U.S. patent application number 14/043482 was filed with the patent office on 2014-02-20 for monitoring device and method.
This patent application is currently assigned to LiDCO Group PLC. The applicant listed for this patent is LiDCO Group PLC. Invention is credited to Terence Kevin O'Brien.
Application Number | 20140051051 14/043482 |
Document ID | / |
Family ID | 44858776 |
Filed Date | 2014-02-20 |
United States Patent
Application |
20140051051 |
Kind Code |
A1 |
O'Brien; Terence Kevin |
February 20, 2014 |
MONITORING DEVICE AND METHOD
Abstract
A monitoring device arranged to display a level of consciousness
and hemodynamic parameters of a patient for simultaneous viewing. A
dependence of changes in the hemodynamic parameters of the patient
on the level of consciousness of the patient may be more easily
observed using the monitoring device. Correlations between the
patient's level of consciousness and the patient's hemodynamic
parameters may further be determined and displayed to aid
clinicians in estimating any improvement in hemodynamic parameters
that may be achieved through manipulation of the patient's level of
consciousness, fluid status and drugs.
Inventors: |
O'Brien; Terence Kevin;
(Cambridgeshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LiDCO Group PLC |
London |
|
GB |
|
|
Assignee: |
LiDCO Group PLC
London
GB
|
Family ID: |
44858776 |
Appl. No.: |
14/043482 |
Filed: |
October 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12770856 |
Apr 30, 2010 |
8568327 |
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14043482 |
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Current U.S.
Class: |
434/268 ;
600/301; 604/503 |
Current CPC
Class: |
A61B 5/0205 20130101;
A61B 5/021 20130101; G09B 23/285 20130101; A61B 5/0476 20130101;
G16H 40/63 20180101; A61B 5/024 20130101; G06F 19/00 20130101; A61M
5/1723 20130101; A61B 5/4821 20130101; G16H 50/50 20180101; A61B
5/029 20130101 |
Class at
Publication: |
434/268 ;
600/301; 604/503 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61M 5/172 20060101 A61M005/172; G09B 23/28 20060101
G09B023/28; A61B 5/021 20060101 A61B005/021 |
Claims
1-14. (canceled)
15. A method of monitoring anaesthetic induction comprising using a
monitoring device to record a series of data sets over a period of
time, each data set comprising a value of a signal indicating a
level of consciousness of a patient or simulated patient applicable
at a time point and a value of said arterial blood pressure signal
applicable at the time.
16. A method according to claim 15, wherein said period of time
includes a period of time prior to the administration of an
anaesthetic and/or sedative, a period of time between the
administration of the anaesthetic and/or sedative and intubation
and a post intubation period.
17. A method of restoring blood pressure or blood flow of a patient
or of training to restore the blood pressure or blood flow of a
simulated patient following the induction of anaesthesia and/or
sedation, comprising: correcting a deviation in the level of
consciousness of the patient or simulated patient during
anaesthetic induction from a desired level; thereafter, if the
blood flow or blood pressure is below a target value, checking the
hydration level of the patient or simulated patient using a
monitoring device and administering one or more fluid challenges,
if the patient is determined, using the monitoring device, to be
hypovolemic; thereafter administering drugs potentially suitable
for changing the patient's blood flow or blood pressure towards the
target value in a staged manner to identify a suitable drug, if the
patient's or simulated patient's blood flow or blood pressure
monitored using the monitoring device deviates from the target
value.
18. A method of restoring blood pressure of a patient or of
training to restore the blood pressure of a simulated patient
following the induction of anaesthesia and/or sedation, comprising:
monitoring the level of consciousness of a patient or a simulated
patient using a monitoring device; adjusting an administration of
anaesthetic or sedative to the patient or simulated patient so that
the patient's or simulated patient's level of consciousness
determined by the monitoring is within a predetermined range; using
a monitoring device to determine if the patient is hypovolemic and
administering one or more fluid challenges if the patient is
determined to be hypovolemic; using a monitoring device to
determine if the patient's or simulated patient's systolic or mean
arterial blood pressure has reached a desired value and if the
patient's systolic or mean arterial blood pressure has not reached
the desired value determining, through staged application whilst
monitoring the patient's or simulated patient's blood pressure
using the monitoring device, whether a vasopressor acting
predominantly on the venous part of the patient's or simulated
patient's vascular system, a vasopressor acting predominantly on
the arterial part of the patient's or simulated patient's vascular
system and/or an inotropic drug is suitable for increasing the
patient's or simulated patient's blood pressure.
