U.S. patent application number 17/142496 was filed with the patent office on 2021-08-19 for method for determining vascular access risk in a hemodialysis patient population.
The applicant listed for this patent is Henry Ford Health System. Invention is credited to Brad ASTOR, Anatole BESARAB, Douglas CURRY, Stanley FRINAK, Helen Kimball HIRSCHMAN, John KENNEDY, Lalathaksha KUMBAR, Jeffrey J. SANDS, Jerry YEE, Gerard ZASUWA.
Application Number | 20210257102 17/142496 |
Document ID | / |
Family ID | 1000005557076 |
Filed Date | 2021-08-19 |
United States Patent
Application |
20210257102 |
Kind Code |
A1 |
KENNEDY; John ; et
al. |
August 19, 2021 |
METHOD FOR DETERMINING VASCULAR ACCESS RISK IN A HEMODIALYSIS
PATIENT POPULATION
Abstract
A method for determining risk of an adverse event, such as
thrombosis or a required intervention, associated with a vascular
access includes receiving hemodialysis treatment data associated
with the vascular access, deriving a plurality of selected risk
factors from the hemodialysis treatment data, evaluating the
plurality of selected risk factors over a time period, assigning
raw scores to each selected risk factor based on its values over
the time period, summing the raw scores for the plurality of
selected risk factors to determine a cumulative raw score, and
correlating the cumulative raw score with a level of risk of an
adverse event associated with the vascular access.
Inventors: |
KENNEDY; John; (Evanston,
IL) ; ASTOR; Brad; (Madison, WI) ; SANDS;
Jeffrey J.; (Orlando, FL) ; HIRSCHMAN; Helen
Kimball; (Evanston, IL) ; CURRY; Douglas;
(West Lafayette, IN) ; FRINAK; Stanley;
(Farmington Hills, MI) ; ZASUWA; Gerard; (West
Bloomfield, MI) ; YEE; Jerry; (Beverly Hills, MI)
; BESARAB; Anatole; (Bloomfield Hills, MI) ;
KUMBAR; Lalathaksha; (Troy, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Henry Ford Health System |
Detroit |
MI |
US |
|
|
Family ID: |
1000005557076 |
Appl. No.: |
17/142496 |
Filed: |
January 6, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16577574 |
Sep 20, 2019 |
10916349 |
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17142496 |
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62734556 |
Sep 21, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G16H 10/60 20180101;
G16H 50/70 20180101; G16H 50/30 20180101 |
International
Class: |
G16H 50/30 20060101
G16H050/30; G16H 50/70 20060101 G16H050/70; G16H 10/60 20060101
G16H010/60 |
Claims
1. A method for determining risk of an adverse event associated
with a vascular access, the method comprising: receiving
hemodialysis treatment data associated with the vascular access;
deriving a plurality of selected risk factors from the hemodialysis
treatment data; evaluating the plurality of selected risk factors
over a time period; assigning raw scores to each selected risk
factor based on its values over the time period; summing the raw
scores for the plurality of selected risk factors to determine a
cumulative raw score; and correlating the cumulative raw score with
a level of risk of an adverse event associated with the vascular
access.
2. The method of claim 1, wherein correlating the cumulative raw
score with a level of risk includes correlating the cumulative raw
score with a final risk score, wherein a higher final risk score is
associated with a higher probability of an adverse event for the
vascular access.
3. The method of claim 1, further comprising prioritizing the
vascular access for risk of an adverse event among a hemodialysis
patient population.
4. The method of claim 1, wherein the adverse event includes at
least one of thrombosis or intervention required for the vascular
access.
5. The method of claim 1, wherein the hemodialysis treatment data
includes venous access pressure (VAP), arterial access pressure
(AAP), and mean arterial pressure (MAP), and the method further
includes calculating a venous access pressure ratio (VAPR) by
normalizing VAP with respect MAP and calculating an arterial access
pressure ratio (AAPR) by normalizing AAP with respect to MAP.
6. The method of claim 1, wherein the plurality of selected risk
factors includes the number of VAPR and AAPR alerts for exceeding a
threshold pressure level over the time period.
7. The method of claim 1, wherein the plurality of selected risk
factors includes the average VAPR over the time period.
8. The method of claim 1, wherein the plurality of selected risk
factors includes the average AAPR over the time period.
9. The method of claim 1, wherein the plurality of selected risk
factors includes the slope of VAPR over the time period.
