Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR DISPLAYING MEDICAL PROCESS DIAGRAMS
Field of the Invention
This invention relates to display systems. More specifically, this invention
relates to systems for displaying
graphical information, particularly in a medical setting.
Background of the Invention
Medical display systems provide information to doctors in a clinical setting.
Typical display systems provide data
in the form of numbers and one-dimensional signal waveforms that must be
assessed, in real time, by the attending
physician. Alarms are sometimes included with such systems to warn the
physician of an unsafe condition, e.g., a number
exceeds a recommended value. In the field of anesthesiology, for example, the
anesthesiologist must monitor the patient's
condition and at the same time Ii) recognize problems, (ii) identify the cause
of the problems, and (iii) take corrective action
during the administration of the anesthesia. An error in judgment can be
fatal.
Approximately 50 percent of the more than 2000 anesthesia-related deaths per
year have been found to be due
to improper choices during surgery. In general, human error in anesthesia
represents failure by the anesthesiologist to
recognize a problem labnormal physiology), identify the cause of the problem
and take appropriate corrective action when
administering an anesthetic to a patient. Anesthesia performance models,
models showing the relationship between
errors, incidents and accidents, and models depicting accident evolution in
the anesthesia all illustrate the fact that
anesthesia is a complex environment prone to errors.
Physiologic data displays of the patient's condition play a central role in
allowing anesthesiologists to observe
problem states in their patients and deduce the most likely causes of the
problem state during surgery. As one might
predict, 63 percent of the reported incidents in the Australian Incident
Monitoring Study (AIMS) database were considered
detectable with standard data monitors. Others have attempted to address these
problems, but with only limited success.
For example, Cole, et. al. has developed a set of objects to display the
respiratory physiology of intensive care
unit (ICU) patients on ventilators. This set of displays integrates
information from the patient, the ventilator, rate of
breathing, volume of breathing, and percent oxygen inspired. Using information
from object displays, ICU physicians made
faster and more accurate interpretations of data than when they used
alphanumeric displays. Cole published one study
that compared how physicians performed data interpretation using tabular data
vs. printed graphical data. However,
Cole's work did not involve a system for receiving analog data channels and
driving a real-time graphical display on a
medical mon'ttor.
In addition, Ohmeda, a company that makes anesthesia machines, manufacturers
the Moduius CD machine which
has an option for displaying data in a graphical way. The display has been
referred to as a glyph. Physiologic data is
mapped onto the shape of a hexagon. Six data channels generate the six sides
of the hexagon. Although this display is
graphical, the alphanumeric information of the display predominates. There is
no obvious rational for why the physiologic
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data is assigned a side of the hexagon. Moreover, symmetric changes to the
different signs of this geometric shape are
very hard for individuals to differentiate.
In the surgical and postoperative settings, decisions regarding the need for
blood transfusion normally are guided by
hemoglobin (Hb) or hematocrit levels (Hct). Hematocrit is typically defined as
the percentage by volume of packed red blood
cells following centrifugation of a bbod sample. If the hemoglobin level per
deciliter of blood in the patient is high, the physician
can infer that the patient has sufficient capacity to carry oxygen to the
tissue. During an operation this value is often used as a
trigger; i.e. if the value falls below a certain point, additional blood is
given to the patient. While these parameters provide an
indication of the arterial oxygen content of the blood, they provide no
information on the total amount of oxygen transported (or
"offered") to the tissues, or on the oxygen content of blood coming from the
tissues.
For example, it has been shown that low postoperative hematocrit may be
associated with postoperative ischemia in
patients with generalized atherosclerosis. Though a number of researchers have
attempted to define a critical Hct level, most
authorities would agree that an empirical automatic transfusion trigger,
whether based on Hb or Hct, should be avoided and that
red cell transfusions should be tailored to the individual patient. The
transfusion trigger, therefore, should be activated by the
patient's own response to anemia rather than any predetermined value.
This is, in part, due to the fact that a number of parameters are important in
determining how well the patient's
tissues are actually oxygenated. In this regard, the patient's cardiac output
is also an important factor in correlating
hemoglobin levels with tissue oxygenation states. Cardiac output or CO is
defined as the volume of blood ejected by the left
ventricle of the heart into the aorta per unit of time (mllmin) and can be
measured with thermod~lution techniques. For example,
if a patient has internal bleeding, the concentration of hemoglobin in the
blood might be normal, but the total volume of blood
will be low. Accordingly, s'mply measuring the amount of hemoglobin in the
blood without measuring other parameters such as
cardiac output is not always sufficier~ for estimating the actual oxygenation
state of the patient.
More specifically the oxygenation status of the tissues is reflected by the
oxygen supplyldemand relationship of those
tissues i.e., the relationship of total oxygen transport (DOZ) to total oxygen
consumption NOZI. Hemoglobin is oxygenated to
oxyhemoglobin in the pulmonary capillaries and then carried by the cardiac
output to the tissues, where the oxygen is
consumed. As oxyhemoglobin releases oxygen to the tissues, the partial
pressure of oxygen (POZ) decreases until sufficient
oxygen has been released to meet the oxygen consumption NOz). Although there
have been advances in methods of
determining the oxygenation status of certain organ beds (e.g., gut tonometry;
near infrared spectroscopy) these methods are
difficuh to apply in the clinical setting. Therefore, the use of parameters
that reflect the oxygenation status of the blood
coming from the tissues i.e., the partial pressure of oxygen in the mixed
venous blood (PvOZ; also known as the mixed venous
blood oxygen tension) or mixed venous blood oxyhemoglobin saturation (SvOz)
has become a generally accepted practice for
evaluating the global oxygenation status of the tissues.
Unfortunately, relatively invasive techniques are necessary to provide more
accurate tissue oxygenation levels. In this
respect, direct measurement of the oxygenation state of a patient's mixed
venous blood during surgery may be made using
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puknonary artery catheterization. To fully assess whole body oxygen transport
and delivery, one catheter (a flow directed
pulmonary artery [PA] catheter) is placed in the patient's pulmonary artery
and another in a peripheral artery. Blood samples
are then drawn from each catheter to determine the pulmonary artery and
arterial blood oxygen levels. As previously ~scussed,
cardiac output may also be determined using the PA catheter. The physician
then infers how well the patient's tissue is
oxygenated directly from the measured oxygen content of the blood samples.
While these procedures have proven to be relatively accurate, they are also
extremely invasive. For example, use of
devices such as the Swan-Ganz~ thermodilution catheter (Baxter International,
Santa Ana, CA) can lead to an increased risk of
infection, pulmonary artery bleeding, pneumothorax and other complications.
Further, because of the risk and cost associated
with PA catheters, their use in surgical patients is restricted to high-risk
or high-blood-loss procedures (e.g., cardiac surgery,
liver transplant, radical surgery for malignancies) and high-risk patients
(e.g., patients who are elderly, diabetic, or have
atherosclerotic disease).
Among other variables, determination of the oxygenation status of the tissues
should include assessment of the
amount of blood being pumped toward the tissues (C0) and the oxygen content of
that (arterial) blood (Ca02). The product of
these variables may then be used to provide a measure of total oxygen
transport (DOz). Currently, assessment of D02 requires
the use of the invasive monitoring equipment described above. Accordingly,
determination of DOZ is not possible in the majority
of surgical cases. However, in the intensive care unit (ICUI, invasive
monitoring tends to be a part of the routine management
of patients; thus, DOZ determinations are obtained more readily in this
population.
Partial pressure of oxygen in the mixed venous blood or mixed venous blood
oxygen tension (PvOZ) is another
important parameter that may be determined using a PA catheter. Because of the
equilibrium that exists between the partial
pressure of oxygen (POZ) in the venous blood and tissue, a physician can infer
the tissue oxygenation state of the patient. More
specifically, as arterial blood passes through the tissues, a partial pressure
gradient exists between the POZ of the blood in the
arteriole passing through the tissue and the tissue itself. Due to this oxygen
pressure gradient, oxygen is released from
hemoglobin in the red blood cells and also from solution in the plasma; the
released OZ then diffuses into the tissue. The POZ of
the blood issuing from the venous end of the capillary cylinder (Pv02) will
generally be a close reflection of the P02 at the distal
(venous) end of the tissue through which the capillary passes.
Closely related to the mixed venous blood oxygen tension (Pv02) is the mixed
venous blood oxyhemoglobin saturation
(Sv02) which is expressed as the percentage of the available hemoglobin bound
to oxygen. Typically, oxyhemoglobin
disassociation curves are plotted using S02 values vs. POZ values. As the
partial pressure of oxygen (POZ) decreases in the
blood (i.e. as it goes through a capiuary) there is a corresponding decrease
in the oxygen saturation of hemoglobin (SOZ). While
arterial values of P02 and S0z are in the neighborhood of 95 mm Hg and 97%
respectively, mixed venous oxygen values (Pv02,
SvOz) are on the order of 45 mm Hg and 75% respectively. As such SvOZ, like
PvOz, is indicative of the global tissue
oxygenation status. Unfortunately, like PvOz, -tt is only measurable using
relatively invasive measures.
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Another rather informative parameter with respect to patient oxygenation is
deliverable oxygen (dD02). dDOz is the
amount of the oxygen transported to the tissues (DOz) that is able to be
delivered to the tissues (i.e. consumed by the tissues)
before the Pv02 (and by implication the global tissue oxygen tension) fads
below a certain value. For instance the dD02140) is
the amount of oxygen that can be delivered to the tissues (consumed by the
tissues) before Pv02 is 40 mm Hg while dD02(35) is
the amount consumed before the Pv02 falls to 35 mm Hg.)
Additional relevant parameters may be determined non-invasively. For instance,
whole body oxygen consumption
(VOi) can be calculated from the difference between inspired and mixed expired
oxygen and the minute volume of ventilation.
Cardiac output may also be non-invasively inferred by measuring arterial blood
pressure instead of relying on thermocklution
catheters. For example, Kraiden et al. (U.S. Patent No. 5,183,051,
incorporated herein by reference) use a blood pressure
monitor to continuously measure arterial blood pressure. These data are then
converted into a pulse contour curve waveform.
From this waveform, Kraiden et al. calculate the patient's car~ac output.
Regardless of how individual parameters are obtained, those skilled in the art
will appreciate that various well
established relationships allow additional parameters to be derived. For
instance, the Fick equation (Fick, A. Wurzburg,
Phvsikalisch edizinische Gesellschaft Sitzungsbericht 16 (18701) relates the
arterial oxygen concentration, venous oxygen
concentration and cardiac output to the total oxygen consumption of a patient
and can be written as:
(Ca02 - CvOZ1 x CO - VOz
where Ca02 is the arterial oxygen content, CvOz is the venous oxygen content,
CO is the cardiac output and VOZ represents
whole body oxygen consumption.