19. A method of restoring blood pressure of a patient or of
training to restore the blood pressure of a simulated patient
following the induction of anaesthesia and/or sedation, comprising:
displaying on a display an image showing a development in the
patient's or simulated patient's blood pressure level and of the
patient's or simulated patient's level over consciousness over time
and adjusting an amount of anaesthetic and/or sedative administered
to the patient or to the simulated patient until the level of
consciousness of the patient is within a predetermined target zone;
displaying, following intubation, on the display an image showing a
development in the patient's or simulated patient's blood pressure
level over time and an image of a variation in the patient's or
simulated patients left ventricular stroke volume and/or in the
patient's or simulated patients pulse pressure; deciding based on
the image of the variation in left ventricular stroke volume and/or
pulse pressure whether or not the patient is likely to be
hypovolemic and, if so, administering a fluid challenge, if a
current blood pressure has not reached a desired value; displaying
on the display an image of a change in the patient's or the
simulated patient's stroke volume over time, following an
administration of the said fluid challenge; determining if the
patient's or the simulated patient's blood pressure has reached the
desired value and, if the patient's or the simulated patient's
blood pressure has not reached the desired value, identifying,
through staged application, a drug that is suitable to increase the
patient's or simulated patient's blood pressure.
20. A method according to claim 19, further comprising setting a
marker at the time of an intervention and deciding whether or not
the intervention has affected the observed change in mean arterial
blood pressure.
21. A portable non-volatile memory device having stored thereon a
series of values representing a patient's level of consciousness at
different points in time and a series of arterial blood pressure
values at the different points in time.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus and method for
hemodynamic monitoring. The present invention in particular relates
to an apparatus and method suitable for hemodynamic monitoring
during surgery, sedation/anaesthesia and/or induction of
sedation/anaesthesia.
BACKGROUND
[0002] It is known that the blood pressure of surgery patients
falls from a pre-anaesthetic induction level to a lower level
during induction of sedation/anaesthesia.
[0003] This reduction in blood pressure has to be corrected by the
anaesthetist to at least a level that is likely to reliably support
the patient's vital functions.
[0004] The drop in blood pressure through the anaesthetic induction
phase is widely viewed as being the result of a fall in systemic
vascular resistance (SVR; SVR=[((mean arterial pressure-central
venous pressure)*80)/cardiac output)]; the unit normally used for
expressing SVR is dynes*s*cm-5) due to the administered anaesthetic
drug(s) causing a vasodilatory response of the arterial tree. The
arteries and pre-capillary arterioles provide about two thirds of
the resistance to flow in the vascular system. Arterial
vasodilation increases arterial capacity and consequently reduces
the affected vasculature's resistance to blood flow. As the mean
arterial pressure (MAP) is the product of cardiac output (CO) and
systemic vascular resistance (MAP=CO*SVR), a reduction in SVR
brings about a corresponding blood pressure reduction if the
cardiac output remains the same.
[0005] While a fall in blood pressure can be caused by arterial
vasodilation and the above discussed associated decrease in
systemic vascular resistance, a number of other factors also
influence blood pressure. Changes in cardiac output can also affect
blood pressure/MAP. Cardiac output (expressed in l/min) is the
product of stroke volume (SV, expressed in ml) and heart rate (HR,
expressed in bpm). A fall in heart rate will therefore reduce
cardiac output and arterial blood pressure.
[0006] Cardiac stroke volume in turn is affected by a number of
factors. One of these factors is the extent to which the left
ventricle is filled before contraction. This factor is often
referred to as preload. In the healthy heart the fuller the
ventricle is before systole (contraction) the more that the ejected
stroke volume will increase--up to a limit, as can be seen from the
Frank Starling curve. The dependence of the filling of the left
ventricle on the efficient venous return of blood to the right side
of the heart is often referred to as preload dependence. If the
venous blood flow to the heart is insufficient to adequately fill
the left ventricle prior to its contraction, then the stroke volume
is reduced.
[0007] The major collecting veins contain 64% of the total
circulating blood volume. The diameter and tone of the major
collection veins is adjusted through hormonal/neural effects on the
vein's smooth muscle component. Drugs may influence the major
collection veins' tone and capacitance. Dilation of the major
collection veins and/or blood loss will reduce preload and
consequently also stroke volume.
[0008] Another factor affecting blood pressure is the resistance to
the ejection of blood from the left ventricle across the aortic
valve into the systemic arterial circulation. This resistance can
be considered the sum of all forces opposing ventricular muscle
shortening. This factor is often referred to as afterload and is
regularly (and incorrectly) considered to be the same/similar to
systemic vascular resistance (SVR). A simple example can show that
afterload and SVR are in fact not the same. If two patients with
equal ventricular dimensions are considered, wherein the first
patient has a MAP of 60 mmHg and a cardiac output of 4 l/min and
the second patient has a MAP of 120 mmHg and a cardiac output of 8
l/min. Both of these patients will have the same SVR. The
resistance to the ejection of blood from the left ventricle,
however, differs by a factor of two, as is evident from the
difference in MAP.