10. The method of claim 1, wherein the plurality of selected risk
factors includes a number of hemodialysis treatments that do not
achieve at least 90% of a prescribed blood flow rate.
11. The method of claim 1, wherein the cumulative raw score is
categorized based on a type and location of the vascular
access.
12. A method for determining risk of an adverse event associated
with a vascular access, the method comprising: evaluating
hemodialysis treatment data associated with the vascular access to
derive a plurality of selected risk factors relating to VAPR, AAPR
and blood flow rate; evaluating the plurality of selected risk
factors over a time period; assigning raw scores to each selected
risk factor based on its values over the time period; summing the
raw scores for the plurality of selected risk factors to determine
a cumulative raw score; and correlating the cumulative raw score
with a final risk score indicative of a probability of an adverse
event associated with the vascular access.
13. The method of claim 12, further comprising prioritizing the
vascular access for risk of an adverse event among a hemodialysis
patient population.
14. The method of claim 12, wherein the adverse event includes at
least one of thrombosis or intervention required for the vascular
access.
15. The method of claim 12, wherein the plurality of selected risk
factors includes the number of VAPR and AAPR alerts for exceeding a
threshold pressure level over the time period.
16. The method of claim 12, wherein the plurality of selected risk
factors includes the average VAPR and average AAPR over the time
period.
17. The method of claim 12, wherein the plurality of selected risk
factors includes the slope of VAPR over the time period.
18. The method of claim 12, wherein the plurality of selected risk
factors includes a number of hemodialysis treatments that do not
achieve at least 90% of a prescribed blood flow rate.
19. The method of claim 12, wherein the cumulative raw score is
categorized based on a type and location of the vascular
access.
20. A method for determining risk of thrombosis or a required
intervention associated with a vascular access, the method
comprising: receiving hemodialysis treatment data associated with
the vascular access; deriving a plurality of selected risk factors
from the hemodialysis treatment data, the plurality of selected
risk factors relating to VAPR, AAPR and blood flow rate; evaluating
the plurality of selected risk factors over a time period to
determine risk factor values including averages, slopes, and number
of alerts; assigning raw scores to each selected risk factor based
on its values over the time period; summing the raw scores for the
plurality of selected risk factors to determine a cumulative raw
score; correlating the cumulative raw score with a final risk score
indicative of a probability of thrombosis or a required
intervention associated with the vascular access; and prioritizing
the vascular access for risk of thrombosis or a required
intervention among a hemodialysis patient population.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/577,574 filed Sep. 20, 2019, which, in turn, claims the
benefit of U.S. provisional application Ser. No. 62/734,556 filed
Sep. 21, 2018, the disclosures of which are hereby incorporated in
their entirety by reference herein.
TECHNICAL FIELD
[0002] Embodiments relate to a method for determining risk of an
adverse event associated with a vascular access, such as thrombosis
or a required intervention.
BACKGROUND
[0003] Patients who lose the use of their kidneys must undergo
hemodialysis to remove fluids and toxins from the body. This
requires the existence of a vascular access in order to remove the
blood for treatment and then return it to the body. The preferred
vascular access is an arteriovenous (AV) access (either an AV
fistula--AVF or AV graft--AVG) created by joining an artery to a
vein directly (AVF) or by interposing an artificial vessel to
connect the artery to the vein (AVG). There are only a limited
number of sites on the body where an AV access can be placed, so
preserving these sites is critical. Unfortunately, stenosis (growth
of a lesion inside the vessel wall) may develop over time and can
lead to a thrombosis. The procedures used to reopen a thrombosed
access are invasive, and even if successful this procedure can
cause damage to the access which may shorten its life. There are
elective interventional procedures that can mitigate the onset of
stenosis, but knowing when to refer a patient for these preventive
procedures has been a challenge.
SUMMARY
[0004] In one or more embodiments, a method for determining risk of
an adverse event associated with a vascular access includes
receiving hemodialysis treatment data associated with the vascular
access, deriving a plurality of selected risk factors from the
hemodialysis treatment data, evaluating the plurality of selected
risk factors over a time period, assigning raw scores to each
selected risk factor based on its values over the time period,
summing the raw scores for the plurality of selected risk factors
to determine a cumulative raw score, and correlating the cumulative
raw score with a level of risk of an adverse event associated with
the vascular access.