While the non-invasive derivation of such parameters is helpful in the
clinical setting, a more determinative
"transfusion trigger" would clearly be beneficial. If PvOZ or DOZ is accepted
as a reasonable indicator of patient safety, the
question of what constitutes a "safe" level of these parameters arises. Though
data exists on critical oxygen delivery levels in
animal models, there is little to indicate what a critical PvOz might be in
the clinical situation. The available data indicate that
the level is extremely variable. For instance, in patients about to undergo
cardiopulmonary bypass, critical Pv02 varied between
about 30 mm Hg and 45 mm Hg where the latter value is well within the range of
values found in normal, fit patients. Safe DOz
values exhibit similar variabg'tty.
For practical purposes a PvOZ value of 35 mm Hg or more may be considered to
indicate that overall tissue oxygen
supply is adequate. but this is implicit on the assumption of an intact and
functioning vasomotor system. Similarly, the accurate
determination of DOZ depends on an intact circ~datory system. During surgery
it is necessary to maintain a wide margin of
safety and probably best to pick a transfusion trigger (whether D02, Pv02,
SvOz or some derivation thereof) at which the patient
is obviously in good condition as far as oxygen dynamics are concerned. In
practice, only certain patients will be monitored with
a pulmonary artery catheter. Accordingly, the above parameters wilt not be
available for all patients leaving the majority to be
monitored with the knperfect, and often dangerous, trigger of Hb
concentration.
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Efforts to resolve these problems in the past have not proven entirely
successful. For example, Faithfull et al. Ox en
Transport to Tissue X111. Ed. M. Hogan, Plenum Press, 1994, pp. 41-49)
describe a model to derive the oxygenation status of
tissue under various cond'ttions. However, the model is merely a static
simulation allowing an operator to gauge what effect
changing various cardiovascular or physical parameters will have on tissue
oxygenation. No provisions are made for continuous
S data acquisition and evaluation to provide a dynamic representation of what
may actually be occurring. Accordingly, the model
cannot be used to provide real-time measurements of a patient's tissue
oxygenation under changing clinical conditions.
Thus, what is needed in the art is a means for intuitively displaying
physiological information to a physician. In
this respect the methods and systems described below provide novel approaches
to improve a physician's interpretation of
patient data. Other aspects of the invention will become apparent in the
description that follows.
Summary of the Invention:
Embodiments of the invention provide for the determination and display of one
or more values that accurately reflect
the physiological condition of a patient. Preferred values include the global
oxygenation and cardiovascular status of the
patient. Each of these values can be displayed as intuitive medical process
diagrams to assist the physician in understanding
the medical condition of their patient. Moreover, many of the displayed values
can be advantageously determined without
invasive procedures on the patient. As such, the display system and methods
discussed herein may be used to safely and
intuitively monitor the physiological condition of patients and adjust
therapeutic parameters based on the displayed values.
It will be appreciated that the display systems of the present invention may
be used in conjunction with a wide
variety of medical instrumentation to provide the des'ned physiological
information. More particularly, the disclosed displays
may be operably associated with any instrumentation or device that is used to
monitor or treat a patient. In this respect such
instrumentation includes, but is not limited to, anesthesia machines,
ventilators, heart-lung machines and oxygenation monitors
of the type described herein. Exemplary display values may be oxygenation
parameters or analogous information in the case of
anesthesia machines, ventgators or oxygenation monitors or cardiodynamic
information in the case of heart-lung machines. In
any event, the disclosed displays provide for the effective presentation of
quantitative data in a manner that allows for rapid
comprehension by the care giver.
fn preferred embodiments, the preserrr invention provides for the
determination and real-time display of physiologically
important oxygenation parameters int6cative of a patient's tissue oxygenation
status such as, for example, total oxygen
transport (D02), deliverable oxygen transport (dD021, mixed venous blood
oxyh~noglobin saturation (SvOz) and mixed venous
blood oxygen tension (PvOz). The invention may also be used to provide a
supply(demand ratio (dDO2N0z), another oxygenation
parameter, that allows a physician to accurately monitor and adjust the oxygen
status of a patient using a single numerical
value.
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It will be appreciated that the derived oxygenation parameters may be used
alone or, more preferably, in combination
to provide an indication as to global tissue oxygenation levels. As such, the
invention may be used as an uncomplicated, real-
time intervention tt~gger in clinical settings w'tthout the risks associated
with conventional invasive mon'ttoring equipment.
Mare specifically, by establishing the minimum acceptable Pv02, Sv02, dDOZ or
DOZ for the individual patient, the
S attending physician is provided with a simple trigger point where
intervention is indicated. For example, based on clinical
experience, a physician may determine that the PvOz of a patient should not be
below 35 mm Hg or that the DOZ should remain
above 600 mllmin in order to provide adequate oxygenation. (Preferably, the
clinician will have access to each of the
oxygenation parameters and can d'~splay one or more values as desired. In a
particularly preferred embodiment, the system will
provide a supplyJd~nand ratio (dD02N02) for a selected PvOZ thereby allowing
the physician to address the needs of the patient
based on a single value. In this embodiment, a value of one or greater
indicates the Pv02 (and hence global tissue oxygenation)
is higher than the estabbshed trigger poim.
Particularly preferred embodiments provide a continuous (beat-to-beat)
measurement of cardiac output (C01, using
inputs from an indwelling catheter placed in a peripheral artery. In this
respect an apparatus such as the Modelflow system
(TNO-Biomedical Instrumentation, Amsterdam), can optionally be used in
conjunction with the present invention to provide the
CO measuremerrt continuously in real-time. Cardiac output may be computed
using an algorithm that simulates the behavior of
the human aorta and arterial system via a three-element, nonlinear model of
aortic input impedance. Cardiac output computed
using this model has been validated against cardiac output determined by
thermodilution. In addition to cardiac output, the
following hemodynamic information can be derived from systems like Modelflow
on a beat-to-beat basis: systolic, diastolic, and
mean arterial pressure; pulse rate; stroke volume; and peripheral vascular
resistance.
Embodiments of the invention also determine the arterial oxygen content (Ca02)
of the patient for use in deriving the
desired values. Specifically, in determining the arterial oxygen content
(CaOz), one or more numerical values may be used
corresponding to the patient's hemoglobin concentration, arterial oxygen
tension (Pa0zl, arterial carbon dioxide tension (PaC0zl,
arterial pH and body temperature. These numerical values may be obtained from
a blood chemistry monitor or entered
manually. Particularly preferred embodiments employ a blood chemistry monitor
to obtain the desired values
contemporaneously with the measurement of the cardiac output values.
Additionally, the oxygen consumption of the patient
(VOZ) is determined, preferably by gas analysis or metabolic rate
determination.
As previously indicated, the embodanents of the invention further provide
methods and apparatus that may be used to
mon'ttor the tissue oxygenation status of a patient using a supplyldemand
ratio. Accordingly, one embodiment of the invention
is directed to a relatively non-invasive method for monitoring, in real-time,
tissue oxygenation status of a patient comprising the
determination of a supplyldemand ratio (dDOZN021. Sim~arly, another embodiment
is directed to a relatively non-invasive
apparatus for determining, in real-time, tissue oxygenation status of a
patient. The apparatus may include instructions for
determining a supplyldemand ratio (dDO~NOzI. The calculations, values and
equipment necessary to provide the desired ratios
are as described throughout the present specification.
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In all cases it must be emphasized that, while preferred embodiments of the
invention include a blood chemistry
monitor andlor pressure transducers (i.e. for C01, they are not essential
components of the present invention and are not
necessary for practicing the disclosed methods. For example, a physician could
manually measure blood gas levels, body
temperatures and Hg concentrations and then enter this information into the
system via the keyboard. Other methods of
measuring cardiac output could be used, such as uhrasound, thoracic impedance,
or partial C02 rebreathing method.
Those skilled in the art wig further appreciate that oxygenation constants are
numerical values primarily related to the
physical characteristics of oxygen carriers or to the physiological
characteristics of the patient. Such oxygenation constants
inctude, but are not limited to, blood volume, oxygen solubility in plasma and
the oxygen content of a desired unit of saturated
oxyhemoglobin. Preferably, one or more oxygenation constants is used in the
present invention to derive the selected
oxygenation parameters.
From the values obtained using oxygenation constants Ifor example CaOz, V02
and CO), the present invention solves
the Fick equation [VOZ - ICaOz - CvOz) x CO] by calculating the mixed venous
blood oxygen content ICv02) of the patient. Once
the CvOz has been determined, Sv02 can be calculated and the PvOZ can be
readily be derived using algorithms for calculating
the position of the oxyhemoglobin disassociation curve such as the Kelman
equations (Keknan, J. Aanl. Phvsiol, 1966, 2114):
1375-1376; incorporated herein by reference). Similarly, other parameters such
as D02, dD02 and dD02N02 may be derived
from the obtained values.
Using the methods disclosed herein, an anesthesiologist could cor~inuously
receive real-time data (i.e., the
oxygenation parameters discussed above), thereby revealing a complete picture
of the patient's global oxygenation status.
Should arry of the selected parameters approach the established trigger
points, appropriate actions such as pharmacological
intervention, fluid loading, blood transfusion or adjustment of the
ventilation profile could be undertaken in plenty of time to
stabilize the subject. Thus, this cominuous flow of data would allow the
physician to more readily determine the etiology of the
oxygenation decrease (such as, but not gm'tted to, anemia, decreased cardiac
output or hypoxia) and tailor the response
appropriately.
Aspects of the invention focus on the graphical display of data to users in
high-risk environments (such as
medicine) to reduce possible human error. In particular, the systems and
displays of the invention serve to map the
operator's cognitive needs into the graphical elements of the display. In
certain aspects, therefore, the invention mimics
body physiology so that display data better represents patient data and body
function.
fn one aspect, the invention utilizes task-analysis methodology to transform
data into information and display
oxygen-transport physiological data. The physician is able to see information
(not raw data) to interpret this data - with
fewer errors as compared to like interpretation of data generated by other
systems - to diagnose pathological states and
to take appropriate corrective action. In certain aspects, the invention thus
generates a set of informative object displays
from one, two or more sensors collecting data from the patient. These object
displays can show, for example, (1) the
relationships of data relative to other data; (2) data in context; (3) a frame
of reference for the data; (4) the rate of change
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of information for the data; andlor (5) event information. A system
constructed according to the invention is thus
particularly advantageous in presenting oxygen-transport physiology to
doctors.
In another aspect of the invention, the system utilizes data acquisition
hardware (e.g., patient probes), a
computer, and object display algorithms and software. In one preferred aspect,
the software and algorithms use digital
representations of analog data channels (dernred, for example, from patient
monitoring signals and probes) to construct a
set of object displays representing oxygen-transport physiology. However, it
should be noted that aspects of the invention
related to the intuitive medical process ~agrams of oxygen-transport
physiology do not require any particular monitoring
equipment. Any type of well-known patient monitoring devices could be used for
gathering data that is thereafter displayed as
an intuitive medical process diagram.
