code causes a non-invasive blood pressure
monitoring device to inflate a cuff and collect pulse data when
said ECG data is representative of a heart rhythm indicative of
atrial fibrillation. The plurality of instructions further
comprises code to cause a non-invasive blood pressure monitoring
device to inflate a cuff and collect pulse data based upon said
correlation.
[0008] In another embodiment, a computer readable medium storing a
plurality of programmatic instructions for processing data
indicative of physiological parameters comprising: a) code for
receiving bio-impedance data generated at least in part by a
respiration monitoring device, wherein said bio-impedance data
comprises a plurality of features and wherein at least one of said
features has a designation associated therewith and a time of
occurrence associated therewith; b) code for receiving respiration
data indicative of a patient's respiration, wherein said
respiration data is obtained from at least one sensor separate from
said respiration monitoring device and wherein said respiration
data has a designation associated therewith and a time of
occurrence associated therewith; c) code for correlating the
designation and time of said at least one feature of the ECG data
with the designation and time of the respiration data to determine
a degree of correlation; and d) code for causing an alarm to issue,
wherein the alarm is only issued if said degree of correlation
indicates the patient has abnormal respiration.
[0009] Optionally, the respiration monitoring device is at least
one of a capnography device, pneumatic respiration transducer
device, strain gauge or stretch gauge. The sensor is at least one
of an ECG device, invasive blood pressure (IBP) monitoring device,
pulse oximetry (SpO.sub.2) monitoring device, or motion detecting
device. The motion detecting device is an accelerometer. The motion
detecting device is an accelerometer integrated with an ECG
electrode. The designation of at least one feature of the
bio-impedance data is either normal or abnormal. The designation of
the respiration data is either normal or abnormal. The correlation
functions to determine if an abnormal feature in the bio-impedance
data is correlated in time with abnormal respiration data. If said
correlation determines an abnormal feature in the bio-impedance
data is correlated in time with abnormal respiration data, an alarm
indicative of an respiration condition is issued. The respiration
condition is a sleep apnea event. The plurality of instructions
further comprises code to receive motion data from said
accelerometer and determine whether a patient has fallen. The
plurality of instructions further comprises code to receive motion
data from said accelerometer, to determine whether a patient is
engaged in an activity which would increase the patient's
respiration rate, and to cause said alarm to issue or not issue
based, at least in part, on said determination. The plurality of
instructions further comprises code to receive motion data from
said accelerometer, to receive ECG data, to determine whether
variations in ST segments of said ECG data are caused by patient
activity, and to cause said alarm to issue or not issue based, at
least in part, on said determination.
[0010] It should be appreciated that the plurality of instructions
described herein are stored in a memory structure, such as a hard
disk, ROM, RAM, or any other type of memory device, and executed by
at least one processor. The instructions may be co-located with the
sensors or monitors or may be remote therefrom. They may be
integrated into a separate controller or computer that is in data
communication with the sensors, or operated as a software module
integrated into one or more of the sensing devices themselves.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other features and advantages of the present
invention will be appreciated, as they become better understood by
reference to the following detailed description when considered in
connection with the accompanying drawings, wherein:
[0012] FIG. 1 shows a flow diagram depicting a method of using a
plurality of parameters to determine an alarm hierarchy;
[0013] FIG. 2a is a graphical representation of an ECG (III) signal
with waveform noise and a corresponding IBP (ART) signal showing
normal cardiac activity for the same interval;
[0014] FIG. 2b is a graphical representation of an ECG (III) signal
with waveform noise and a corresponding IBP (ART) signal showing
lack of cardiac activity for the same interval;
[0015] FIG. 3a is a graphical representation showing
plethysmograph-assisted analysis for atrial ectopic beats;
[0016] FIG. 3b is a graphical representation of ECG (V1), ECG2 (II)
and SpO.sub.2 signals at time T.sub.0 for plethysmograph-assisted
ventricular beat analysis;
[0017] FIG. 3c is a graphical representation of ECG (V1), ECG2 (II)
and SpO.sub.2 signals at time T.sub.1 for plethysmograph-assisted
ECG signal noise analysis;
[0018] FIG. 4 is a graphical representation of invasive pressure
systolic peak modulation with respiration signals;
[0019] FIG. 5a is an illustration of one embodiment of a disposable
ECG electrode;
[0020] FIG. 5b is an illustration of the disposable ECG electrode
shown in FIG. 4a, further showing a reusable snap electrode
wire;
[0021] FIG. 5c is an illustration of the reusable snap electrode
wire shown in FIG. 4b, attached to the ECG electrode and with an
integrated accelerometer;
[0022] FIG. 6 is a graphical representation of chest wall movement
in a patient wearing an accelerometer while supine;
[0023] FIG. 7 is a graphical representation of chest wall movement
in the same patient wearing an accelerometer after standing up;
and
[0024] FIG. 8 is a graphical representation of chest wall movement
in the same patient wearing an accelerometer while walking.