[0005] In one or more embodiments, a method for determining risk of
an adverse event associated with a vascular access includes
evaluating hemodialysis treatment data associated with the vascular
access to derive a plurality of selected risk factors relating to
venous access pressure ration (VAPR), arterial access pressure
ratio (AAPR) and blood flow rate, evaluating the plurality of
selected risk factors over a time period, assigning raw scores to
each selected risk factor based on its values over the time period,
summing the raw scores for the plurality of selected risk factors
to determine a cumulative raw score, and correlating the cumulative
raw score with a final risk score indicative of a probability of an
adverse event associated with the vascular access.
[0006] In one or more embodiments, a method for determining risk of
thrombosis or a required intervention associated with a vascular
access includes receiving hemodialysis treatment data associated
with the vascular access, deriving a plurality of selected risk
factors from the hemodialysis treatment data, the plurality of
selected risk factors relating to VAPR, AAPR and blood flow rate,
evaluating the plurality of selected risk factors over a time
period to determine risk factor values including averages, slopes,
and number of alerts, assigning raw scores to each selected risk
factor based on its values over the time period, summing the raw
scores for the plurality of selected risk factors to determine a
cumulative raw score, correlating the cumulative raw score with a
final risk score indicative of a probability of thrombosis or a
required intervention associated with the vascular access, and
prioritizing the vascular access for risk of thrombosis or a
required intervention among a hemodialysis patient population.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a graph of venous access pressure ratio (VAPR) in
an AVG over time illustrating the factors of density (number of
alerts), severity (how high is the pressure), and slope which
together relate to the risk of access complications;
[0008] FIG. 2 is a schematic illustration of data obtained during a
hemodialysis treatment session for a patient, wherein data for a
plurality of treatment sessions may be stored in a database;
[0009] FIG. 3 is a schematic illustration of calculating risk
factors such as VAPR, arterial access pressure ratio (AAPR), and
blood flow from the hemodialysis treatment data, and then
evaluating these risk factors over time to determine, for example,
average VAPR, VAPR slope, number of VAPR alerts, average AAPR, and
blood flow <90% prescribed;
[0010] FIG. 4 is a chart illustrating the influence of vascular
access location on the final risk score;
[0011] FIG. 5 is a chart depicting the probability of any
intervention and the proportion of the study patient population by
final risk score for AVF;
[0012] FIG. 6 is a chart depicting the probability of any
intervention and the proportion of the study patient population by
final risk score for AVG;
[0013] FIG. 7 is a graph showing the relative risk of complication
as a function of VAPR slope for an AVF, where the greater the slope
upward (right of center) or downward (left of center) indicates
increasing risk;
[0014] FIG. 8 shows data that can obtained during a patient's
hemodialysis treatment and parameters can be continuously
calculated during the hemodialysis treatment that can be included
in the scoring to determine the risk of a hypotensive event during
hemodialysis; and
[0015] FIG. 9 depicts an example of an actual patient's AAPR, VAPR,
and blood flow results showing the score each month over ten
months.
DETAILED DESCRIPTION
[0016] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale; some features may be exaggerated or
minimized to show details of particular components. Therefore,
specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a representative basis
for teaching one skilled in the art to variously employ the present
invention.
[0017] As a matter of background, hemodialysis machines utilize two
needles, one to remove blood from the patient (arterial) and one to
put the dialyzed blood back into the patient (venous needle).
During hemodialysis, blood is drawn from the vascular access
through the arterial needle by the hemodialysis machine blood pump.
After passage through the dialyzer, the blood traverses the venous
drip chamber and returns to the access through the venous needle.
The pressure required to infuse blood back into the access through
the venous tubing and access needle and to overcome the pressure
within the access is recorded as the venous drip chamber pressure
(VDP). One component of VDP is the access pressure at the venous
needle site (venous access pressure (VAP)). Another component of
VDP is the combined pressure required to overcome the resistance to
flow through the tubing distal to the drip chamber (low) and
through the venous return needle (high). VDP is also a function of
needle size, tubing length and blood viscosity, represented by
hematocrit. If the venous pressure within an access at the needle
site is 0 mmHg, VDP can be defined as VDP.sub.0, i.e., the venous
drip chamber pressure when the access pressure is zero.