The invention provides several advantages over the prior art. By way of
example, data displays of the invention
map patient information into meaningful mental models. Doctors using such
mental models are thus better able to
understand complex physiology such as oxygen-transport physiology. In certain
aspects, the mental models come in the
form of analogies for portraying complex processes. One suitable oxygen-
transport physiology model of the invention thus
includes: (1) the loading of fuel in the form of oxygen onto red blood cells
at the lungs; (2) the pumping of oxygenated blood
by the heart to organs and tissues; (3) the unloading of oxygen from red blood
cells to tissues; and (4) the utilization of the
oxygen by organs and tissues.
By analogy, one might compare this model to: (1) the loading of fuel in the
form of coal into train box cars at a
coal yard; (2) the transport of these loaded box cars by the train's
locomotive to a furnace some distance away; (3) the
unloading of coal from the box cars to the furnace; and (4) the burning of the
coal by the furnace. In this analogy, the coal
yard represents the lungs which are inflated with oxygen. The train's box cars
represent the red blood cells which are
loaded with oxygen. The locomotive represents the heart pumping red blood
cells carrying oxygen around a circulatory
track between the lungs and the tissues. The percent of each box car's coal
which is dumped at the furnace is
representative of the fractional extraction of oxygen by cells within tissues.
Finally, the burning coal in the furnace
represents oxygen utilization by cells and tissues.
As previously indicated, the present invention is compatible with a number of
different types of medical
instrumentation. Similarly, aspects of the invention can be used in several
settings. First, the system can be used with
sensor sets from different manufacturers, which drive the data display. As for
the display of objects, the display can be
used in part, or in its entirety. Example medical domains where all or part of
oxygen transport physiology can be monitored
include: the intensive care unit, the operating room, the emergency room, and
all procedure rooms. The display system of
the invention can also be used to present oxygen-transport physiology
information to the medical care team while patients
are on cardiopulmonary bypass. The system can also be attached to medical
simulation devices, e.g., a surgical dummy,
for education and training of personnel regarding oxygen-transport physiology.
_g_
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The software of the invention can be installed on medical devices currently
used in data acquisition, particularly
those used in connection with oxygen-transport physiology or cardiodynamics.
The invention can also be used to monitor
oxygen-transport physiology for veterinary medicine, or to monitor oxygen-
transport physiology in animal laboratories.
In certain aspects, the invention can be a module which interacts with other
displays of physiology, such as
respiratory physiology. It can also be used to implement research protocols
which allow better execution of complex
control tasks. Further use can include an interface for analyzing large data
sets of oxygen-transport information.
One embodiment of the invention is a method for displaying physiologic data
from a patient. In this embodiment,
data is measured by way of a probe or other device from an organ in a patient.
The measured data is then used to
determine a physiologic quantity relating to the data, such as the blood
oxygenation level or cardiodynamic values in the
patient. The physiologic quantity is then displayed as an object, wherein the
shape of the displayed object reflects the
structure of the organ.
Another embodiment of the invention is a method for displaying physiologic
data from a patient. In this
embodiment, the blood oxygenation levels of a patient are first measured by
conventional means. A circular shape is then
displayed, wherein the circular shape is shaded to represent the percentage of
the patient's blood that is oxygenated.
Yet another aspect of the invention is a method for displaying physiologic
data from a patient, wherein the blood
oxygenation levels in a patient are first measured through conventional
methods. A plurality of shapes are then displayed
on a monitor, wherein each of the plurality of shapes represents the structure
of an organ in the human body.
One additional embodiment of the invention is a method for displaying
physiologic data from a patient, wherein
analog gauges, such as dials or needles are used to represent the physiologic
data.
Another aspect of the invention is a display system for representing
physiologic data from a patient. The display
system includes a set of display objects, with each object representing a
different, but related measurement taken from
the patient. An integrated display may be formed from a set of four objects.
The first object represents the patient's
cardiac output, the second object represents the patient's arterial blood
oxygenation levels, the third object represents the
patient's venous blood oxygenation levels, and the fourth abject represents
the tone of the patient's arteries, capillaries,
and veins.
The invention is next described further in connection with preferred
embodiments, and it will become apparent
that various additions, subtractions, and modifications can be made by those
skilled in the art without departing from the
scope of the invention.
Brief Description of the Drawings:
FIGURE 1 is a schematic diagram illustrating one system constructed according
to embodiments of the invention
for collecting, processing and displaying oxygen transport physiology.
FIGURE 2 is a schematic diagram of a computer system that may be used to run
the present invention.
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CA 02321227 2000-08-24
ee ever rr . r
. r r r r . r r r
FIGURE 3 is a flowchart detailing a preferred software schemie~ fh~t may ~e
p~ed rto~ rug the ~resedtr,r r' r:
a er r rr r, .r ..
invention.
FIGURE 4 is a schematic diagram of data input and calculations as performed in
selected embodiments of
the present invention.
FIGURE 5 illustrates one embodiment of a red blood cell object.
FIGURE 6 is a flowchart illustrating one method for updating a display of the
red blood cell object from
Figure 5.
FIGURE 7 illustrates one embodiment of a heart pump object.
FIGURE 8 is a flowchart illustrating one method for updating a display of the
heart pump object from Figure
7.
FIGURE 9 illustrates one embodiment of a vascular resistor object.
FIGURE 10 is a flowchart illustrating one method for updating a display of the
vascular resistor object from
Figure 9.
1
FIGURE 11 illustrates one embodiment of a metabolism object.
FIGURE 12 is a flowchart illustrating one method far updating a display of the
metabolism object from
Figure 11.
FIGURE 13 illustrates a display representing a circuit for displaying
physiological data. In one embodiment,
the display includes a heart pump object, vascular resistor object, red blood
cell object and metabolism object.
FIGURE 14 iAustrates selected object displays and elements that are compatible
with the present invention.
More particularly, Fig. 14A shows an alveolar-arterial partial pressure oxygen
gradient object, Fig. 14B shows a data
box graphical element and Fig. 14C shows an acid-base graph object.
Detailed Description of the Preferred Embodiments: -
The present invention relates to methods and systems for obtaining medical
information from patients and
j 25 then displaying that information in an intuitive format to a physician.
The intuitive format may be termed a medical
i
process diagram because physicians reading the displayed information can
quickly perceive the importance of changing
patient values. Medical process diagrams have been developed by others in non-
anesthesia domains to take advantage
of advancements in cognitive research.
Research in applied human factors has focused on using graphical displays in
high-risk environments similar
to the operating room ~e.g., nuclear power control rooms and airplane flight
decks) to reduce human error. The
success of medical process diagrams appears to be a function of how well the
semantics of the operator's cognitive
needs are mapped into the graphical elements of the display. Using accepted
task-analysis methods, a system was
developed describing how medical doctors interpret oxygen-transport
physiological data to diagnose pathological
states and
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WO 99/39633 PCTNS99/02798
subsequently take appropriate corrective action in their patients. In an
effort to make the many data that doctors need to
interpret more informative, a set of object displays was developed.
The set of display objects was developed to illustrate: 1 ) the relationships
of data to other data; 2) data in
context; 3) a frame of reference for the data; 4) the rate of change
information for the data; and 5) event information.
Specifically, a system was developed for presenting oxygen-transport
physiology to doctors. The system uses data
acquisition hardware, a computer, oxygen transport calculation software and
object display software. In one embodiment,
as discussed in detail below, the object display software uses data provided
by oxygen transport calculation software to
construct a set of four objects representing oxygen-transport physiology.
Unfortunately, current display systems that present physiologic data to
physicians in critical care force the
physicians to perform a great deal of cognitive work to interpret that data.
In contrast, the display system described
below utilizes visual memory cues and perceptual diagrams to map complex data
graphically. These data maps are then
displayed to match the mental model physicians use to interpret oxygen-
transport physiology. Because the system
receives analog signals from the patient and thereafter calculates several
physiological quantities, patient data is used to
drive the display in real-time.
As discussed above, the present invention may be used or associated with a
variety of medical instruments
including ventilators, anesthesia machines, partial or total liquid
ventilation systems, cardiodynamic monitors and heart-
lung machines. More generally, the present invention may be used in concert
with any computerized laboratory
information system such as may be found in an operating room or intensive care
unit. In preferred embodiments, the
parameters or values to be displayed will be derived by one or more
instruments and communicated to a centralized display
(i.e., a video monitor). In other embodiments the devices may operate as stand
alone systems with a built in display.
Either way, the operator will preferably be able to manipulate the display
parameters so as to optimize the presentation of
the desired data. It will then be appreciated that the operator can adjust the
appropriate devices based on the displayed
data.
With regard to ventilators, the displays are compatible with several systems
in current use. Either volume
regulated, time-cycled respirators or pressure-limited time-cycled respirators
are suitable. As previously alluded to,
conventional ventilators such as these may be used with the present invention
in conjunction with traditional gas
ventilation or with partial liquid ventilation. Similarly, the present
invention may be used in conjunction with a wide variety
of commercially available cardiopulmonary bypass machines or blood oxygen and
hemoglobin monitoring equipment (i.e.
pulmonary catheters, EKGs, etc.l. In other preferred embodiments the displays
of the present invention may be driven by
commercially available integrated anesthesia delivery and monitoring units. In
yet other embodiments the graphical
displays may be used in concert with closed-circuit liquid ventilation systems
such as those described in WO 97119719
which is incorporated herein in its entirety. Regardless of which type of
medical system is selected, those skilled in the art
will appreciate that the present invention allows for the intuitive display of
the relevant parameters. As evidenced by
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WO 99/39633 PCTNS99/02798
the foregoing, the displays of the present invention are compatible with
several types of medical instrumentation.
However, for the purpose of explanation the following discussion will examine
the display of oxygenation parameters in
conjunction with a novel real-time oxygenation analyzer. In that the following
description of the present invention discloses
only exemplary embodiments thereof, it is to be understood that other
variations are co~emplated as being within the scope of
the present invention. Accordingly, the present invention is not limited to
the particular embodiments which are described in
detail below.
I. Hardware System
Figure 1 illustrates a system 10 constructed according to an embodiment of the
invention directed to the
determination of oxygenation parameters. A series of probes 12 are connected
to various monitoring activities associated
with the patient 14, e.g., a heart rate probe 12a. These probes are well known
and typically generate analog signals 16
representative of the monitored activity. The signals 16 are converted through
well-known AID devices 18 in a data
conversion module 20 to generate digital data corresponding to the analog
signals 16. This data is made available on a
data bus 22.