[0009] If the left ventricle is working in a preload dependent
fashion then the ventricular internal fibre load applied during
systole does not compromise the stroke volume ejected. In this case
the patient's hemodynamic performance is deemed afterload
independent. However, increases in afterload are poorly tolerated
in patients with no preload reserve (at the top of Frank Starling
curve, that is patients that could be fluid overloaded) and/or
those patients with left ventricular systolic dysfunction.
[0010] Blood pressure is moreover affected by the heart's
contractility. The term `contractility` refers to the inotropic
state of the left ventricular myocardium, that is the force and
velocity with which the myocardial fibres contract with each heart
beat. In clinical practice a variety of contraction-phase
indices/parameters such as the velocity of fibre shortening, peak
rate of ventricular pressure rise and the end-systolic pressure to
volume relationship are in use. The inotropic state of the left
ventricle can be changed/supported by the administration of an
inotropic drug such as adrenaline. Low contractility and high
afterload will reduce stroke volume.
[0011] U.S. Pat. No. 6,071,244 and US patent application US
2009/0131805, the entireties of which are herein incorporated by
this reference, disclose hemodynamic monitors for determining
stroke volume based on arterial blood pressure measurements.
[0012] The positive pressure in the thoracic cavity of patients on
a respirator can affect the stroke volume of the patient's heart.
US patent application US 2009/0131805 discloses that the necessary
variations in this pressure can cause considerable variations of
stroke volume over a respiratory cycle. US 2009/0131805 recognises
that this is particularly the case for hypovolemic patients and
proposes to use the degree of variation in stroke volume over a
respiratory cycle as an indication of the hemodynamic status.
[0013] A major limitation in displaying parameters on screen in a
clinical environment, in particular in operating theatres is that
the space available for any kind of display is severely limited. At
the same time, however, the display has to be fashioned so that the
displayed information can be intuitively understood, even if the
observer is not close to the display.
SUMMARY OF THE INVENTION
[0014] According to an aspect of the present invention there is
provided a monitoring device comprising a part for acquiring a
signal indicating a level of consciousness, a part for acquiring an
arterial blood pressure signal, a display and a processor or
processors. The processor or processors are arranged to cause the
display to display, for simultaneous viewing, an image showing the
blood pressure signal over time, an image showing cardiac output or
stroke volume over time, an image showing systemic vascular
resistance over time and an image showing the level of
consciousness over time based on the signal indicating the level of
consciousness. The cardiac output, the stroke volume and the
systemic vascular resistance can be determined at least partially
based on the arterial blood pressure signal.
[0015] The inventors have found a relationship between the depth of
anaesthesia/level of consciousness during anaesthesia and the
hemodynamic parameters of the patient. Although the strength of
this relation was found to vary between patients, lower levels of
consciousness were found to be associated with decreased blood flow
and pressure. Based on these findings the inventors have realised
that simultaneous monitoring of the patient's blood pressure,
cardiac output, systemic vascular resistance, blood pressure and
fluid responsiveness (by monitoring stroke volume variations or
pulse pressure variations in patients on a respirator), while
maintaining and limiting anaesthesia depth/the patient's level of
consciousness to pre defined targets, should allow finer
discrimination and more efficient control of the patient's
hemodynamic changes.
[0016] The above discussed monitoring device allows simultaneous
observation of the level of consciousness of a patient and of the
hemodynamic parameters of the patient that can be quantified prior
to intubation, namely blood pressure, cardiac output or stroke
volume, heart rate and systemic vascular resistance, and to allow
the user to correlate changes in these parameters to changes in the
patient's level of consciousness by observing the display. This is
particularly useful during the induction phase of
sedation/anaesthesia, during which, as discussed above, drastic
changes in the hemodynamic parameters can occur.
[0017] The display for simultaneous viewing can, for example, be
such that the above mentioned images are the only images that
displayed on the display. A display of this nature is advantageous
as it permits the displayed images to be as large as the size of
the display area or of a part of the display area allocated for the
display of the above mentioned parameters, thereby aiding in
guiding an observer to the relevant displayed information. An
arrangement of this nature also helps in keeping the required size
of a display small, therefore saving valuable space in the
operating theatre. Displaying numbers alongside such images can
help in quickly ascertaining a current value of a parameter that
may also be displayed in the form of an image or another parameter
that may not be displayed in the form of images. The images may
occupy a majority, for example more than 70% or more than 80% of
the available/allocated display area.