Consequently, VDP.sub.0 can be calculated for a given hemodialysis
machine, tubing set, and needle size when the blood flow rate and
hematocrit are measured. Once VDP.sub.0 is determined, VAP can be
calculated from the measured VDP: VAP=VDP-VDP.sub.0. To normalize
variations in VAP attributed to changes in mean arterial pressure
(MAP), the venous access pressure ratio (VAPR) is calculated:
VAPR=VAP/MAP. An arterial access pressure ratio (AAPR) can be
calculated in a corresponding manner.
[0018] There are many factors that should be considered by
nephrologists and dialysis staff before they can decide whether to
refer a patient for vascular access imaging and intervention. For
example, these factors may include whether the blood flow delivered
to the hemodialysis machine is steady and achieving the prescribed
goals, whether the hemodialysis treatments are achieving adequate
clearances for removing fluids and toxins, how many alerts (such as
AAPR and/or VAPR, and delivered blood flow) have occurred in the
last 30 to 60 days, how high both the arterial and venous
intra-access pressures are, the rate of change in the pressures
from treatment to treatment, the type of access (AVF or AVG), and
the past history of the access, to name a few.
[0019] The process of considering all of these factors when
evaluating a patient's risk of access complications takes time and
expertise. As a result, incorrect or non-optimal treatment
decisions may be made due to the time and focus required to compile
and digest all of the factors for consideration. While vascular
access surveillance can identify patients with AVF or AVG at high
risk of having stenosis which may lead to access thrombosis,
determining which patients' stenosis will cause thrombosis and the
lead time to these adverse events remains less clear. This type of
risk assessment is necessary to allow timely interventions for the
patients in need, and to avoid unnecessary procedures for other
patients.
[0020] U.S. Pat. No. 7,597,666 directed to a method of vascular
access surveillance is incorporated by reference herein in its
entirety. Hemodialysis treatment data is used to calculate
intra-access venous (VAPR) and arterial (AAPR) pressure ratios for
each treatment to identify whether a patient's vascular access is a
high risk for thrombosis and needing further evaluation and/or
elective intervention. In one embodiment, alerts may be generated
when the VAPR >0.55 or the AAPR >0.65 for AVF or AAPR
>0.60 for arteriovenous graft AVG on three consecutive
treatments. However, VAPR and AAPR are only two of the many factors
that can indicate risk of thrombosis or access complications.
[0021] While this method of vascular access surveillance provides a
reliable signal ("alert") that a patient has an increased risk for
vascular access complications, there is currently no mechanism to
prioritize one patient on an alert list over another. This task has
been left to nephrologists and facility staff to review, triage,
and individually assess the severity of the risk to determine which
patients should be referred and when this referral should take
place. However, in many busy facilities this individualized
approach has become impractical either due to lack of staff time or
lack of expertise.
[0022] The solution lies in creating a score that can prioritize
patients for risk. Accordingly, the system and method disclosed
herein include a multifactorial scoring algorithm to estimate the
risk of a patient developing vascular access thrombosis or
undergoing an intervention, such as over a time period (e.g.,
within the subsequent 60 days). The method disclosed herein
utilizes a selected subset of the risk factors that could be used
for triaging patients at high risk for an adverse vascular access
event. These risk factors may include a) the number of VAPR and
AAPR alerts, b) the average normalized VAPR, c) the average
normalized AAPR, d) the slope of the average normalized venous
pressure (VAPR) over time, e) the number of hemodialysis treatments
that do not achieve at least 90% of the prescribed blood flow, and
f) the location of the access. Other known risk factors for access
dysfunction can also be included, such as the slopes of the
averaged normalized arterial pressure (AAPR) over time, and the
past history of interventions performed on a specific access.
[0023] By combining the results of these risk factors into a
numeric `score`, problems with the vascular access may be better
anticipated in advance based on these individualized
patient-related factors. By providing an early indication of
increased risk for an adverse event, sufficient lead time may be
provided to allow time to schedule the patient for a proactive
intervention. By combining these risk factors and their relative
weighting (raw scores) for access complications into a simple
score, clinical staff is provided with a way to optimize the
prioritization process of selecting patients in need of having
their vascular access examined for possible intervention.
[0024] There are several quantifiable factors that relate to the
risk of access complications, and FIG. 1 illustrates three of these
risk factors. Density is the number of VAPR or AAPR alerts
(pressure threshold exceeded) in a given time period, where more
alerts indicate a higher risk. In the scoring method disclosed
herein, different time periods may be given different weights, such
that more recent results may carry more weight than prior results.