A processing module 24 processes data on the bus 22 to generate usable
quantitative measures of patient
activity as well as to compare and create object displays that, for example,
(1) relate certain data relative to other data;
(2) present data in context; (3) relate data to a frame of reference; (4)
determine the rate of change information in the
data; andlor (5) to present event information.
One embodiment of the module 24 thus includes a plurality of data processing
sections 26 that analyze andlor
quantify the data being input from the probe 12. For example, one section 26a,
connected in the data chain to probe 12a,
processes data on the bus 22 to provide a representation of heart rate in the
form of a digital word. As the patient's heart
rate changes, so does the digital word. A memory module 28 is used to store
selected data, such as the digital word
corresponding to heart rate, so that the module 24 contains a record and a
current value of the patient's heart rate
activity. The memory 28 also stores information, such as nominal values from
which to compare data to a frame of
reference, or such as extreme values representative of desired patient
thresholds. The display driver section 30, connected
to the sections 26, can thus command the display of the heart rate data in
context on the display 32, andlor relative to
frame of reference data within the memory 28.
The data from the sections 26 can also be compared to other data or related to
stored thresholds within the
assessment module 34. By way of example, data corresponding to probe 12a can
be compared relative to probe 12b
through a process of digital division within the module 34. The driver 30 can
in turn command the display of this related
data on the display 32. In another example, the assessment module 34 can
compare other data to stored data within the
memory 28; and a warning event can be displayed on the display 32 if the
comparison exceed a set threshold.
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WO 99/39633 PCT/US99/02798
Those skilled in the pertinent technology should appreciate that certain
probes 12 may have self-contained A!D
conversion capability and data manipulation. Furthermore, such probes can
easily be connected directly to the assessment
module 34 and memory 28 by known techniques.
The system 10 is controlled by inputs at a user interface 36, such as a
keyboard, and the display driver 30
formats data into various object formats 40 on the display 32. Accordingly, by
commanding selected processes within the
assessment module 34 - such as comparison of certain data with other data -
such data can be automatically displayed on
the display 32 in the desired object format. The particular object formats,
according to the invention, are described below.
Preferably, these objects are displayed simultaneously on the same display so
as to provide a comprehensive data profile
to the operator.
Figure 2 shows a representative computer system 155 that may be used in
conjunction with the system 10 of Figure
1. System 155 can be operated in a stand-alone configuration or as part of a
network of computer systems. The system 155
is an integrated system that collects data from the patient and presents
processed data to a display for viewing by a physician.
The computer system 155 includes blood-monitoring software executed in
conjunction with an operating system, for
instance Windows 95 available from Microsoft Corporation, on a computer 160.
Other embodiments may use a different
operational environment or a different computer or both.
In an alternate embodiment of the invention, the computer 160 can be connected
via a wide area network (WAN)
connection to other physicians or hospitals. A WAN connection to other medical
institutions enables a real-time review of the
patient's progress during surgery or in the intensive care un'tt.
Referring again to Figure 2, one embo~ment of the computer 160 includes an
Intel Pentium or similar microprocessor
running at 300 MHz and 32 Megabytes (Mb) of RAM memory (not shown?. The system
155 includes a storage device 165,
such as a hard disk drive connected to the processor 170. The hard drive 165
is optional in a network configuration, i.e., the
workstation uses a hard disk or other storage device in a file server. If the
computer 160 is used in the stand-alone
configuration, the hard drive 165 is preferably 100 Mb or more. However, the
system is not limited to particular types of
computer equipment. Any computer equipment that can run the display system
described herein is anticipated to function
within the scope of this invention.
The computer 160 is integrated with a group of computer peripherals, and is
connected to a UGA (video graphics
array display standard, or better, color video monitor, which provides the
display output of the system 155. The display 175
may be a 17 inch monitor running at 1024 x 768 pixels with 65,536 colors. A
keyboard 180 that is compatible with IBM AT
type computers may be connected to the computer 160. A pointing device 185,
such as a two or three button mouse can also
connect to the computer 160. Reference to use of the mouse is not meant to
preclude use of another type of pointing device.
A printer 190 may be connected to provide a way to produce hard-copy output,
such as printouts for file records. In
one configuration, a backup device 195, such as a Jumbo 250Mb cartridge tape
back-up unit, available from Colorado Memory
Systems, is preferably connected to the computer 160.
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WO 99/39633 PCTNS99/02798
In an alternate embodiment of a stand-alone configuration, or as one of the
workstations of a network configuration,
the system 155 may include a portable computer, such as a laptop or notebook
computer, e.g., a Premium Executive 386SXl20,
available from AST Research, or other computers available from a variety of
vendors. The portable computer Inot shown) is
equipped with components simgar to that described in conjunction with computer
160.
It will be understood by one skilled in the technology that a programmed
computer can also be implemented
completely or partially with custom circuitry. Therefore, the chosen
implementation should not be considered restrictive in any
matter.
II. Software
Many different ways of implementing the software of the present invention will
be known to skilled technologists.
For example, programming languages such as Labview, C++, Basic, Gobol, Fortran
or Modula-2 can be used to integrate the
features of the present invention into one software package. An alternative
method of illustrating the software of the present
invention is to use a spreadsheet program to collect and determine the PvOz of
a patient in real-time. This method is described
in detail below.
A. Determining Blood Gas Levels
As discussed above, the systems and methods of the present invention collect
data from a patient and determine
various tissue oxygenation parameters of a patient in real-time. Software is
used to direct this process. Those skilled in the art
will appreciate that the desired parameters may be derived and displayed using
various software structures written in any one
of a number of languages. Figure 3 illustrates one possble software scheme
that could be used in conjunction with the
disclosed methods and systems.
Referring now to Figure 3, the process is begun when a start signal is
transmitted by the user to the system at start
state 200. The start signal can be a keystroke of mouse corrxnand that
initiates the software to begin collecting data. After
receiving the start command at state 200, arterial pressure data is collected
from a patient at state 202. Arterial pressure data
may be collected by hooking a patient up to an arterial pressure monitor as is
well known.
Once data have been collected from a patient at state 202, a "data in range"
decision is made at decision state 204.
At this stage, the software compares the data co~ected at state 202 with known
appropriate ranges for arterial pressure
values. Appropriate ranges for arterial pressure data are, for example,
between 70!40 and 2501140.
If data collected at process state 200 are not within the range programmed in
decision state 204, or if the arterial
pressure wave is abnormal an errorlexception handling routine is begun at
state 206. The error handling routine at state 206
loops the software back to process state 202 to re-collect the arterial
pressure data. In this manner, false arterial pressure
data readings will not be passed to the rest of the program. If the data
collected at process state 202 are in the appropriate
range at decision state 204, the software pointer moves to process state 208
that contains instructions for collecting arterial
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WO 99/39633 PCT/US99/02798
data. Preferably the collected data will include patient temperature, arterial
pH, h~noglobin levels, PaOz and PaCOZ. Moreover,
the data is preferably generated by an attached blood chemistry monitor which
may provide information on the patient's blood
gas levels, acid-base status and hematology status. In such embodiments the
data is collected by receiving data streams via
the serial connection from the blood chemistry monitor into the computer.
Alternatively, the relevant values may be obtained
from accessing data that is manually input from the keyboard.
As described previously, the blood chemistry monitor continually samples
arterial blood from the patient preferably
determining several properties of the patient's blood from each sample. Data
corresponding to each of the properties taken
from the blood chemistry monitor at process state 208 are checked so that they
are in range at decision state 210. An
appropriate range for the pH is 7.15 to 7.65. An appropriate range for the
hemoglobin level is from 0 to 16 gldL. An
appropriate range for the Pa02 is from 50 mm Hg to 650 mm Hg while an
appropriate range for the PCOZ is from 15 mm Hg to
75 mm Hg.
If data are not within the appropriate ranges for each specific variable at
decision state 210, an errorlexception
handling routine at state 212 is begun. The errorlexception handling routine
at state 212 independently analyzes variables
collected at state 208 to determine whether it is in range. If selected
variables collected at state 208 are not within the
appropriate range, the errorlexception handling routine 212 loops a software
pointer back to state 208 so that accurate data
can be collected. If the selected data are in range at decision box 210, the
software then derives the CaOz value along with the
cardiac output (C0) from the previously obtained arterial pressure data at
state 214.
As discussed, cardiac output can be derived from arterial pressure
measurements by any number of methods. For
example, the Modelflow system from TNO Biomedical can derive a cardiac output
value in real-time hom an arterial pressure
signal. Other methods, as discussed above, could also be used at process step
214 to determine cardiac output. Once a
cardiac output value has been determined at process step 214, the patient's
total oxygen transport ~DOZ) may be derived at
process step 215. As previously discussed the total oxygen transport is the
product of the cardiac output and the arterial blood
oxygen content. This parameter may optionally be displayed and, as indicated
by decision state 217, the program terminated if
the software has received a stop command. However, if the software has not
received a keyboard or mouse input to stop
collecting data at decision state 217, a pointer directs the program to
process state 216 to derive further parameters.
Specifically, process state 216 relates to the measurement or input of the
patient's V02.
The patient's VOz can be calculated using the methods previously described
measured by hooking the patient up to a
suitable ventilator and measuring his oxygen uptake through a system such as
the Physioflex discussed above or using a number
of other devices such as systems manufactured by Sensormedics and Puritan
Bennett. By determining the amount of oxygen
inspired and expired, the ventilator may be used to calculate the total amount
of oxygen absorbed by the patient. After the
patient's VOZ value has been determined at process step 216, these variables
are applied to the Fick equation at state 218 to
provide a real time CvOz. The Fick equation is provided above.
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Once the CvOz is known, mixed venous oxyhemoglobin saturation (SvOz) and the
mixed venous oxygen tension (Pv02)
can be derived at state 220. As previously explained, values for mixed venous
pH and PCOz are assumed to have a constant
(but alterable) relation to arterial pH and PaCOz respectively and these are
used, along with other variables, in the Kelman
equations to define the pos-rtion of the oxyhemoglobin dissociation curve.
Alternatively, algorithms can be derived to calculate
these values. Knowing the Hb concentration, a PvOz is derived that then
provides a total CvOz (which includes contributions
from Hb, plasma and PFC) equal to the CvOz determined from the Fick equation.
If the CvOz value will not "fit" the Fick
equation, another PvOz value is chosen. This process is repeated until the
Fick equation balances and the true Pv02 is known.
Those skilled in the art will appreciate that the same equations and
algorithms may be used to derive, and optionally
display, the mixed venous blood oxyhemoglobin saturation SvOZ. That is, Sv02
is closely related to Pv02 and may easily be
derived from the oxygen-hemoglobin dissociation curve using conventional
techniques. It will further be appreciated that, as
with Pv02, SvOz may be used to monitor the patient's oxygenation state and as
an intervention trigger if so desired by the
clinician. As discussed above, mixed venous blood oxyhemoglobin saturation may
be used alone in this capacity or,.more
preferably, in concert with the other derived parameters.