[0018] The present invention is, however, not limited to monitoring
devices that only display the above mentioned images. If it is
acceptable to use a larger size display as part of the monitoring
device, or if it is acceptable to display the images in a smaller
format, then other images (or, more generally, items) can be
displayed on the display.
[0019] In this case the display of the images should nevertheless
be such that information displayed to the observer is readily
accessible to the observer through its presentation. This can be
achieved by grouping the above mentioned images together, so that
observer is not disturbed/distracted by other information that may
be provided between the images. Put in other words, the images can
be displayed in a contiguous fashion/by placing them in contiguous
display panels. Some of the images can of course be superimposed
over each other, as long as the aim of presenting the images for
simultaneous viewing is still fulfilled. The display panels may
also comprise components presented in number format, where the
display of such components aids the observer in assessing the
displayed images. The above mentioned display of current values of
parameters in number format is one example of this.
[0020] According to another aspect of the present invention there
is provided a monitoring device comprising a part for acquiring a
signal indicating a level of consciousness, a part for acquiring an
arterial blood pressure signal, a display and a processor or
processors. The processor or processors are arranged to cause the
display to display, for simultaneous viewing, an image showing the
blood pressure signal over time, an image showing cardiac output or
stroke volume over time, an image showing systemic vascular
resistance over time and either, in one operating mode, an image
showing the level of consciousness over time based on the signal
indicating the level of consciousness, or, in another operating
mode, an image showing a variation in stroke volume, a variation in
pulse pressure (systolic--diastolic arterial pressure) and/or a
pleth variability (pulse oximeter waveform amplitude) index. The
cardiac output, the stroke volume, the systemic vascular
resistance, stroke volume variation and pulse pressure variation
can be determined at least partially based on the arterial blood
pressure signal.
[0021] The monitoring device may, instead of or in addition to
providing a function for switching between a display of the level
of consciousness and the display of a variation in stroke volume or
pulse pressure may provide a simultaneous display of the level of
consciousness and the display of a variation in stroke volume or
pulse pressure or pleth variability index, if the available screen
size allows such a display. In either case the monitoring device
allows observing the level of hydration of the patient (by
observing stroke volume and/or pulse pressure variations, or pleth
variability index) as well as the level of consciousness, either
simultaneously, or through the simple activation of a toggle switch
that may be provided on the monitoring device, for example in the
form of an icon displayed on a touch sensitive screen. This
monitoring device is particularly advantageous post intubation,
when meaningful data on stroke volume variation and/or pulse
pressure variation or the pleth variability index are
available.
[0022] It has been recognised that the replacing of a displayed
images with an image showing the patient's response to an
intervention can provide further useful information to the
clinician. To facilitate such a display the processor can be
further arranged to, in an operating mode other, than the above
described operating modes, replace the display of one of the said
images with the display of an image showing a response of a
hemodynamic parameter to an intervention. The image showing the
response may provide a display of a percentage change in the
parameter, relative to the level of the parameter immediately prior
to the intervention. The image may display a change in cardiac
output, stroke volume, systemic vascular resistance or systolic or
mean arterial blood pressure. The processor may be arranged to
retain the image showing the absolute values of systolic or mean
arterial blood pressure over time and/or an indication of the
patient's heart rate on the display.
[0023] Either of the above discussed displays avoids a need for
clinicians to observe different monitoring devices and/or a need to
change between different displays of a particular monitoring
device. This is advantageous because the sole/isolated monitoring
of blood pressure does not allow identification of determinants of
a pressure drop and of their relative contributions to a blood
pressure change. The monitoring device of the present invention is
thus more user friendly than other monitoring devices. It will be
appreciated that this can be of critical importance as it reduces a
need for clinicians to alter parameters displayed on the monitoring
device while dealing with potentially critical situations.
[0024] The inventors have moreover found that, as the patients'
hemodynamic response to anaesthesia is complex and individual to
the patient and cannot be fully understood by blood pressure
monitoring alone, it is inadvisable for a standard protocol aimed
at restoring blood pressure and/or blood flow to be followed.