DETAILED DESCRIPTION
[0025] In one embodiment, the present specification discloses a
system and method for collectively analyzing a plurality of
physiological parameters and using the results to promote, demote,
or suppress alarm notification. The present specification provides
the benefits of producing more specific patient alarms and reducing
the occurrence of false alarms, thereby permitting the monitoring
personnel to perform more effectively.
[0026] In one embodiment, ECG parameters are considered with any
one, or a combination of, the following sensor measurements:
Invasive Blood Pressure (IBP); Non-Invasive Blood Pressure (NIBP);
and, Blood Oxygen Level (SpO.sub.2), such as via pulse oximetry.
For each parameter there is a corresponding waveform signal that is
created by measuring and sampling the signal off of a
transducer.
[0027] For ECG, a waveform is derived from an electrical signal
detected by cutaneously placed electrodes which respond to the
propagation of electrical signals in heart muscles. In one
embodiment, IBP uses an indwelling catheter with a transducer to
create a voltage proportional to the pressure which results from
the mechanical pumping action of the heart.
[0028] NIBP measurements are obtained via an external cuff coupled
with an electronic pressure transducer. The cuff is automatically
inflated and deflated at regular intervals to measure pressure
oscillations. While NIBP is used to measure blood pressure,
typically the pulse rate is also determined and reported as part of
that process. For example, a caregiver may establish or set up a
monitor to take an NIBP measurement every 15 minutes. This is
typical in an operating room (OR) or in the post-anesthesia care
unit (PACU) settings. Once every 15 minutes an NIBP measurement
might report a value such as "120/80 (92) HR 77" (i.e. systolic
pressure=120 mmHg, diastolic pressure=80 mmHg, mean arterial
pressure=92 mmHg, and pulse rate=77 bpm). In this scenario, the
NIBP parameter essentially provides an independent measure of pulse
rate but only does so every 15 minutes.
[0029] In another embodiment, for purposes of the present
specification, the cuff is inflated periodically, such as once
every few minutes to a pressure adequate to measure the pulse rate.
In one embodiment, the cuff is inflated to a diastolic pressure
equal to or slightly greater than the most recently measured
diastolic pressure. In another embodiment, the cuff is inflated to
a mean arterial pressure equal to or slightly greater than the most
recently measured mean arterial pressure. In another embodiment,
the cuff is inflated so that both the diastolic pressure and mean
arterial pressure are equal to or slightly greater than the most
recently measured corresponding pressure. Pulses detected while the
cuff is inflated are used as an alternate source of pulse
information in the same way as described for IBP and SpO.sub.2.
[0030] In yet another embodiment, NIBP is used to measure the
strength and regularity of the pulse signal in addition to the
pulse rate.
[0031] SpO.sub.2 waveforms are derived by measuring variations in
the amount of light detected by a photo-receptor after the light is
shined through a patient's skin. The anatomical site used must have
arterial blood flowing through it in sufficient quantity, such as,
a fingertip or ear.
[0032] In any case, for each parameter, a signal is created which
corresponds to either the electrical activity at the heart or the
pumping action of the heart and its subsequent propagation into the
periphery of the body. The individual parameters provide the
caregiver with independent means of verifying agreement between
results obtained via the electrical signal collected at the skin
(ECG) and the mechanical response measured as pulse signals via
invasive pressure lines (IBP), an external cuff (NIBP), or a pulse
oximeter (SpO.sub.2).
[0033] Further, when monitoring of the patient begins, each
waveform is processed independently to produce a record of where
each event (beat or pulse) occurs and to measure and record many
parameters of each event. For each ECG event (i.e. heartbeat) the
system measures and records the height and direction of the
waveform deflections in multiple leads and records if the
deflection pattern is typical and if it fell in the expected place
in the sequence based on the previous events. In addition, other
factors such as duration, rate of change, and locations of local
minima and maxima within each lead are recorded. Ultimately, all
recorded measurements are combined and compared to the previous
beats and a diagnosis as to whether the beat is representative of
"normal" or "abnormal" conduction is made.