After deriving values for Pv02, SvOz or both, the value or values may be
displayed on the computer display at step
222. If the software has not received a keyboard or mouse input to stop
collecting data at decision state 224, a pointer loops
the program back to process state 202 to begin collecting arterial pressure
data again. In this manner, a real-time data loop
continues so that the patient's mixed venous blood oxygen tension (Pv02) or
saturation (Sv02) is constantly updated and
displayed on the computer at state 222. If the software has received a stop
command from a keyboard or mouse input at
decision state 224, then a finish routine 226 is begun.
B. Calculstisg Oxygen Tisasport values
The following system utilizes a large Microsoft EXCEL° spreadsheet to
collect information from the patient and
display the desired parameters including PvOz, Sv02 and 002. Before receiving
real-time inputs of cardiovascular and
oxygenation variables, a number of oxygenation constants may be entered into
the system. These constants preferably include
the patient's estimated blood volume, oxygen solubility in plasma and the
oxygen content of 1 g of saturated oxyhemoglobin.
The oxygenation constants are then stored in the computer's memory for use in
later calculations.
TABLE 1 shows commands from part of a Microsoft EXCEL° spreadsheet that
collects a patient's data and derives
the value of the desired oxygenation parameters. The program is initialized by
assigning names to various oxygenation
constants that are to be used throughout the software. In the embodiment
shown, oxygenation constants corresponding to
blood volume (BVI, oxygen solubility in a perfiuorocarbon emulsion (02SO1),
specific gravity of any perfluorocarbon emulsion
(SGPFOB), intravascular half-life of a perfluorocarbon emulsion (HL),
weightlvolume of a perfluorocarbon emulsion (CONCI,
barometric pressure at sea level (BARD), milliliters oxygen per gram of
saturated hemoglobin (Hb0) and milliliters of oxygen per
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WO 99/39633 PCT/US99/02798
t OOmI plasma per 100mm of mercury (PI0) are all entered. The constants
relating to perfluorocarbons would be entered in the
event that fluorocarbon blood substitutes were going to be administered to the
patient.
An example of starting values for Kelman constants, a s~set of the oxygenation
constants, is also shown in TABLE
1. These starting values are used in later calculat'rons to derive the
patient's mixed venous oxygenation state or other desired
parameters such as mixed venous blood oxyhemoglobin saturation. As with the
other oxygenation constants the Kehnan
constants are also assigned names as shown in TABLE 1.
TABLE 1
ASSUMPTIONS: VALUES
AT
START:
Blood Volume (mllkg) -BV 70
02 solubility in PFB (mlldl 52.7
X37 deg C) -02SOL
Specific Gravity of PFOB -SGPFOB 1.92
Intravascular half-life of - 112 Life
Oxygent HT (hours) -HL of Oxygent
WgtIVol of PFOB emulsionl100 0.6
-CONC
Barometric Pressure @ sea level 760
-BARO
MI 02 per gram saturated Hb 1.34
-Hb0
MI 02 per 100 ml plasma per 0.3
100 mm Hg -HIO
KELMAN CONSTANTS: VALUES
AT START
Ka 1 --8.5322289"
1000
Ka2 -2.121401"1000
Ka3 --6.7073989"
10
Ka4 -9.3596087"
100000
Ka5 --3.1346258"
10000
Ka6 -2.3961674"
1000
Ka7 -67.104406
After the oxygenation constants, including the Kelman constants, have been
assigned names, real time inputs from
the arterial pressure lines and blood chemistry monitor may be initialized and
begin providing data. As shown in TABLE 2, the
system depicted in this embodiment derives or receives data relating to the
arterial oxyhemoglobin saturation percentage (Sa0zl.
In particular, saturation percentages are derived from arterial data for
oxygen tension fPa02), pH (pHa), carbon dioxide tension
(PaC02) and body temperature (TEMP). If desired by the clinician, the present
invention provides for the real.time display of
SvOz values (as derived from calculated PvOz, pHv, PvCOZ and temperature) to
be used for the monitoring of the patient's tissue
oxygenation status. As previously discussed, values for PvC02 and pHv are
related, by a fixed amount, to those of PaC02 and
pHa respectively as determined by algorithms. Cardiac output (C0) is also
input as is VOz. Figure 4 provides a schematic
representation of this procedure and resuhing data.
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WO 99/39633 PCTNS99/02798
When Hb concentration, arterial blood gas and acidlbase parameters are entered
(automatically or manually) into the
program, the 02 delivery and consumption variables for both red cell
containing Hb and for the plasma phase may be determined.
Those variables relating to PFC (in the case of blood substitutes) or Hb based
oxygen carrier can also be determined.
Referring again to Figure 4, numerical values useful for the calculation of
CaOz relate to Hb concentration, arterial
oxygen tension 1Pa02), arterial carbon dioxide tension (PaCO~), arterial pH
(pHa) and body temperature. The position of the
oxygen-hemoglobin dissociation curve is calculated using the Kelman equations,
which are input as oxygenation constants in the
program. These calculations produce a curve that, over the physiological range
of OZ tensions, is indistinguishable from the
parent curve proposed by Severinghaus IJ. Aoul. Physiol. 1966, 21: 1108-11161
incorporated herein by reference. As shown
schematically in Figure 4, iteration may be used to calculate a Pv02 (via
Sv02) that results in the required mixed venous oxygen
I O contents in Hb, plasma and fluorocarbon to satisfy the Fick equation.
-1.8-
CA 02321227 2000-08-24
WO 99/39633 PCT/US99/02798
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- 19 -
CA 02321227 2000-08-24
WO 99/39633 PCTNS99/02798
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- 20 -
CA 02321227 2000-08-24
WO 99/39633 PCTNS99/02798
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- 21 -
CA 02321227 2000-08-24
WO 99/39633 PCT/US99/02798
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- 22 -
CA 02321227 2000-08-24
WO 99/39633 PCTNS99/02798
Based on the numeric values provided, the program calculates oxygenation
parameters such as Pv02 and SvOZ in
real tune, as shown in TABLE 2. These values are then fed into the display
system described below to generate perceptual
diagrams. These ~agrams are then used by the physician to determine, for
example, when to give the patient a blood
transfusion or alter the patient's clinical management. Significantly, the
displayed values may be used to monitor the
S physiological effects of blood substitutes, including those based on
hemoglobin or perfluorochemicals following their
administration.
TABLE 3 and TABLE 4 show additional information that may be provided by the
instant invention further
demonstrating its utility and adaptability. More specifically, TABLE 3
provides various oxygenation values that may be
calculated using the methods disclosed herein while TABLE 4 provides other
indices of oxygen consumption and oxygen delivery
that are useful in optimizing patient treatment.
A closer examination of TABLE 3 shows that the system of the present invention
may be used to provide the
individual oxygen content of different constituents in a mixed oxygen carrying
system. In particular, TABIE 3 provides
calculations that give the arterial or venous oxygen content of circulating
hemoglobin, plasma and fluorochemical respectively.
Such values would be of particular use when intravenously introducing
fluorochemical emulsion blood substitutes in conjunction
with surgical procedures.
TABLE 4 illustrates that the present invention may also be used to provide
real-time information regarding oxygen
consumption and delivery. As mentioned previously, Hb or Hct measurements are
not a suitable reflection of tissue
oxygenation. This is mainly because they only give an indication of the
potential arterial OZ content (Ca02), without provirung
information about the total oxygen transport (DOz) to the tissues where it is
to be used. However as seen in TABLE 4 the
instant invention solves this problem by providing on line oxygen transport
information which is derived based on CaOz and
cardiac output (CO).
Currently cardiac output is measured using thermodilution, and Ca02 is
calculated typically by measuring the arterial
oxyhemoglobin saturation (SaOZ) and hemoglobin levels, and inserting these
values into the following equation: Ca02 - ([Hb] X
1.34 X Sa02) + (PaOZ X 0.003], where [Hb] - hemoglobin concentration (in
gldL); 1.34 - the amount of oxygen carried per
gram of fully saturated hemoglobin; PaOZ - the arterial oxygen tension; and
0.003 is the amount of oxygen carried by the
plasma (per deciliter per mm Hg of oxygen tension].
The present invention combines the continuous cardiac output algorithm with
the Kelman equations to provide the
position of the oxygen hemoglobin association curve. Using on-line and off-
line inputs of body temperature, hemoglobin, and
arterial blood gases, the present invention is able to trend DOZ on a
continuous basis. The factors used to determine D0~ are
displayed along with their product; thus, the etiology of a decrease in DOZ
(inadequate cardiac output, anemia, or hypoxia)
would be readily apparent to the physician, decisions regarding the
appropriate interventions could be made expeditiously, and
the results of treatment would be evident and easily followed.
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WO 99/39633 PCT/US99/02798
More particularly, preferred embodiments of the invention may be used to
provide and display real-time D02, arterial
blood gases, hemoglobin concentration and CO (and ag other hemodynamic data
already discussed such as BP, heart rate,
systemic vascular resistance, rate pressure product and cardiac work). As
shown in TABLE 3, such embodiments can also
provide separate readouts of contributions of Hb, plasma and PFC (if in
circulation) to DOZ: That is, the oxygen contributions of
each component may be accurately monitored and adjusted throughout any
therapeutic regimen. Such data would be
particularly useful in both the OR and ICU for providing a safety cushion with
respect to the oxygenation of the patient.
The importance of maximizing DOZ for certain patients in the ICU has been
underscored by recent studies. The
present invention may also be used for determining when such intervention is
indicated and to provide the data necessary for
achieving the desired results. Once DOZ is known it is possible to calculate
the maximum OZ consumption (VOZ) that could be
supported for a certain chosen land aherable) PvOz. As previously discussed,
this value may be termed deliverable oxygen
(dDOz). For instance, a PvOZ of 36 mm Hg might be chosen for a healthy 25 year
old patient, where as a PvOz of 42 mm Hg or
higher might be needed for an older patient with widespread arteriosclerosis
or evidence of coronary atheroma or myocardial
ischemia. Oxygen consumption under anesthesia is variable, but almost always
lies in the range of 1.5 to 2.5 mllkglmin. If the
supportable Y02, at the chosen PvOz, was well above this range all would be
well and no intervention would be necessary. The
closer the supportable Y0z to the normal Y02 range the earlier intervention
could be considered.