Instead therapeutic approaches to the restoration of the patient's
blood pressure and/or blood flow and/or oxygen delivery should be
informed approaches, targeted to eliminate or at least reduce
factors limiting the restoration in the patient's blood pressure
and/or blood flow. Any such approaches may be staged, so that
different factors are addressed one at a time and/or in a gradual
fashion. If a clinician determines, for example based on the
display of systemic vascular resistance, that the patient's
systemic vascular resistance or the patient's afterload impedes
cardiac output, then the clinician may decide to administer a
vasodilator that causes a reduction in arterial tone. The effects
of the administration of such a vasodilator can be observed through
the display of the patient's hemodynamic parameters on the display.
Alternative or additional interventions can be undertaken if the
administration of the vasodilator is noted as being ineffective or
insufficiently effective. Vasodilators may alternatively be used to
cause a decrease in venous tone to reduce preload and, as a
possible consequence, stroke volume. The net effect of such use of
vasodilators is the resultant balance between the reduction in
afterload, systemic vascular resistance and preload and can be
observed using either of the above discussed monitoring devices. If
such observation shows that a reduction in arterial tone is
effective in improving the patient's hemodynamic parameters, then
such a reduction in arterial tone may be further promoted by the
clinician, for example through the administration of arterial
vasodilator. If venous vasodilation predominates then a drug having
emphasised venous tone effects may be more suitable. If another
observation suggests that arterial vasoconstriction may be
desirable, for example for increasing blood pressure by increasing
arterial tone, then the choice of the type of vasoconstrictor to be
administered may be important as some vasoconstrictors may have a
more pronounced effect on the arterial, rather than venous tone.
Inotropes may be administered to increase ventricular muscle
contractility.
[0025] It will be appreciated that the aim of restoring blood
pressure and blood flow is to ensure that the patient's tissue is
sufficiently oxygenated. In addition to the amount of blood
reaching the tissue and the ease with which the blood flow reaches
the tissue a factor determining oxygenation is the amount of
saturated haemoglobin available in the blood for oxygen delivery.
If blood haemoglobin values are low, then it will likely be
desirable for blood flow to be increased. It will be appreciated
therefore that knowledge of blood haemoglobin levels, and of the
degree of saturation of the haemoglobin in the blood, is
advantageous. The monitoring device may comprise an input for
inputting an indication of the blood haemoglobin level, of the
saturation of the available haemoglobin and/or of the blood oxygen
content for this purpose, for example in the form of a graphical
user interface allowing the entry of the relevant values, or in the
form of a input arranged to receive a signal representative of any
such values from another measurement device. The processor may be
arranged to increase a target value for blood flow to account for
low blood haemoglobin levels or for a change in haemoglobin and/or
saturation levels from a haemoglobin/saturation level at the start
of monitoring or at the start of a surgical procedure or a target
value.
[0026] The inventors have found that restoring normovolemia and
ensuring adequate, but not excessive, anaesthesia is a big step
towards better control of the patient's blood pressure/hemodynamic
status during surgery. The monitoring device of the present
invention is suitable for aiding clinicians in this dual aim. It
was also found that being able to identify those parameters of the
hemodynamic parameters and the level of consciousness that should
not be manipulated to restore adequate blood pressure or blood flow
or that, even if manipulated, will not lead to an improvement in
blood pressure or blood flow is advantageous as the identification
of such parameters can prevent the administering of a fluid
challenge or drugs that would fail to remedy a reduction in blood
pressure in an efficient or effective manner or that may even be
detrimental to the state of the patient. It can, for example be
envisaged that a patient's systemic vascular resistance has not
changed significantly over the course of anaesthetic induction. Any
decrease in blood pressure is thus likely to be caused by a
decreased cardiac output. This suggests that drugs increasing
systemic vascular resistance are contraindicated, as they are
likely to increase afterload and may decrease blood flow further
without appreciable positive effect.
[0027] The monitoring device of the present invention can aid
clinicians in identifying likely causes of a reduction in blood
pressure and in identifying associated suitable remedies for such
reductions as well as unsuitable ways of seeking to remedy such
reductions. The monitoring device of the present invention thus
affords anaesthetists fuller control of the depth of
anaesthesia/level of consciousness and fluid status of the
patient.
[0028] The monitoring device of the present invention can
facilitate identification and possibly even quantification of the
drivers behind changes in blood pressure during anaesthetic
induction by displaying the above discussed parameters. The
monitoring device of the present invention can further facilitate
monitoring the efficiency of measures taken by clinicians to
correct blood pressure (and level of consciousness) to target
levels by displaying such target levels. Such target values may,
for example, correspond to, or close to the values the hemodynamic
parameters or blood pressure had pre-induction. If, for example, a
patient is assessed to have sufficient blood flow prior to a
(surgical) intervention, then this level of blood flow may be used
as a good blood flow target if the patient's blood oxygen content
level remains unchanged. The use of target values that are based on
pre-induction levels of blood pressure or of a hemodynamic
parameter allows the use of the monitoring device for displaying
relative change, without a need to calibrate the monitoring device
for the display of absolute values.