[0034] For the purposes of the current specification, determining
whether an alarm should be issued is a function of the time of
occurrence of an ECG signal, (usually indexed off a prominent
feature of the ECG waveform), whether the ECG signal designation is
"normal" or "abnormal", and an estimate of the system's confidence
in the beat's diagnosis. If the beat was normal in all measured
parameters (closely matched preceding beats), occurred at the
expected time, and all other measures of signal consistency and
quality are high, the system will have high confidence that this
signal is reliable, e.g. a confidence in excess of a predetermined
threshold. All features measured by the ECG signal processing
algorithm are reported to the signal correlation software module
which then processes the data to generate the confidence level and
compare the confidence level to a threshold. Similarly, other
waveform parameters are recorded and reported (such as, but not
limited to IBP, NIBP, and SpO2), including measurements for time of
occurrence, amplitude, duration, peak change rates, and signal
quality to the signal correlation software module.
[0035] Measured feature data from each parameter is combined using
the signal correlation software module. In normal conditions, each
electrical pulse, as measured by ECG, produces a pulse response
which is also measured in the other parameters. Over time a
relationship between time of occurrence, signal amplitude, pulse
duration, noise level and confidence is created. When the signal
quality is good, and each ECG complex is capturing a good
mechanical response in the heart, and each of the other parameters
is generating a good pulse response, the agreement or correlation
between the each parameter is very high.
[0036] In one embodiment, when an abnormal beat (early or late,
atrial or ventricular ectopic) is detected via ECG, there is a
strong possibility of a reduced pulse response in one of the other
parameters. If this ectopic beat occurs with some frequency, then a
pattern is established between the ECG detecting "abnormal"
conduction and the reduced pulse response in the other parameters.
This pattern is recognized by the system as exhibiting a high
confidence for representing a real event, thereby triggering an
alarm.
[0037] In one embodiment, when the ECG signal is affected by noise
(usually a result of patient movement) and an "abnormal" conduction
is reported, the other parameters report normal pulse response. In
this embodiment, the conduction is actually "normal" but the ECG
signal is obscured by noise. The information from the other
parameters (good and consistent pulse signal at the expected time
with high confidence) is used to suppress any alarm or notification
about the abnormal beat. The ECG then uses the information gathered
from the other parameters to reconsider its diagnosis entirely.
Similarly, the feedback from the pulse sources can help demote or
suppress high and low pulse rate alarms and asystole alarms that
are due to signal quality issues at the ECG electrodes. This is a
result of having established a previous high correlation between
the ECG and pulse sources. When the data from the pulse sources is
of good quality and produces the expected results the system can
suppress or demote the alarm from the ECG source.
[0038] Conversely, when an actual event occurs, such as an
asystolic pause (the heart stops beating), the ECG will detect and
report no activity and the pulse sources will detect and report no
pulse responses. All these parameters together are producing
signals which are closely correlated and suggest the heart has
stopped. The system will then trigger an alarm with the highest
urgency.
[0039] The present invention is directed towards multiple
embodiments. The following disclosure is provided in order to
enable a person having ordinary skill in the art to practice the
invention. Language used in this specification should not be
interpreted as a general disavowal of any one specific embodiment
or used to limit the claims beyond the meaning of the terms used
therein. The general principles defined herein may be applied to
other embodiments and applications without departing from the
spirit and scope of the invention. Also, the terminology and
phraseology used is for the purpose of describing exemplary
embodiments and should not be considered limiting. Thus, the
present invention is to be accorded the widest scope encompassing
numerous alternatives, modifications and equivalents consistent
with the principles and features disclosed. For purpose of clarity,
details relating to technical material that is known in the
technical fields related to the invention have not been described
in detail so as not to unnecessarily obscure the present
invention.