This relationship could be used to provide a single value, based on
deliverable oxygen (dDDz) vs. oxygen consumption
(Y02), that would simplify patient care. As previously explained, dD02 is the
amount of oxygen transported to the tissue that is
able to be delivered before the partial v~ous oxygen pressure (PvOz) and, by
implication, tissue oxygenation tension falls below
a defined level. Thus, if it is desired that the PvOz value not fall below 40
(this number is variable for different patients
depending on their general medical cond'ttion) then DOZ land by implication
dD02) must be maintained at sufficient levels.
The supplyldemand ratio (dDOzNOZ) for a selected PvOZ can be used to provide a
single value showing that the
amount of oxygen being administered is sufficient to maintain the desired
oxygenation state. For example, if it is known that
the dDOz required to maintain a PvOz of 40 is, say, 300 mllmin and the
measured (Y0z) is 200 mllmin then the patient is being
supplied with enough oxygen for his needs. That is, the supplyldemand ratio is
300 mllmin 200 mllmin or 1.5. A
supplyldemand ratio of 1 would imply that the Pv02 (or other selected
parameter i.e. SvOz) was at the selected trigger value
(here 40 mm Hgl. Conversely, if the dD02 (deliverable oxygen) is 200 mllmin
and the VOZ (oxygen consumption) is 300 mllmin
then the ratio is 0.66 and the patient is not receiving sufficient oxygen
(i.e., the Pv02 wig be less than 40). Continuous
monitoring and display of this ratio will allow the clinician to observe the
value approaching unity and intervene appropriately.
III. Displaying Objects Related to Physiological Values
As discussed above, the computer system 155 of Figure 2 includes software and
systems for displaying medical
process diagrams relating the values calculated above.
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The display system collects the oxygen transport values and creates display
objects that are presented to the
physician. Although some of the data may be derived by reading raw analog or
digital data from a patient monitor, many
of the values may be read from calculated data such as shown in TABLES 1-4
above.
The system might sample the data at 200 times per second, and update the
display every 2 seconds. However,
the system may be capable of higher sampling and display updates to provide
the most up to date data to the physician.
As discussed above, the perceptual diagrams comprise a series of data objects
representing physiological
processes in the body. Examples of these data objects include a red blood cell
object, a heart pump object, a vascular
resistor object, an alveolar-arterial object, an acid-base object and a
metabolism object. These objects, as discussed
below, can be displayed alone or together to provide a perceptual diagram of
an oxygen transport system in a patient.
A. The Bed Blood CeII Object
This graphical display object contains information regarding the quantity of
red cells (as the hemoglobin), the
oxygen loading of the red cells (as the percent oxygen saturation) and the
oxygen content (using an accepted formula).
The size of a circle correlates with the hemoglobin. The portion of the circle
filled black from the bottom up, correlates
1 S with the oxygen saturation. The product of the hemoglobin and the oxygen
saturation correlates with the oxygen content
(Ca02) pointer on the left.
More specifically, referring to Figure 5, a red blood cell object 300 displays
information relating to the amount of
hemoglobin in a patient's blood, the amount of oxygen which is loaded onto the
red blood cells, the effect of temperature
on blood viscosity, and the oxygen content of the blood. In one aspect, this
relationship can be formulated by the
following equation: Arterial Oxygen Content - (Arterial Oxygen Saturation/ x (
Hemoglobin) x 11.34). In Figure 5, Arterial
Oxygen Saturation is labeled "Sa02", hemoglobin is labeled as "HB", and
Arterial Oxygen Content is labeled as "CaOz".
These red-blood cell related values are then converted to a perceptual diagram
(e.g., on a computer display 32,
Figure 1) in the form of a pair of nonconcentric circle sets 310a, 310b. As
indicated in Figure 5, there is an arterial portion
314 and venous portion 316 of the red blood cell object 300. In the arterial
portion 314, the patient's Ca02 value is
indicated by a diamond 320 and is mapped to the Y-axis. The patient's
hemoglobin level, the volume percentage of
erythrocytes in whole blood, is mapped to the X-axis. In the venous portion
316, the patient's CvOZ is indicated by a
diamond 330 and is mapped to the Y-axis- The hemoglobin level is mapped to the
X-axis.
The nonconcentric circles 310a,b are created by using a Y-axis to define a
tangential line along the left-most
point 340a,b of the nonconcentric circles 310a,b. Each nonconcentric circle
includes the same left-most point 340a,b
along the Y-axis.
As the level of arterial oxygen increases, the CaOZ diamond 320 moves upward
along the Y-axis. A horizontal
oxygen extraction line 350 indicates the level of arterial oxygenation by
defining the upper boundary of a shaded area 360
in the arterial red-cell shaped object 310a. The red cell objects 310a,b can
be partially or completely shaded, as illustrated
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WO 99/39633 PCT/US99/02798
in Figure 5 to show the percent filled with oxygen of the patient's red blood
cells (e.g., when half shaded, the cell is only
half filled with oxygen). As the level of hemoglobin (Hb) in the patient
increases, the shading is with respect to tan
increased circumference circle of the red-cell shaped object 310a,b also
increases.
Similarly for the venous red cell shaped object 310b, as the level venous
oxygenation rises and falls in the
patient, the CvOz diamond 330 moves up and down along its Y-axis. As the CvOz
diamond 330 moves up and down, the
amount of shading 370 within the venous red-cell shaped object 310b changes.
Thus, the oxygenation on the venous side
of the vascular circuit is readily illustrated to the physician. When the
arterial and venous oxygen contents are compared
by looking at the relative shading 360 /arterial side) and 362 (venous sideh a
rapid, perceptual understanding of oxygen
extraction is made evident. As is known, Oxygen Extraction - (Arterial Oxygen
Content) - (Venous Oxygen Content). Thus
by comparing the relative shading of the red-cell shaped objects 310a and
310b, a physician can perceptually understand
the amount of oxygenation extraction in the patient.
The oxygen extraction line 350 is extended from the arterial blood cell 310a
to an oxygen extraction sliding scale
364. In turn, the oxygen extraction sliding scale 364 maintains the Cv02
diamond 330 as its lower boundary. As the level
of CaOZ rises, the oxygen extraction sliding scale 364 increases. Similarly,
as the level of CvO~ drops, the oxygen
extraction sliding scale 364 also increases. This makes sense since the amount
of oxygen extraction is expected to
increase with rising arterial oxygen pressure or with decreasing venous oxygen
pressure. A physician can thereby look to
the oxygen extraction sliding scale 364 as a quick measure of the amount of
oxygen extraction taking place in the patient.
The manner in which the red-cell object 300 mimics the in vivo action of
actual red blood cells makes the red-cell object
300 very intuitive to a physician.
Referring now to Figure 6, a process 370 of updating the red cell object 300
begins at a start state 372. The
process 370 then moves to a state 374 wherein the Ca02 value for the patient
is read. As discussed above, this value can
be read from a data table or from any type of memory storage in the computer
system. Once the Ca02 level is read at the
state 374, the process 370 moves to a decision state 376 to determine if the
Ca02 value has changed from the fast
sampling. If the Ca02 value has changed, the process 370 moves to a decision
state 378 to determine whether the CaOz
value has increased or decreased. If the CaOz value has increased, the Ca02
indicator 320 and oxygen extraction line 350
are moved up vertically along the Y-axis at a state 382. However, if the Ca02
has decreased, the process 370 moves to a
state 380 wherein the CaOz indicator 320 and oxygen extraction line 350 are
moved downward along the Y-axis. The
process 370 then moves to a state 384 wherein the CvOZ value is read.
A determination is then made at a decision state 386 whether the CvOz value
has changed since the last data
sampling. If the value has changed, the process 370 moves to a decision state
387 to determine whether the Cv02 value
has increased or decreased. If a determination is made that the Gv02 value has
increased, the process 370 moves to a
state 390 wherein the CvOZ indicator 330 is moved upwards along its Y-axis.
Similarly, if a determination is made at the
decision state 387 that the Cv02 value has decreased, the process 370 moves to
a state 389 wherein the Cv02 indicator
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WO 99/39633 PCT/US99/02798
330 is moved downward along 'tts Y-axis. The process 370 then moves to a state
391 wherein the hemoglobin value of
the patient is read.
The process 370 then moves to a decision state 392 to determine whether the
hemoglobin value has changed
since the last sampling. If a determination is made that the hemoglobin level
has changed, the process 370 moves to a
decision state 394 wherein a determination is made whether the hemoglobin
value has increased or decreased. If the
hemoglobin level has increased, the process 370 moves to a state 397 wherein
the shaded area 360 is increased in size to
indicate a larger quantity of red blood cells in the patient's blood. However,
if a determination is made at the decision
state 394 that the hemoglobin level has decreased, the process 370 moves to a
state 395 wherein the shaded areas, 360-
362 are reduced in circumference. The process 370 then terminates at an end
state 399.
B. The Neart Pump Object
This graphical display object contains information regarding blood flow (as
cardiac output), pulse rate (as derived
from an arterial transducer) and stroke volume (using an accepted formula).
The resulting rectangle (defined by the pulse
rate and the stroke volume) is filled black during the diastolic phase of the
cardiac cycle. During the systolic phase of the
cardiac cycle, the rectangle empties from the top down at a rate defined by
correlates of cardiac contractility (such as
dPldtl.
Referring specifically to Figure 7, a heart pump object 400 displays the
following relationship: Cardiac Output -
(Stroke Volume) x (Heart Rate). In one aspect, the heart pump object 400 is
displayed as a rectangle 410 wherein the area
of the rectangle 410 represents the cardiac output of the patient. The amount
of blood pumped with each stroke, the
stroke volume (SV), of the heart is thus represented by a diamond 420 on the X-
axis. The heart rata (HR) is represented as
a diamond 430 along the X-axis. With each heart beat, the heart rate and
stroke volume are calculated and plotted to this
diagram. The rectangle 410 is divided into a right ventricular (RV) metaphor
440 and left ventricular (LV) metaphor 450 by
dividing the size of the rectangle 410 in half along the X-axis. The shape of
a low Stroke Volume ventricle would be
reflected by a rectangle 410 that is short and wide, while the shape of a
bradycardic ventricle with a normal SV would be
indicated by a rectangle 410 that is tall and thin.
The filling pressure or volume information, or contractility of the heart
chambers (right and lefty is presented in
the form of a central venous pressure (CVP) analog gauge 452 and Pulmonary
Artery Capillary Wedge Pressure (WP)
analog gauge 454 located on the X-axis. For both analog meters 452, 454, the
12 o'clock position is defined as normal.
Thus, when the CVP and WP are read as normal, the rectangle 410 has squared
sides.
However, because the CVP analog meter 452 scribes an arc along the X-axis, if
a CVP reading is not normal, the
left side 456 of the rectangle 410 will bow in or out. When the left side 456
bows outward due to a high CVP, it
represents a distended, overfilled left ventricle. Similarly, when the left
side 456 bows inward due to a low CVP, it
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WO 99/39633 PCT/US99/02798
indicates an empty, under-filled left ventricle. As can be imagined, the
bulging shape of the left side 456 of the rectangle
410 readily conjures up images of the in vivo heart being over-filled with
blood.