[0029] Alternatively any such target values may be predetermined
values. The use of predetermined values can be particularly
advantageous in situations where the pre-induction values are
unsuitable target values, for example for patients that are
normally hypertensive. Providing target values for blood pressure
and cardiac output is particularly advantageous and the monitoring
device may be arranged to provide target values for blood pressure
and cardiac output.
[0030] Optimising blood flow parameters during surgery in an
informed/targeted fashion has been shown to improve the outcome of
surgery. It has in particular been shown that the side effects
suffered by patients following surgery can be reduced.
[0031] Consequently the length patients have to stay in hospital
post surgery can also be reduced.
[0032] The signal indicating the level of consciousness may be a
biopotential signal or based on a biopotential signals. The
biopotential signals can, for example, be EEG signals that can be
used as the basis for determining the indication of the level of
consciousness of the patient from which the biopotential signals
have been derived. The monitoring device may comprise a means for
determining a level of consciousness from the biopotential signals.
Alternatively, the signal indicating a level of consciousness may
be received from a device provided outside of the monitoring
device. The signal may thus be an output signal of a device that
determines the level of consciousness, for example based on the
above mentioned biopotential signals. Such an output signal may,
for example, be a bispectral index signal. In this case the part
for acquiring a signal indicating a level of consciousness of the
monitoring device may be a simple input (connector) arranged to
receive a connection/cable or wireless transmission from the device
that determines the level of consciousness. One suitable external
device for determining the level of consciousness is Covidien's
Bispectral Index (RTM) device (Covidien plc, Cherrywood Business
Park, Loughlinstown, Co. Dublin, Ireland). Another such device is
the SEDline Brain Function Monitor (SEDline, Irvine, Calif., USA).
The part for acquiring a signal indicating a level of consciousness
may also comprise an analogue to digital converter, if any signal
received from an external device is an analogue signal.
[0033] The processor(s) may further be arranged to display a target
level for the depth of anaesthesia/level of consciousness and/or to
provide an indication of whether or not the level of
consciousness/depth of anaesthesia is within a predetermined range.
This predetermined range may be a range that is known as indicating
a level of consciousness that prevents post surgical
recall/awareness, while not being lower than necessary for the
purpose of preventing post surgical recall. If the level of
consciousness/depth of anaesthesia is measured using bispectral
index, an appropriate range can be between 40 and 60.
[0034] U.S. Pat. No. 6,071,244, US patent publication number US
2009/0131805 and co-pending UK patent application no. 1002331.5
disclose methods of determining the left ventricular stroke volume
of a patient based on the patient's arterial blood pressure. The
documents and the methods disclosed therein are incorporated
expressly herein by this reference and can be used for determining
a stroke volume for display in embodiments of the present
invention. Cardiac output can be calculated as the product of
stroke volume and heart rate. The heart rate itself can be directly
derived from the arterial blood pressure signal or, alternatively,
can be provided via an external input of the monitoring device, for
example from an ECG apparatus. The mean arterial pressure can also
be directly derived form the arterial blood pressure signal in
known ways. Systemic vascular resistance can then be calculated as
the ratio of mean arterial pressure and cardiac output.
[0035] Changes in stroke volume may be monitored over a number of
heart beats, for example so that the changes in stroke volume over
one or more respiratory cycles can be evaluated. It is normal for
stroke volume to vary over a respiratory cycle of a ventilated
patient because the thoracic pressure of the patient changes. Large
variations in stroke volume can indicate that the patient is
hypovolemic. A display of changes in stroke volume can thus aid
clinicians in determining whether or not a patient is hypovolemic.
The patient's hydration status can also be determined by measuring
the patient's pleth variability index. A suitable device for
determining this index is the Masimo Rainbow SET SpHb total
haemoglobin measurement (Masimo, Irvine, Calif.).
[0036] The part for acquiring the arterial blood pressure signal
may generate the arterial blood pressure signal based on a signal
received from a sensor or may include the sensor itself.
Alternatively the part for acquiring the arterial blood pressure
signal may be an input for receiving a signal from a device that
generates such a signal. One device suitable for this purpose are
the invasive arterial pressure monitoring systems available from
LiDCO Ltd. of 16 Orsman Road, London, N1 5QJ, UK, such as the
LiDCOrapid or LiDCO.TM. plus hemodynamic monitors.