[0040] FIG. 1 shows a flow diagram depicting a method of analyzing
a plurality of parameters to establish alarm hierarchy, in terms of
the alarm's significance, thereby determining if an alarm is to be
presented (via audio or visible signal) to a caregiver. In one
embodiment of the multi-parameter alarm hierarchy method of the
present invention, ECG parameters are considered in conjunction
with IBP (Invasive Blood Pressure), NIBP (Non-Invasive Blood
Pressure), and/or SpO.sub.2 (Blood oxygen level, such as via pulse
oximetry techniques) sensor measurements. To begin with, parameters
such as the time of occurrence, signal strength, amplitude and
regularity of every pulse signal, recorded by an IBP, NIBP, and/or
SpO.sub.2 sensor, are measured/recorded 105. Thereafter, at step
110 a one-to-one correlation is developed between each measured ECG
complex and the resultant pulse signal as measured on IBP, NIBP,
and/or SpO.sub.2.
[0041] In step 115, the correlation between the pulse sources (that
is, IBP, NIBP, and SpO.sub.2 sensors) and the ECG signal is
continuously monitored and analyzed. Heart rate alarm condition is
determined, in step 120, after giving due consideration to the
composite pulse rate readings from the IBP, NIBP, and/or SpO.sub.2
sensors and the ECG to improve the overall level of confidence for
an alarm situation. If the overall level of confidence is high,
such as when parameters from multiple sources are in tandem, in
step 125 an alarm is sounded or promoted. However, if the level of
confidence is low, such as when parameters from relevant multiple
sources are not in agreement with each other, then in step 130, the
alarm is suppressed or demoted.
[0042] In one embodiment, for example, false ECG arrhythmia alarms
are detected and suppressed, using the aforementioned method of the
present invention, by simultaneously observing pulse signals from
invasive pressure sensor, cuff pressure sensor, and/or the pulse
oximeter and when adequate confidence in the pulse signal(s) allows
the suppression of the ECG based alarm. Thus, if a sufficiently
strong rhythmic pulse signal as measured on IBP, NIBP, and
SpO.sub.2 sensors is present, then there exists a reasonable
certainty that the patient is not experiencing arrhythmia. In such
example, an ECG alarm will be demoted or suppressed in the
hierarchy of alarms to be sounded to a caregiver, in accordance
with the method of the present invention, thereby avoiding false
alarms related to arrhythmia conditions such as asystole,
ventricular tachycardia, ventricular couplets and ventricular runs.
Similarly, an ECG arrhythmia alarm is promoted if the condition is
confirmed or corroborated by information form the pulse signal
sources of IBP, NIBP, and/or SpO.sub.2. For example, an ectopic
beat will often create less pulse pressure and blood flow. This
decreased peripheral pressure or flow can be detected on the
SpO.sub.2 signal, external cuff, and/or an arterial pressure line.
The presence of the reduced signal in the Spo.sub.2, cuff, and/or
pressure lines confirms or increases the confidence to label those
beats as ectopic beats.
[0043] FIG. 2a is a graphical representation of an ECG (III) signal
200 with waveform noise 205 and a corresponding IBP (ART) signal
201 showing normal cardiac activity 210 for the same interval. This
figure shows an ECG waveform 200 with noise 205 closely resembling
ventricular tachycardia, which would normally generate a high
priority alarm. However, because the simultaneous IBP waveform 201
clearly shows continuing pulse with very regular rhythm and
amplitude 210, this high priority alarm is demoted to a low
priority alarm indicating "Noisy ECG". FIG. 2b is a graphical
representation of an ECG (III) signal 202 with waveform noise 220
and a corresponding IBP (ART) signal 203 showing lack of cardiac
activity 225 for the same interval. This figure shows an episode of
ventricular tachycardia 220 which is confirmed by the cessation of
pulsatile activity 225 in the invasive pressure waveform. Due to
the great degree of correlation between the signals obtained from
the two independent measurements, a high priority alarm is
promoted.
[0044] FIG. 3a is a graphical representation showing
plethysmograph-assisted analysis for atrial ectopic beats. As
observable in the waveform of FIG. 3a, a weak SpO.sub.2
plethysmograph signal 305 confirms ectopic beats 310 in the ECG
waveform.