Severity is the relative pressure (AAPR, VAPR) in the access during
a given time period, where generally the higher the average
pressure, the higher the risk. Similarly, an increasing or
declining VAPR and/or AAPR may also indicate progressive stenosis
with declining access blood flow. Slope is the increasing (or
decreasing) pressure over time and may indicate how fast an
occlusion is growing, where the faster the growth, the higher the
risk. For example, slope may be calculated from the difference
between the average VAPR of the most recent time period compared
with a prior time period, or it may be derived by performing a
regression over a given time period. In the disclosed scoring
method, a steep slope may be weighted greater than a gradual
climb.
[0025] Additional known risk factors may also be included in the
scoring algorithm. For example, hemodialysis machine blood flow can
be evaluated to determine if the prescribed blood flow rate been
achieved in recent treatments. The more treatments not achieving
adequate and/or prescribed blood flow rate, the higher the risk.
The percentage of the prescribed blood flow actually being achieved
can be assessed, such as, but not limited to, the number of
treatments in a prior period where the average blood flow in a
treatment session was less than, for example, 90% of the prescribed
blood flow. This factor may be weighted greater for those patients
who have missed the prescribed blood flow by a higher
percentage.
[0026] There are many risk factors that could be included in the
scoring system and method disclosed herein. For example, the AV
access type and location can be included as risk factors. Patients
may be using either an AVF or an AVG access, and it may be
important to keep these types of accesses separate since they have
very different characteristics. AVG accesses tend to have more
complications than AVF accesses but are easier to repair, where AVF
accesses are less prone to complications but are harder to return
to patency. Access location may also have an impact on the results
and may be considered during interpretation. In addition, the
history of interventions to correct complications in the patient's
access can be included as a risk factor, as one or more prior
interventions may increase the risk of access complications going
forward. Additionally, other clinical variables such as age,
gender, body weight, blood pressure, diabetic status, etc. may be
associated with increased risk and can be included as risk factors.
The risk factors disclosed herein are not intended to be an
exhaustive list, and it is understood that other commonly collected
values are also contemplated.
[0027] Taken together, at least some of these variables can form
the basis of a system and method that prioritize the patients on an
alert list, and a scoring framework utilizing these variables can
predict patients who are at high risk for a thrombosis event or
requiring intervention. In this way, many variables can be combined
into a simple risk score that the patients, physicians and medical
staff can refer to as an indicator of risk, where the score should
correlate with the risk of a thrombosis and increase as the
vascular access becomes more occluded.
[0028] To develop the algorithm, time periods prior to a thrombotic
or documented intervention event were analyzed. In one example, 15,
30, 60, 90, and 120 days prior to an intervention can be selected.
As an example of a practical time period, approximately 15 days may
be required for staff to react to an indication of high risk and
have a reasonable chance of securing an intervention before the
thrombosis event. A 15-day time point also enables capturing data
for a patient that has a rapidly growing stenosis. Of course, other
time periods are also possible.
[0029] In one study, 985 patients (263 AVF; 722 AVG) were
identified, including 304 (81 AVF, 223 AVG) who experienced
vascular access thrombosis and 681 (182 AVF, 499 AVG) without
thrombosis, from 86 hemodialysis facilities with electronic
download of treatment and vascular access intervention data with up
to 120 days of treatment data per patient. Records were divided
into 15-day intervals (total intervals=7655; 2049 AVF and 5606 AVG)
and assessed to determine outcome (thrombosis vs. no thrombosis)
within the subsequent 60 days.
[0030] Sequential multivariant regression along with the use of
cubic splines that allows for non-linearity identified a plurality
of risk factors significantly associated (p<0.05) with access
thrombosis or an angioplasty intervention procedure in AVF and AVG
within 60 days: mean AAPR over 28 days, mean VAPR over 28 days
(severity), VAPR slope (change/28 days), number of VAPR alerts over
28 days (density), and the number of treatments where
delivered/prescribed blood flow rate <90% over 28 days
(adequacy). In one or more embodiments, each risk factor has a
possible raw score range based on the predictive value of the risk
factor for thrombosis or intervention. For example, score ranges
for an AVF could include 0-8 for mean AAPR, 0-8 for VAPR slope, 0-3
for treatment blood flow rates <90% prescribed, 0-2 for number
of VAPR alerts, and 0-12 for mean VAPR. Within the possible score
range for each risk factor, a raw score may be assigned for each
factor based on its value over a time period. The raw scores for
all of the risk factors may then be summed to obtain a cumulative
raw score. The cumulative raw score may be categorized based on the
type or location of the access (for example, an AVF in the upper
arm or the lower arm) or other factors. The resulting cumulative
raw score may then be associated with a level of risk, such as a
final risk score (for example, ranging from 1-10), where the higher
the number, the higher the risk of a thrombosis or
intervention.