[0037] The processor(s) may, in addition to causing the display to
display images of the above mentioned parameters, display a current
value of one or more of the parameters that are being displayed in
the form of images, alongside the corresponding image. This further
clarifies the display. It is particularly envisaged that the
current value of the level of consciousness of the patient is
displayed alongside the image of the stroke volume variation or
pulse pressure variation or pleth variability index if the
monitoring is arranged to toggle between displaying an image of the
level of consciousness and an image of the stroke volume or pulse
pressure variation or pleth variability index.
[0038] It is moreover envisaged that present and past values of the
level of consciousness, in arrangement where it is not displayed in
the form of a separate image, are superimposed in number format
over one of the images displayed on the display. The past and
present values of the level of consciousness can advantageously be
displayed at the correct time point/the time point at which they
occurred, so that the indication of the level of consciousness is
provided alongside a substantially simultaneously
acquired/determined hemodynamic parameter.
[0039] This has been recognised as being advantageous sin its own
right and according to another aspect of the present invention
there is provided a monitoring device comprising a part for
acquiring a signal indicating a level of consciousness, a part for
acquiring an arterial blood pressure signal, a display and a
processor or processors. The processor or processors are arranged
to cause the display to display one or more of an image showing the
blood pressure signal over time, an image showing cardiac output or
stroke volume over time and an image showing systemic vascular
resistance over time. The processor or processors are moreover
arranged to cause the display to display values of the level of
consciousness in number format superimposed over a said displayed
image, at time points in the image at which the values of the level
of consciousness had occurred.
[0040] The displayed images may plot the level of consciousness or
the above discussed hemodynamic parameters over time. The images
may be displayed so as to be time synchronised with each other. A
display of this nature enables the user to detect simultaneous
changes in the level of consciousness and in one or more
hemodynamic parameters more easily. An identification of any such
simultaneous changes may help in identifying the cause for the
changes and in determining an appropriate way of countering any
undesired changes more reliably and quickly.
[0041] A display of the change in stroke volume may be a display of
the percentage change of stroke volume over a period of time. Such
a display can be in number format. The change in stroke volume can
alternatively or additionally be displayed in the form of a curve
plotting stroke volume one a per beat basis over time. A range of
stroke volume values centred on the mean stroke volume and
indicating upper and/or lower threshold beyond which a variation in
stroke volume is indicative of a hypovolemic state of the patient
may further be superimposed over any such curve for easy
visualisation of excessive variations in stroke volume.
[0042] The operation of the processor may be based on software code
stored in the monitoring device.
[0043] The monitoring device may further comprise a memory for
storing one or more of the signal indicating a level of
consciousness, the indication of the level of consciousness, the
arterial blood pressure signals and a one or more of the above
mentioned hemodynamic parameter that may be derived from the blood
pressure signal. Storage of one or more of these parameters is
useful for patient care, for example for a post operative review of
the anaesthetic procedure and/or the hemodynamic condition of the
patient.
[0044] Storage of these values can moreover permit analysing any
correlation between the stored values and the monitoring device can
be arranged to analyse stored data values to identify any such
correlation. The monitoring device may be arranged to display an
identification of any such correlation on the display. Identified
correlations can be useful for predicting any future changes in the
hemodynamic parameters of the patient. The monitoring device may,
for this purpose, display on the display a value indicating a
change or improvement that is likely to be achieved if a
hemodynamic parameter or the level of consciousness is changed by a
given amount. This can provide a prediction of a change in systolic
or mean arterial blood pressure that is likely achievable from one
or more of a change in the level of consciousness of the patient, a
change in cardiac output, a change in stroke volume, a change in
heart rate and a change in systemic vascular resistance. Such a
prediction can be obtained by interpolating between previously
obtained values. For example, the fitting of a characteristic curve
to previously, obtained pairs of values of the level of
consciousness of a particular patient and of the systolic or mean
arterial blood pressure of the patient may provide an indication of
the increase in systolic or mean arterial blood pressure that can
be achieved by increasing the level of consciousness of the patient
by an amount chosen by a clinician. If, for example, a linear
function can be fitted/is fitted to stored values, then the slope
of this function may be displayed (in number format and/or by
displaying the curve with the correct slope) to provide the
clinician with an indication of potentially achievable gains A
linear function may for example be fitted to a series of data sets
comprising values indicative of the patient's level of
consciousness and blood pressure values. Displaying the slope of
this function can inform the clinician of a likely increase in
blood pressure that would be achieved by increasing the level of
consciousness by a predetermined value, such as a unit value. The
monitoring device may thus provide the clinician with information
of a likely achievable increase in systolic or mean arterial blood
pressure if an amount of anaesthetic agent that is administered to
the patient is reduced. This is particularly useful in cases where
a current level of consciousness is lower than is required for the
purpose of the procedure the patient is subjected to. An increase
in systolic or mean arterial blood pressure value achieved or
achievable in this way/by increasing the level of consciousness of
the patient to a level that, while higher than a current level, is
still sufficiently low to be suitable for the procedure/operation
the patient is being subjected to may be such that further
intervention may not be required and can therefore be avoided.