[0045] FIG. 3b is a graphical representation of ECG (V1) 311, ECG2
(II) 312 and SpO.sub.2 313 signals at time T.sub.0 for
plethysmograph-assisted ventricular beat analysis and FIG. 3c is a
graphical representation of ECG (V1) 321, ECG2 (II) 322 and
SpO.sub.2 323 signals at time T.sub.1 for plethysmograph-assisted
ECG signal noise analysis. Now referring to FIG. 3b, the
ventricular beat, V, is corroborated or confirmed in the SpO.sub.2
graph 313 that correspondingly shows little or no signal response
315. This corroboration improves the overall confidence thereby
promoting a heart rate alarm condition. However, as the ECG data
gets noisy at the end of the strip 320, shown in FIG. 3b, and the
beginning of the strip 325, shown in FIG. 3c, the correlated
SpO.sub.2 waveforms provide confirmation that none of the noise is
likely a real beat. This allows for demotion or suppression of a
heart rate alarm that would otherwise have been sounded if
SpO.sub.2 waveform was not considered and the ECG heart rate
parameter were relied upon in isolation.
[0046] In another embodiment, a NIBP (Non-Invasive Blood Pressure)
cuff is used as an alternative signal source in the same way as IBP
and/or SpO.sub.2, when necessary. The system will inflate the cuff
periodically and also when the primary heart rate sources (ECG,
IBP, SpO.sub.2) are unavailable, in disagreement, or indicate a
serious condition that needs to be verified. The system will
perform periodic inflations and also on-demand inflation as
described below.
[0047] For example, in one embodiment, a patient is monitored on
NIBP and ECG only. The patient inadvertently removes some or all of
their ECG electrodes such that the ECG parameter is effectively
disabled. At this point the cuff inflates and begins "backup"
monitoring of the pulse with NIBP. If the NIBP is producing a
reasonable "in-bounds" pulse signal the system propagates a
low-priority alarm to the caregiver ("Check ECG leads" or "Signal
unavailable").
[0048] However, if the pulse rate is indicating an alarm condition
(such as no pulse, high rate, low rate, or very different pulse
strength or regularity than previously measured), the alarm message
is elevated to a clinical alarm such as "ECG unavailable NIBP
indicating pulse rate>120 bpm-Check Patient".
[0049] In another example, if an ECG analysis suggests a rhythm
change to atrial fibrillation, the
[0050] NIBP cuff on the patient is inflated in order to monitor the
strength and regularity of the pulse measured in the NIBP cuff.
This additional NIBP data is then used to confirm or suppress the
atrial fibrillation diagnosis. Similarly, out of bounds heart rate
alarms are checked via the NIBP cuff to confirm or deny rate
violations before the alarm is sounded.
[0051] Persons of ordinary skill in the art should note that a
plurality of other combinations of parameters can be utilized in
accordance with the alarm hierarchy determination method of the
present invention and that the use of parameters such as ECG, IBP,
NIBP, and/or SpO.sub.2 is only by way of a non-limiting example.
However, it should be noted that the accurate suppression or
promotion of an alarm requires the careful correlation of different
physiological parameters to ensure that real events are being
tracked and reported. It should also be noted herein that the
occurrence of the ECG derived event is still reported as a
notification or display to a patient monitor, but not as a clinical
alarm, which is any visual or auditory signal designed to attract
human attention and is indicative of an abnormal physiological
state requiring immediate medical attention. This enables the
caregiver to review excluded events from the multi-parameter
analysis of the present invention.
[0052] According to another aspect of the present invention a
plurality of physiological cross-parameters are also analyzed to
determine alarm hierarchy. Persons of ordinary skill in the art
would appreciate that a respiration signal can be derived from
invasive blood pressure lines, depending on placement of a
catheter, the hemodynamic condition of the patient, and the
characteristics of respiration. In one embodiment, the invasive
pressure line signal, observable as a pulse pressure variation
which is driven by respiration, is used as a secondary respiration
signal. Thus, the invasive pressure line signal is used in
conjunction with a primary respiration signal source to confirm
respiration rate changes or to identify apnea events.
[0053] FIG. 4 is a graphical representation of invasive pressure
systolic peak modulation with respiration signals. Thus, FIG. 4
shows signal plots of how invasive pressure systolic peaks 405
modulate with respiration signals 410 in accordance with an
embodiment of the present invention. This modulation is measured
and used as a secondary source of respiration rate measurement. As
observable in FIG. 4, the relationship between the bio-impedance
respiration signal 410 and the invasive pressure signal 405 is
established in the first six seconds. As the bio-impedance signal
410 degrades, at 415, the pressure signal 405 is used to establish
the respiration rate even though the bio-impedance signal 410 is
temporarily unavailable, thereby suppressing a false respiration
rate related alarm. However, the fact that bio-impedance is
unavailable is still reported as an event and not as a clinical
alarm.