When the WP is not normal, the WP analog meter 454 scribes an arc along a
right side 480 of the rectangle 410.
As the WP increases, the right side 458 bulges outward indicating a swollen,
overfilled right ventricle in the patient. In
addition, as the WP decreases, the WP analog meter 454 scribes a scalloped arc
along the right side 458 so that the right
ventricle is illustrated as an empty, unfilled ventricle. The right side 458
and left side 456 correspond with the image of
the heart seen with a long-axis four chamber view using transesophageal echo-
cardiography. Thus, it is readily apparent
to an anesthesiologist when the right or left ventricles are either under-
filled or overfilled during surgery by noting not only
the relative dimensions of the rectangle 410, but also the shapes of its
sides.
Referring now to Figure 8, the process 460 of modulating the heart pump object
400 is described. The process
460 begins at a start state 462, and then moves to a state 463 where the
stroke volume (SU1 is read. As can be
imagined, stroke volume can be read from a table or buffer in the computer
system. The process 460 then moves to a
decision state 465 to determine whether the stroke volume has changed since
the last reading. If the stroke volume has
changed, the process 460 moves to a decision state 466 to determine whether
the stroke volume has increased or
decreased.
If the stroke volume has decreased, the process 460 moves to a state 468
wherein the stroke volume indicator
420 is moved downward along the Y-axis. As illustrated in Figure 7, as the
stroke volume indicator 420 is moved
downward along the Y-axis, the shaded rectangle 410 is reduced in height. If a
determination is made at the decision state
466 that the stroke volume has increased, the process 460 moves to a state 469
wherein the stroke volume indicator 420
is moved upward along the Y-axis. This, in turn, increases the height of the
shaded rectangle 410. The process 460 then
moves to a state 470 wherein the patient's heart rate is read. A determination
is then made at a decision state 471
whether the heart rate has changed from the last reading.
If the heart rate has changed since the last reading, a determination is made
at a decision state 473 whether the
heart rate has increased or decreased. If the heart rate has decreased, the
process 460 moves to a state 474 wherein the
heart rate indicator is moved to the left along the X-axis of the heart pump
object 400. However, if a determination is
made at the decision state 473 that the heart rate has increased, the process
460 moves to a state 475 wherein the heart
rate indicator 430 is moved to the right along the X-axis of the heart pump
object 400. As can be imagined upon review of
Figure 7, as the heart rate indicator 430 is moved horizontally along the X-
axis, the width of the shaded rectangle 410 is
increased and decreased accordingly.
The process 460 then moves to a state 477 wherein the central venous pressure
(CUP) value is read. A
determination is then made at a decision state 478 whether the CVP has changed
since the last reading. If the CUP has
changed, a determination is made at a decision state 479 whether the CUP has
increased or decreased. If the CUP has
decreased, the process 460 moves to a state 480 wherein the analog CUP gauge
452 is moved to the right along its
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WO 99/39633 PCTNS99/02798
predetermined arc. As discussed above, as the CVP analog gauge 452 is moved to
the right along its arc, the shape of the
right ventricular metaphor 440 is altered to indicate a less filled heart
chamber.
If a determination was made at the decision state 479 that the CVP has
increased, the process 460 moves to a
state 482 wherein the CUP analog gauge 452 is moved to the left along its arc,
the left side 456 of the right ventricular
metaphor 440 begins bulging outward to indicate a swollen heart chamber. The
process 460 then moves to a state 483
wherein the wedge pressure (WP) value is read.
The process 460 then moves to a decision state 485 to determine whether the
wedge pressure has changed
since the last reading. If the wedge pressure has changed, a determination is
made at a decision state 486 whether the
value of the wedge pressure has increased or decreased. If the value of the
wedge pressure has decreased, the process
460 moves to a state 488 wherein the wedge pressure analog gauge 454 is moved
to the left along its predetermined arc.
As the analog gauge 454 is moved to the left, the side 458 of the left
ventricular metaphor 450 becomes more concave
indicating a less-filled heart chamber. In addition, as the value of the
patient's heart rate (HR) changes, the WP analog
gauge is slide left to right along the X-axis. As the heart rate increases,
the WP analog gauge slides right, while as the HR
decreases, the WP analog gauge slides left.
1 S However, if a determination is made at the decision state 486 that the
wedge pressure has increased, the
process 460 moves to a state 490 wherein the wedge pressure gauge 454 is moved
to the right along its predetermined
arc. As can be envisioned upon review of the heart pump object 400, as the
wedge pressure analog gauge 454 is moved
to the right, the edge 458 of the left ventricular metaphor 450 is curved
outward indicating a bulging or swollen heart
chamber. The process 460 then ends at an end state 492.
C. The Vascular IPesistor Object
This graphical display object contains information regarding Ohm's Law of
Fluid Flow. The perfusion pressure is
shown on the left pressure scale and is defined by the mean arterial pressure
(MAP1 and the central venous pressure (CVP).
The blood flow is shown on the right pressure scale and is defined by the
cardiac output pointer (CO). The perfusion
pressure and cardiac output are centered and connected to each other using a
meter showing the systemic vascular
resistance (SVR) such that a tube is formed which appears "dilated" when the
SVR is low and appears "constricted" when
the SVR is high.
Turning to Figure 9, a vascular resistor object 500 is used to display the
blood flow equivalent of Ohm's Law.
This display is used by medical personnel to optimize the hemodynamic
physiology of patients during surgery. The vascular
resistor object 500 represents the following equation: (Mean Arterial
Pressure) - (Central Venous Pressure) - (Cardiac
Output) x iSystemic Vascular Resistance). The data is displayed in the object
500 such that the shape of a "pipe" emerges
w'tth flow from left to right. Two lineal scales relating to the pressure
gradient for blood flow and the actual cardiac
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CA 02321227 2000-08-24
WO 99/39633 PCT/US99/02798
output in liters per minute are shown as a function of the systemic vascular
resistance (SVR) such that a "pipe" metaphor
emerges.
A set of two Y-axes are used to produce the vascular resistor object 500. A
left Y-axis includes a mean arterial
pressure IMAPI indicator 510 and a central venous pressure (CUP) indicator
515. A blood input area 520 between the
MAP indicator 510 and CVP indicator 515 indicates "inflow" of blood into the
pipe. In contrast, a blood output area 521
indicates the "outflow" of blood from the pipe. A right Y-axis includes a
cardiac output (C0) indicator 524 that reflects the
calculated cardiac output of the patient. This is the outflow portion of the
pipe. An SUR analog gauge 528 is disposed on
the X-axis linking the right and left Y-axes. If the normal SUR is set at the
3 o'clock position on the SVR analog gauge
528, a low reading gauge downward causing the pipe to open. In contrast, a
high SUR reading causes the gauge to move
upward indicating a more closed pipe as shown in Figure 9.
To translate into physiological terms, as the SUP increases, the flow of blood
is reduced, as indicated by a
constricted pipe. As the SUP decreases, the flow of blood is increased, as
indicated by a more open pipe. The MAP
indicator 510 can also affect the model, since an increasing MAP widens the
inflow so more overall blood flow is found.
As can be imagined, the vascular resistor object 500 closely reflects the
actual physiology of the patient. It is thus an
intuitive object for deciphering complex situations in a patient.
Referring to Figure 10, a process 535 of updating the vascular resistor object
500 is described. The process 535
begins at a start state 537 and then moves to a state 539 wherein the mean
arterial pressure (MAP) is read. A
determination is then made at a decision state 541 whether the MAP has changed
since the last reading. If the MAP has
changed, the process 535 moves to a decision state 542 to determine whether
the MAP has increased or decreased. If
the MAP has decreased, the process 535 moves to a state 544 wherein the MAP
indicator 510 is moved downward along
the Y-axis of the vascular resistor object 500. However, if a determination is
made at the decision state 542 that the
MAP has increased, the process 535 moves to a state 546 wherein the MAP
indicator 510 is moved upwards along the X-
axis. As can be seen upon review of Figure 9, as the MAP indicator 510 moves
up and down along the X-axis the area
520 becomes larger or smaller, respectively.
The process 535 then moves to a state 548 wherein the central venous pressure
of the patient is read. A
determination is then made at a decision state 550 whether the CYP has changed
since the last reading. If the CVP has
changed, the process 535 moves to a state 552 to determine whether the CUP has
increased or decreased. If the CVP has
decreased, the process 535 moves to a state 554 wherein the CVP indicator 515
is moved down. If a determination is
made at the decision state 552 that the CVP has increased, then the process
535 moves to a state 556 wherein the CVP
indicator 515 is moved up. The process 535 then moves to a state 558 wherein
the cardiac output (CO) is read.
A determination is then made at a decision state 560 whether the cardiac
output has changed since the last
reading. If the cardiac output has changed, the process 535 moves to a
decision state 562 to determine whether the
cardiac output has increased or decreased. If the cardiac output has
decreased, the process 535 moves to a state 564
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WO 99/39633 PCT/US99/02798
wherein the cardiac output indicator 524 is moved down along its Y-axis.
However, if a determination was made at the
decision state 562 that the cardiac output had increased, the process 535
moves to a state 568 wherein the cardiac
output indicator 524 is moved up along its Y-axis. The process 535 then moves
to a state 570 wherein the systemic
vascular resistance is measured.
A determination is then made at a decision state 572 whether the systemic
vascular resistance ISVR) has
changed since the last reading. If the SVR has changed, a determination is
then made at a decision state 574 whether the
SVR has increased or decreased since the last reading. If the SVR has
decreased, the process 535 moves to a state 578
wherein the SVR analog gauge 528 is moved to the right along its predetermined
arc. Thus, as the patient's vascular
resistance is decreased, the vascular resistor object 500 indicates a greater
area of outward flow. If a determination is
made at the decision state 574 that the SVR has increased, the process 535
moves to a state 580 wherein the SVR
analog gauge 528 is moved to the left along its predetermined arc. As
indicated in Figure 9, as the SVR analog gauge 528
moves to the left, the output area 521 of the vascular resistor object 500 is
reduced. The process 535 then terminates at
an end state 582.
D. The Metabolism Object
The metabolic factory graphical display object contains information regarding
oxygen delivery (D02) to cellular
factories (in aggregate), aerobic (oxygen burning) metabolic activity (oxygen
utilization or V02), and anaerobic metabolic
activity (using correlates suggestive of lactate production, in this case the
Base Deficitl. The data scales are arranged to
allow the oxygen supply to be compared to the indicators of utilization and
cellular well being.