[0031] FIG. 2 is a schematic illustration of data obtained during a
hemodialysis treatment session for a patient, wherein data for a
plurality of treatment sessions may be stored in a database. FIG. 3
is a schematic illustration of calculating risk factors such as
VAPR, AAPR, and blood flow rate from the hemodialysis treatment
data, and then evaluating these risk factors over time to
determine, for example, average VAPR, VAPR slope, number of VAPR
alerts, average AAPR, and blood flow rate <90% prescribed.
[0032] In one or more embodiments, a system associated with the
scoring method may include or be in communication with a detection
device, such as a hemodialysis machine, that is able to obtain
hemodialysis treatment data. The system may further include a
computer-driven analyzer or microprocessor arranged to receive
hemodialysis treatment data, such as from a hemodialysis machine,
during and after hemodialysis. In one or more embodiments, the
hemodialysis treatment data includes venous pressure (VP), arterial
pressure (AP), blood flow rate (BFR), and mean arterial pressure
(MAP). The computer-driven analyzer or microprocessor may include
an algorithm, wherein the algorithm may be used as part of an
integrated circuit. The algorithm may analyze the treatment data
over time to identify patients at risk for access dysfunction,
either for thrombosis or intervention, such as percutaneous
transluminal angioplasty or surgery to maintain access patency. The
system may also contain or be in communication with a computer
database to recall individual patient information and to store
hemodialysis treatment data in the patient's database record.
[0033] The findings from the regression models were used to assign
raw scores indicative of risk. In one analysis, using mean AAPR as
an example, intervals with a mean AAPR level for an AVF below 0.35
or above 0.525 were shown to be more likely to have a thrombosis or
an intervention within 60 days compared with those with a mean AAPR
between 0.35-0.525. Similar analyses were performed for each
parameter. Both low and high AAPR and VAPR slope, increasing or
decreasing, were shown to be associated with thrombosis or an
angioplasty intervention, as progressive stenosis produces an
increase or decrease in the observed intra-access pressure
depending on needle/lesion position.
[0034] The specific cut-offs between categories and raw scores
assigned were identified by considering the fit of the regression
models and the numbers of intervals falling into each category. Any
appropriate statistical modeling techniques could be applied to
create the score. As described above, all of the raw scores for
each of the five risk factors were added to arrive at a cumulative
raw score, from which a final risk score may be determined. The
probability of thrombosis or intervention was determined based on
the final risk score separately for AVF upper arm location, AVF
lower arm location, and AVG. For each access type/location, a
higher risk score (such as from 1-10) was strongly associated with
a higher probability of thrombosis or an intervention.
[0035] FIG. 4 is a chart illustrating the influence of vascular
access location on the final risk score. In particular, this chart
shows the percentage of the raw score that is associated with a
given final risk score. FIG. 5 is a chart depicting the probability
of any intervention and the proportion of the study patient
population by final risk score for AVF, and FIG. 6 is a chart
depicting the probability of any intervention and the proportion of
the study patient population by final risk score for AVG.
[0036] In one application of the scoring system and method, a total
of 18.9% treatments were associated with thrombosis or an
intervention for AVF in the subsequent 60 days. The cumulative
incidence of thrombosis was greater with higher cumulative score
(see table below). Scores 1-5 were associated with a relatively low
incidence of intervention (14.1% AVF, 25.7% AVG) and scores 6-10
with an increasing incidence of thrombosis or interventions in the
subsequent 60 days.
TABLE-US-00001 AVF AVG % of % of Treatments Treatments % of that
had an % that had an Risk Score Treatments Intervention Treatments
Intervention 1-5 60.2 14.1 63.4 25.7 6 15.0 22.1 12.6 33.1 7 10.6
25.9 9.5 36.0 8 7.5 29.3 7.9 38.7 9 4.8 31.2 4.6 41.5 10 1.9 38.2
2.1 43.2 Overall 100.0 18.9 100.0 29.7
[0037] Risk scores based upon the described scoring method
successfully identified vascular accesses with low or high
probability of developing access complications such as thrombosis
or having an intervention to treat significant stenosis within the
next 60 days. Because these scores are treatment-record based, they
may be easily augmented with pertinent clinical data and automated
to help guide vascular access patient care through a population
management approach.