[0054] In one embodiment, a secondary respiration signal is derived
by monitoring changes in the amplitudes of ECG signal, in multiple
leads, during respiration cycle. These amplitude changes are a
result of the heart moving in the chest relative to the measuring
electrodes owing to movement of the chest and lungs during
respiration. This, in turn, creates another pseudo-respiration
signal that is used to confirm respiration changes when
studied/analyzed in conjunction with a primary source of
respiration signal, such as capnography, PRT (Pneumatic Respiration
Transducer), a strain or a stretch gauge or any bio-impedance
signal source known to persons of ordinary skill in the art. Since
the pseudo-signal is not expected to be present and therefore
reliable all the time (since in this embodiment the pseudo-signal
depends on chest/lung movement), the pseudo-signal is used only
when a high correlation is observed between the pseudo-signal and a
primary respiration signal.
[0055] In another embodiment, a secondary respiration signal is
derived by monitoring changes in the amplitudes of the SpO.sub.2
plethysmograph or small changes in the oxygen saturation signal
during the respiration cycle. These amplitude changes are a result
of the heart moving in the chest owing to movement of the chest and
lungs during respiration, thus creating another pseudo-respiration
signal that is used to confirm respiration changes when
studied/analyzed in conjunction with a primary source of
respiration signal.
[0056] In one embodiment, motion signals from a motion detecting
accelerometer are used as pseudo or secondary respiration signals
in conjunction with a primary source of respiration signals. In one
embodiment of the present invention, an accelerometer is integrated
into an electrode wire snap thereby rendering the accelerometer
virtually reusable with very low disposable cost.
[0057] FIG. 5a is an illustration of one embodiment of a disposable
ECG electrode while FIG. 5b is an illustration of the disposable
ECG electrode shown in FIG. 5a further showing a reusable snap
electrode wire.
[0058] In one embodiment of the present invention, an accelerometer
(not shown) is integrated into the electrode wire snap 505. In one
embodiment, as shown in FIG. 5c, the electrode wire is attached to
the ECG electrode 500. In one embodiment, a tri-axial accelerometer
is used, such as, but not limited to, the ADXL330 3-axis iMEMS.RTM.
accelerometer from Analog Devices. Persons of ordinary skill in the
art should appreciate that the accelerometer can be integrated into
other devices, apart from ECG electrodes, such as a cell-phone or
other devices like the iPod.TM. from Apple.TM..
[0059] In one embodiment the spatial orientation of the
accelerometer is maintained such that it is consistently applied in
the same orientation relative to a patient. To enable this,
mechanical fixtures such as locking snaps, tabs or adhesives are
used to position, align and lock the accelerometer snap
consistently into a position. In one embodiment, markings, such as
a note saying "this end up", are placed on the
electrode/accelerometer along with a locking tab or any other
mechanical fixture to ensure that the accelerometer is always
oriented the same way relative to the body and stays in this
position. The accelerometer integrated ECG electrode is
appropriately placed on a patient such that the position allows for
maximized chest wall motion. Persons of ordinary skill in the art
should appreciate that the accelerometer can be used as integrated
with an ECG electrode and/or on a standalone basis. In one
embodiment, two or more different 3-axis accelerometers are used
and positioned in multiple locations on the patient's torso in
order to maximize detection of measured quantities.
[0060] In situations where only the accelerometer signals are
available while other primary respiration signals are unusable or
unavailable--the accelerometer data is used as a proxy
"dead-in-bed" detector which sounds an alarm when no movement or
respiration signal is present. However, in situations where another
source of primary respiration signal (such as bio impedance, stress
or strain gauge, capnography) is available, the accelerometer
signal is used to validate the primary respiration signal. Thus,
when the accelerometer measurements are in agreement with other
primary source(s) of measurement, there is increased confidence
that the measured signal is correct and an alarm is sounded to the
caregiver. However, data from the proxy accelerometer signal is
used to suppress false alarms (for conditions such as low or high
breath rate, apnea) from other respiration signal sources when the
signal from the accelerometer indicates a different respiration
signal with sufficiently high confidence. Thus, data from a
plurality of sources is co-analyzed to produce a more robust
measurement of respiration. This increases the quality of the
respiration signal analysis and reduces unnecessary alarms for the
caregiver.