Referring to Figure 11, a metabolism object 600 is illustrated. The metabolism
object 600 displays the
relationship of oxygen delivery (DOZ) by illustrating the equation: (Oxygen
Delivery) - (Cardiac Output) x (Arterial Oxygen
Content).
In addition, the metabolism object 600 also illustrates Oxygen Utilization
(VOZ) by the equation: (Oxygen
Utilization) - (Arterial Oxygen Content) - (Venous Oxygen contentl.
In a normal patient, the oxygen supply greatly exceeds the oxygen utilization.
Thus, a fulcrum or pivot 610 is
used to illustrate the balance between an oxygen supply (DOZ) indicator 620
and oxygen demand (V02) indicator 630. A
lever or balance line 640 runs between the DOZ indicator 620 and V02 indicator
630 and balanced on the pivot 640. The
slope of the D02 to VOZ is used to indicate the "balance" or relationship
between DOz and VOZ more readily apparent to the
physician . In addition, anaerobic metabolism and its associated acidosis
cause the scale to tip in the wrong direction to
indicate that although oxygen is being supplied, the cells are not using it.
Referring to Figure 12, a process 650 of updating the metabolism object 600 is
described. The process 650
begins at a start state 652 and then moves to a state 654 where the oxygen
supply of the patient's blood is read. The
process 650 then moves to a decision state 656 to determine whether the oxygen
supply value (D02) has changed since
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CA 02321227 2000-08-24
cc cc" e~ ~~ s~ «
the last readin . If the ox en su I value has than ed, the rocess 650 m~ves'~
4 ~ ' '' ~ ~ ~°~
g Yg PP y 9 P ,o a'-dec,sion stake ~5~to determine < <
cc c es s~ e' cc
whether the oxygen supply has increased or decreased in the patient's blood.
if the value of the oxygen supply has
' decreased, the process 650 moves to a state 660 wherein the oxygen supply
indicator 620 (Figure 11 ) is moved
downward along its Y~axis. However, if the oxygen supply value has increased,
the process 650 moves to a state 662
wherein the oxygen supply indicator 620 is moved upward along its Y~axis. The
process 650 then moves to a state
664 to read the oxygen demand value NOZ) in the patient.
Once the oxygen demand value has been read at the state 664, the process 650
moves to a state 666 to
determine whether the oxygen demand value has changed since the last reading.
If the oxygen demand value has
changed, the process 650 moves to a decision state 668 to determine whether
the oxygen demand value has
increased or decreased. If the oxygen demand value has decreased, the process
650 moves to state 670 wherein the
oxygen demand indicator 630 (Figure 11) is moved downward along its Y-axis.
However, if a determination is made at
the decision state 668 that the oxygen demand has increased, the process 650
moves to a state 672 wherein the
oxygen demand indicator 630 is moved upwards. The process 650 then terminates
at an end state 674
E. AiveoIarArteriaiPartialPressure Oxygen Gradient Object
As shown in Figure 14A, this graphical data display object 800 contains an
outline 802 suggestive of a lung
unit on the left, an outline 804 suggestive of an artery on the right, and a
scale 806 in~between which represents the
barrier to oxygen diffusion from lung to blood. A pointer 808 on the left,
inside the "lung" depicts partial pressure of
Alveolar oxygen using the Ideal Alveolar Gas Equation. A pointer 810 on the
right, inside the "artery" depicts partial
pressure of arterial oxygen. Trending is shown to the left. The normal
gradient, shown on the scale as a oreen region.
is based on accepted formulas (normal arterial oxygen is a function of the
fraction or inspired oxygen). The line
connecting the pointers represents the gradient.
f. Data Box Graphical Elements
An exemplary data box graphical element 900 is shown in Figure 14B. As shown
in this embodiment, data
boxes may have three sub~boxes: a numeric box 902, an alarm box 906 and a
trend box 904. The numeric box
contains the data value, the data label and the data units. The alarm box h_as
a reference scale, a value pointer, color
encoded (typically green on green) normal zones representing the upper and
'lower alarm limits (here 34 and 15).
Warning zones clinicians can set, are represented triangular regions. The
pointer and numeric box may change color
(i.e. to red) in a graded fashion as the value moves through the warning zone.
Confidence intervals for the data are
represented by linking the thickness of the pointer tip to the precision of
the measured variable. The trend box shows
the recorded value of the parameter over a selected period of time. It will be
appreciated that multiple data boxes
may be used in a single display to represent several relevant parameters.
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A~~~~U'~~ S~~
- i CA 02321227 2000-08-24
r cc cccc cc of ei. oe
~ G. Acid Base Graph Object ~ - _ '
/ t " ° c ecc a -ace oae
y ,_ c rc~ ~ ° ° c
cr oc ee4 e°
Figure 14C shows an exemplary acid-base object 950. Those skilled in the art
will appreciate that the acid-
base object represents the metabolic and respiratory components of the
Henderson-Hasselback relationship on an x, y
graph 952. Diagonal pH lines 954 are shown on the reference grid. Colored
markings are used to encode normal
zones 958, 956 and 960 for bicarbonate, partial pressure carbon-dioxide and pH
respectively. Using bicarbonate and
carbon~dioxide allows clinicians to see the two major components of the acid-
base system that they can treat (with IV
Sodium Bicarbonate and Ventilation changes respectively).
H, Grouping the Data Objects into a Unified Display
Figure 13 illustrates one embodiment of a display having each of the data
objects 300, 400, 500 and 600.
The data objects are arranged in the pattern shown to create a circuit
illustrating that oxygen is carried from the left
ventricle of the heart pump object 400, into an arterial blood cell 310a,
through the vascular resistor 500 (e.g.
capillary cells) where oxygen is unloaded at the tissue cells (object 600) and
returns to through a venous blood cell
310b to the right ventricle 440. Thus, a complete illustration of the
oxygenation cycle is p~nuidad in a vprv ~nr~~~tj~
manner by the relationship of objects in Figure 13.
._
I. Boundary information
All of the scales used to map values to indicators and gauges preferably have
normal and abnormal zones
(which can be and preferably are colored). Thus, the indicators can change
colors when a patient is entering an
abnormal zone. The alert zones are selectable so that the physician can make
the warnings more or less stringent
based on the physiology of the particular patient. In this manner, the user
sets the value above or below the critical
thresholds at the point she wishes to be alerted. When the alert zone is
entered, an indicator begins to change color, or
start flashing in a graded manner such that the brighter the red-color of the
indicator, the closer the value is to the
threshold. Of course, the indicators could change in many different ways to
alert the physician that an abnormal zone
has been entered. This invention should not be construed to be limited by any
particular notification method.
J. Confidence intervaiinformation
When the precision and bias of a measured data channel are known, the pointer
tip is preferably centered on
the appropriate value but will have a thickness which touches the scale and
which covers the know error associated
with that datum. This creates a pointer which changes color and which enters
danger zones based on worse case
scenarios.
K. Tread informatioo
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p,~IIENdE~ ~''~'~~i
CA 02321227 2000-08-24
.. .... .. .. .. ..
.. .. . . . . . . . . . .
The trend information, for example, includes a set of "cards" on a tads of orb
a tithe ~c~le do thls;X-axis'.': ":
.. . .. .. .. ..
The values over a time interval selected by the user are displayed and the
resolution of the data (sampling rate) is
made visible.
L. Normalization of Information.
Due to tremendous inter-patient variability and the changing patient
physiologic state in settings like surgery
(i.e., the definition of what is normal changes) the values which represent
frames of reference can be re-sized and re
scaled on command. For example, a "normal" SVR setting for the SVR object 550
of Figure 9 can default to 1000 at
the 3 o'clock position. However, if a patient normally has a SVR of 2000, this
function can reset the normal 3 o'clock
position of the SVR analog gauge to 2000.
M. Artifact Detection and Signal Quality Information.
Viewing the analog signal of a given data channel provides a great deal of
information about signal quality.
Pop-up windows next to the data pointers are thus available, similar to the
trend windows, to detect noise or artifact
information. The pop-up windows are activated by, for example, clicking on a
data pointer.
N. Patient Disease Information
The data regarding disease states can be saved, if desired. to reset boundary
defaults. For example,
hypertension shifts the autoregulatory curve to the right such that most
doctors keep the blood pressure in a higher
range than usual.
Pilot Studv
A pilot study was performed which attempted to test the hypothesis that the
set of object displays
developed will improve the ability of anesthesiologists to solve problems such
as acute hypotensian.
Study subjects: study subjects were all in their final year of-tteiflning or
attending level anesthesiologists
(N=10). Each physician had over three months experience providing cardiac
anesthesia.
34 ~,,~1EI~~~~' S'~~~'T
CA 02321227 2000-08-24
WO 99/39633 PCT/US99l02798
Test Parameters:
Data sets were generated for five patterns of shock lanaphylactic,
bradycardic, hypovolemic, cardiogenic, and
secondary to pulmonary embolus) and five patterns of near shock (MAP-CVP was
60-70mm Hg but otherwise were
represented the five shock states). The data sets were used to generate twenty
"flash cards" (one set standard display
cards and one set of graphical display cards). Figure 14 is an example of one
flash card from the study indicating
anaphylaxis.
Hardware consisted of a computer workstation with a 21 inch touch-screen
monitor. The study test was a
software application written in LabSliew. The application "shuffles" the cards
to randomize the order in which they are
presented to the study subject. When the application is started (constituting
a trial), a screen with a "next" button hides
the upcoming display. When the study subject touches this button, the first
display picture appears and the subject must
choose from five buttons tNo Problem, Anaphylaxis, Bradycardia, Hypovolemia,
Ischemia, and Pulmonary Embolus). The
"next" button screen then appears and touching the button advances the next
card. This is done for all twenty cards. The
internal clock in the computer is used to measure problem (shock) recognition
speed, accuracy and pattern recognition
(etiology) speed and accuracy. Study subjects completed surveys pre- and post-
testing.
We discovered that the residents were able to recognize problems 30 percent
faster in comparison to previous
displays. In addition, the residents were able to identify patient patterns
25% faster than with previous displays. We
found that there was no difference in accuracy. The total training time was
approximately 30 minutes.
Conclusion
Current displays for presenting physiologic data to physicians working in
critical care medicine force the
physicians to perform a great deal of cognitive work to interpret that data.
The display system disclosed herein provides
visual memory cues and maps complex data graphically to displays which match
the mental model physicians used to
interpret oxygen-transport physiology.
The system receives analog signals which drives the display real-time. Alarm
conditions can be set by the
physician and are visible at all times. The danger zones which create shades
of red in the data pointer are easy for
physicians to understand (physicians are accustomed to using fuzzy logic for
interpreting data). In addition, the way that
data elements have been constructed and displayed produces perceptual
diagrams. The shapes themselves convey very
high-level information regarding oxygen-transport physiology to physicians.
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