[0038] Implicit in the design is the assumption that the change
between the values of a single measurement from one interval to the
next may be more useful than the measurements themselves.
Furthermore, a patient who presents with a persistently high VAPR
and therefore is always creating an alert may be at less risk for a
thrombosis event than a patient who has a VAPR slope that is
changing rapidly.
[0039] In one application of the system and method disclosed
herein, results for AVF (n=980,062 intervals) are shown in the
tables below. The events include the first occurrence of thrombosis
(n=9,814) or interventions (n=141,041). In this example, at least 4
measurements were required for each 15-day interval, participants
were dropped after a gap (missing or indaquate interval), no
allowance was made for prior interventions, and only the first
event was used. Of course, raw and final risk score scales used
herein are merely exemplary, and finer or courser scales could
alternatively be used. The tables below show the results for each
risk factor and the associated raw scores.
TABLE-US-00002 AVF VAPR Mean Value Points .ltoreq.0.25 0 >0.25 1
>0.30 2 >0.35 3 >0.40 4 >0.425 5 >0.45 6 >0.475 7
>0.50 8 >0.525 9 >0.55 10 >0.60 11 >0.65 12
TABLE-US-00003 AVF VAPR Slope Value Points -0.004-0.001 0 >0.001
1 >0.002 2 >0.004 3 >0.006 4 >0.008 5 >0.010 6
>0.0125 7 >0.015 8 <-0.004 1 <-0.006 2 <-0.008 3
<-0.010 4
TABLE-US-00004 AVF VAPR Alerts Value Points 0 0 1 6 2 12 3 18
.gtoreq.4 24
TABLE-US-00005 AVF AAPR Mean Value Points <0.35 1 =>0.35 to
=<0.525 0 >0.525 2 >0.55 4 >0.575 6 >0.60 8
TABLE-US-00006 AVF BFR <90% Value Points 0 0 1 1 =>2 3
The following table illustrates the conversion of the raw scores to
the final risk score for AVF:
TABLE-US-00007 Lower Arm Upper Arm Risk Score AVF AVF 1 0-1 0-1 2
2-3 2-3 3 4-5 4-5 4 6-7 6-7 5 8-14 8-9 6 15-25 10-20 7 26-33 21-30
8 34-39 31-36 9 40-43 37-40 10 .gtoreq.44 .gtoreq.41
The following table illustrates the percentage of treatments
included in each risk score and the percentage of 60-day intervals
that have an intervention:
TABLE-US-00008 AVF % of 60 Day % of Intervals that had Risk Score
Treatments an Intervention 1-5 60.2 14.1 6 15.0 22.1 7 10.6 25.9 8
7.5 29.3 9 4.8 31.2 10 1.9 38.2 Overall 100.0 18.9
[0040] FIG. 7 is a graph showing the relative risk of complication
as a function of VAPR slope for an AVF, where the greater the slope
upward (right of center) or downward (left of center) indicates
increasing risk of thrombosis or an intervention.
[0041] Results for AVG (n=477,925 intervals) are shown in the
tables below. The events include the first occurrence of thrombosis
(n=40,176) or interventions (n=126,295). In this example, at least
4 measurements were required for each 15-day interval, participants
were dropped after a gap (missing or indaquate interval), no
allowance was made for prior interventions, and only the first
event was used. Again, raw and final score scales used herein are
merely exemplary, and finer or courser scales could alternatively
be used.