[0061] According to one aspect of the present invention, motion
signals from an accelerometer are used to determine and monitor
patient posture. For example, the amount of time a patient spends
in standing, sitting, active and/or supine positions is calculated
and reported.
[0062] FIG. 6 is a graphical representation of chest wall movement
in a patient wearing an accelerometer while supine. A 3-axis
accelerometer measures applied force in each of 3 different
orthogonal directions. FIG. 6 depicts a graphical representation of
the signal created by a chest worn accelerometer for a patient
while lying down. The data represents 1 minute in time and shows
the signal from each axis of the accelerometer. The effects of
respiration can be seen in FIG. 6, particularly in waveform G 605
and waveform Y 610 and, to a lesser extent, in waveform B 615.
Waveform G's 605 mean signal is about 300 counts, waveform Y's 610
is about -150 counts, and waveform B's 615 is -350 counts.
[0063] FIG. 7 is a graphical representation of chest wall movement
in the same patient wearing an accelerometer after standing up. The
positional change of the patient thus results in dramatic changes
in the mean levels of each signal. In comparison with a supine
patient, waveform G's 705 mean level is now -130 counts, waveform
Y's 710 is -650 counts, and waveform B's 715 is 150 counts. This
effect is a result of the change in spatial orientation of the
3-axis accelerometer relative to the gravitational field of the
earth. Provided that the accelerometer is attached to the patient
in the same orientation each time, then the relative mean values of
the signal off each axis will tell the clinician if the patient is
"upright" (could be standing or sitting), supine, or perhaps
partially propped up with pillows if between an upright and supine
position.
[0064] This information is useful in assessing discharge decisions
from a monitoring perspective. Similarly, sleep positions, such as
on back, left side, right side, stomach, are monitored. In one
embodiment, the number of position changes per hour is measured and
quantified and used in conjunction with motion measurements from
accelerometer to determine if a patients overall activity is what
would be expected for a patient in a given state. For example,
detection of lack of motion or posture change is notified to a
caregiver as a need for the patient to be turned in bed to prevent
bed sores.
[0065] In another embodiment, data collected by the accelerometer
signifying position changes is used to detect falls and trigger
alarm notification. For example, waveform signatures denoting a
sudden change from a standing position to a supine position
preceded by an impact would alert the system of a possible patient
fall. The system would then promote or trigger an alarm
notification.
[0066] According to another aspect of the present invention, apart
from monitoring patient posture, accelerometer signals are also
used to measure patient activity. In one embodiment, accelerometer
signals are used to both count and record patient steps and patient
step rates.
[0067] FIG. 8 is a graphical representation of chest wall movement
in the same patient wearing an accelerometer while walking. The
time axis represents 10 seconds of data collected while the patient
was walking. The walking signature is quite different from the
supine and standing signatures depicted in FIG. 6 and FIG. 7,
respectively. The user can easily pick out each footfall (in
waveform Y 810 and waveform G 805 in particular) and to see that in
10 seconds approximately 19 steps were taken. The actual steps
could be measured by looking across all 3 bands for the
characteristic rapid changes in each axis signal. These events can
be counted (pedometer type function) and reported as a count or as
a rate; for example, in this ten second time period, the event can
be represented as 19 total steps or 114 steps per minute.
[0068] This information is used to calculate statistics such as the
percentage of time the patient spends walking and at what step
rates. Such statistics when analyzed in the long term over hours
and days, in one embodiment, help in assessing ambulatory patients
for parameters such as how much they are moving, how does their
activity level compare to similar patients, whether or not they are
candidates for discharge, and/or any other parameters as would be
advantageously evident to persons of ordinary skill in the art.
[0069] According to another aspect of the present invention, the
accelerometer signals are used to detect motion/activity artifacts
induced signal changes in other physiological parameters being
monitored for the patient. In one embodiment this is useful in
suppressing or demoting an alarm situation during heightened
patient activity. For example, respiration measurements by methods
such as bio-impedance and pulse oximetry can be seriously
compromised by patient gross motion. Persons of ordinary skill in
the art would appreciate that ECG signal can be compromised by
motion. To assess motion induced artifacts, an analysis of motion
signal from the accelerometer is used to correlate specific noise
in the ECG signal with specific patient motion activity, including
walking. Such sufficiently positive correlation enables false ECG
alarms to be suppressed. In another embodiment use of accelerometer
signals in conjunction with other physiological parameters enables
improvement in the level of confidence for an alarm situation. For
example, a possible marginal arrhythmia detected on the ECG which
accompanied by a motion signal consistent with fainting is promoted
to a higher alarm priority.
[0070] In another embodiment, changes in patient posture detected
using the accelerometer is used to analyze and interpret measured
changes in ECG ST Segment. It is well-known to those of ordinary
skill in the art that the ST Segment is a portion of the ECG
waveform which is monitored to identify ongoing myocardial
infarction. Sometimes the ST Segment levels change with patient
position as a result of the movement of the heart inside the chest
relative to the ECG electrodes. ST segment changes due to position
change are, however, not significant. Accelerometer signals provide
necessary information conveying that positional changes preceded ST
segment changes thereby enabling demotion of the alarm significance
of an ST segment change.
[0071] According to one aspect of the present invention, motion
signals from the accelerometer are used to modify overall
sensitivity of the patient alarm system. In one embodiment, if the
accelerometer signal analysis strongly suggests that the patient is
walking or is very active the sensitivity of alarm system in the
monitor is appropriately reduced. The objective here is to reduce
false alarms that are induced by patient activity. According to
another aspect of the present invention, patient activity level,
monitored with accelerometer signals, is used to vary the need and
kind of analysis that is performed on other physiological
parameters. For example if the patient activity level is high due
to activities such as walking or using a treadmill, then an ECG
analysis for the patient is suspended during the period of the
activity as ECG analysis requires high signal quality. Instead, in
one embodiment, the overall sensitivity levels of the alarm system
is pared down so that motion induced noise signals do not trigger
false alarms while the some basic parameter analysis is
continued.
[0072] According to a yet another aspect of the present invention,
heart valve sounds are measured (such as by placing a microphone on
the chest) to monitor mechanical activity of the heart to improve
overall patient monitoring and also to reduce false alarms.
[0073] In one embodiment, heart valve sounds are used as a measure
of patient pulse activity. The valve sounds from the heart form an
independent pulse signal which is used to differentiate noise from
signal at the ECG electrodes. As a first step, valve sound
signature which matches each QRS location detected on an ECG is
identified and recorded. In the next step, the quality of the
recorded valve sound signals is determined based on parameters such
as the strength, consistency, quality and regularity of the sound
signal on a beat to beat basis. The determined sound quality
measurement or signal to noise ratio is estimated on a continuous
basis. The resultant valve sound quality is thereafter used to
weigh how strongly the data from the sound channel (such as a
microphone placed on the patient's chest) is used to promote or
suppress alarm data from other physiological parameter measuring
channels/sources such as ECG electrodes.
[0074] In another embodiment valve sounds from the heart form an
independent pulse signal which are used to identify non-perfusing
beats and pulseless electrical activity. It should be understood by
persons of ordinary skill in the art that pulseless electrical
activity is a general case of electromechanical disassociation in
the heart. In some arrhythmia cases it is advantageous to identify
beats for which there is no mechanical response. In other words,
these beats are non-perfusing in that they have an electrical
signal (probably abnormal) but do not cause the heart to pump. For
example, there are cases in which pacemakers induce electrical
signals in the heart which are detected by the ECG parameter, but
which do not produce effective mechanical pumping. In this case,
mechanical response, by way of valve sound signals measured on a
beat by beat basis, in conjunction with ECG signals, enable
identification of such events and alarm appropriately. For example,
if an arrhythmia event detected at the ECG is verified by the valve
sound signal there is an increased probability that this is a real
event and would enable promoting this alarm due to the increased
confidence in the correctness of the alarm. Such a scenario exists,
for example, if the ECG analysis suggests a pause or asystole (no
beats detected) and the heart valve sound signal also suggests no
mechanical motion. This is a case of confirmed pause or asystole
diagnosis and this alarm is promoted with confidence. Similarly, if
an event is detected by the ECG but is not indicated by the heart
valve sound signal, then the event alarm is suppressed or demoted.
For example, the ECG signal may indicate a run of irregular beats
that suggests a ventricular tachycardia. However, a high quality
heart valve sound signal suggests that the pulse rate does not
match the irregular beats that the ECG analysis is detecting.
Therefore, in this case the alarm for the irregular beats is
suppressed or demoted.
* * * * *