TABLE-US-00009 AVG VAPR Mean Value Points .ltoreq.0.40 0 >0.40 1
>0.45 2 >0.50 3 >0.55 4 >0.60 5 >0.65 6 >0.70 7
>0.80 8 .gtoreq.0.90 9
TABLE-US-00010 AVG VAPR Alerts Value Points 0 0 1 2 2 4 3 6
.gtoreq.4 8
TABLE-US-00011 AVG VAPR Slope Value Points -0.005-0.001 0 >0.001
2 >0.002 4 >0.004 6 >0.005 8 >0.008 10 >0.010 12
>0.0125 14 >0.015 16 <-0.005 2 <-0.010 4 <-0.015
6
TABLE-US-00012 AVG AAPR Mean Value Points .ltoreq.0.40 0 >0.40 2
>0.45 4 >0.475 6 >0.50 8 >0.55 10
TABLE-US-00013 AVG BFR <90% Value Points 0 0 1 1 2 2 .gtoreq.3
3
The following table illustrates the conversion of the raw scores to
the final risk score for AVG:
TABLE-US-00014 Risk Score AVG 1 0-3 2 4-5 3 6-8 4 9-10 5 11-14 6
15-17 7 18-20 8 21-24 9 25-29 10 .gtoreq.30
The following table illustrates the percentage of treatments
included in each risk score and the percentage of 60-day intervals
that have an intervention:
TABLE-US-00015 AVG % of 60 Day Intervals % that had an Risk Score
Treatments Intervention 1-5 63.4 25.7 6 12.6 33.1 7 9.5 36.0 8 7.9
38.7 9 4.6 41.5 10 2.1 43.2 Overall 100.0 29.7
[0042] A similar scoring system and method can be envisioned for
other medical surveillance systems including a scoring algorithm
designed to indicate the potential risk for a hemodialysis patient
to have a hypotensive episode during a hemodialysis treatment.
[0043] As an example of another scoring application, FIG. 8 shows
data that can obtained during a patient's hemodialysis treatment
which includes periodic blood pressure measurements BP (1),
systolic pressure, diastolic pressure, pulse rate (2) and mean
arterial pressure (3). Other important parameters recorded during
hemodialysis include blood flow rate (4), venous return pressure VP
(5), negative arterial pressure created by the blood pump,
ultrafiltration rate (6), change in the relative circulating blood
volume, time on dialysis, and blood oxygen saturation.
[0044] Several parameters can be continuously calculated during the
hemodialysis treatment including the rate of change in the
circulating blood volume, the blood pressure in the patent's
dialysis access site (VAPR), referred to as access pressure (7),
the moving average of access pressure (8) and the rate of change
(slope) of the access pressure, where the shaded box (9) shows
rapid decrease in slope of the access pressure that correlates with
a documented hypotensive episode.
[0045] Other factors from the patient's medical history can be
included in the scoring to determine the risk of a hypotensive
event during hemodialysis. Patient history parameters include the
total number previous hypotensive events during hemodialysis, the
date of the last hypotensive event, the frequency of hypotensive
events during hemodialysis, patient medications and any specific
symptoms of cardiovascular disease. The patient's medical history
can be given an overall score or individual scores that can
accessed by the dialysis computer monitoring the patient in real
time during the hemodialysis treatment.
[0046] FIG. 9 depicts an example of an actual patient's vascular
access pressure and blood flow results showing the vascular access
score over time. The top bar graph is the calculated score at the
end of each month. The next lower graph is the VAPR over time,
where the vertical bars represent the venous intra-access pressure
calculated for each session. The dotted horizontal line is the
high-pressure threshold, the darker vertical lines are calculated
venous alerts, and the solid trace spanning the date axis is the
running average of the venous intra-access pressure. The issues
illustrated for VAPR are an upward and then a downward slope, a
high average pressure, and a lot of alerts (darker vertical lines).
The next graph below is AAPR, with the vertical lines indicating
the calculated arterial intra-access pressure for each session. The
downward slope of AAPR is indicative of growing problems. The
bottom graph is hemodialysis blood flow rate (BFR) over time. The
horizontal line is the prescribed blood flow, the lighter vertical
lines are the average blood flow for each session, and the darker
vertical lines indicate that that session did not achieve at least
90% of prescribed blood flow. The fact that an angioplasty was
performed is evidence that there was a significant stenosis to
correct.
[0047] Another application of the scoring method in vascular access
care is to monitor catheters for changes in multiple
characteristics, which can decrease the effectiveness of the
hemodialysis session. For example, changes in the normalized
arterial and/or venous pressure, changes in the blood viscosity
(Hct) and other indicators may signal impediments or changes to the
ability of blood to flow through the catheter. A reduction in blood
flow through a catheter might indicate the growth of a fibrin
sheath over time. This will impact the success of hemodialysis
treatment and may result in the catheter requiring additional
medical procedures to maintain proper function.
[0048] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
invention. Rather, the words used in the specification are words of
description rather than limitation, and it is understood that
various changes may be made without departing from the spirit and
scope of the invention. Additionally, the features of various
implementing embodiments may be combined to form further
embodiments of the invention.
* * * * *