[0045] It will be appreciated that, if the dependence of blood
pressure or another hemodynamic parameter on the level of
consciousness of the patient is strong (that is if the above
mentioned slope is steep), then changes in the level of
consciousness will likely affect blood pressure or the other
hemodynamic parameters strongly. In this case it is advantageous
for the level of consciousness to be displayed more prominently on
by the monitoring device. The processor(s) may therefore be
arranged to display the level of consciousness in a more prominent
manner if the slope (or its absolute value) exceeds a predetermined
threshold. The processor(s) may for example cause a display of an
image of the level of consciousness over time instead of only a
number indicating the current level of consciousness in this case,
or suggest changing the display in this manner to the user.
[0046] The memory may be provided internally of the monitoring
device and/or in the form of a removable memory. Such a removable
memory may be provided in the form of a card for receipt in a
receptacle of the monitor. A card of this nature can be patient
specific so that it may be kept with the patient's file once it is
no longer needed for monitoring the patient.
[0047] Recording a series of data sets and using the recorded data
sets to provide a curve characteristic for the patient has been
recognised as being advantageous in its own right. According to
another aspect of the present invention there is provided a
monitoring device comprising a part for acquiring a signal
indicating a level of consciousness, a part for acquiring an
arterial blood pressure signal a display and a processor or
processors arranged to record a series of data sets over a period
of time. Each data set comprises at least a value of the signal
indicating a level of consciousness at a time point and one or more
of a value of the arterial blood pressure signal at the time point
and a hemodynamic parameter or hemodynamic parameters determined
based on the blood pressure signal. The processor or processors are
further arranged to determine, based on the series of data sets, a
characteristic of one or more of a change in mean or systolic
arterial blood pressure, in systemic vascular resistance, in
cardiac output, in stroke volume, in stroke volume variation and in
pulse pressure variation dependent on the level of
consciousness.
[0048] The processor or processors can further be arranged to cause
the display to display one or more of the characteristics and an
indication of a change in blood pressure that is to be expected,
based on the characteristics, for a unit change in the displayed
level of consciousness.
[0049] The monitoring device may further be arranged to time stamp
the arterial blood pressure signal and/or the signal indicating a
level of consciousness. Using time stamped signals allows collating
signals obtained or received substantially simultaneously in data
sets. The monitoring device may be arranged to interpolate between
the data sets, for example by fitting a mathematical function to a
series of data sets. The series of data sets can span one or more
of a range of states of consciousness, a range of systolic or mean
arterial blood pressure values, a range of stroke volume values, a
range of heart rates, a range of systemic vascular resistance
values and a range pf cardiac output values. The processor(s) can
be arranged to use the mathematical function, once fitted, as the
characteristic curve of the patient from which the data has been
obtained. The processor(s) can derive predictions of a change in
hemodynamic parameters and/or in the systolic or mean arterial
blood pressure that can likely be achieved by altering one or more
of the level of consciousness of the patient or one or more of the
hemodynamic parameters. The processor(s) can, for example derive
predictions of a likely change in systolic or mean arterial blood
pressure achievable by an induced change in the systemic vascular
resistance, cardiac output and/or level of consciousness. The
mathematical function fitted may be a linear function.
[0050] The monitoring device may enable a user to input the
occurrence of an event, such as, for example, the beginning of the
induction of sedation/anaesthesia, the beginning of ventilation,
the start of a surgical procedure or a time point at which a drug
or fluid challenge is administered. The processor(s) may be
arranged to display markers on an image displayed by the display,
indicating the correct time point of the event alongside or
superimposed over data in the images. The monitoring device may
comprise an input means that allows the user to indicate to the
monitoring device that a relevant event has occurred. Such an input
means may be arranged to also enable the user to specify the nature
of the event.
[0051] The processor may moreover be arranged to display two images
of any (or all) of the above mentioned parameters, wherein one of
the two images displays the change/trend in the parameter over one
(longer) time period/axis, while the other image displays the
change/trend in the parameter over a shorter time period. A display
of this nature facilitates the identification of long term trends
in changes in the parameter in the first image as well as a more
detailed analysis of more recent or acute changes in the second
image. It is, for example, envisaged that the processor can be
arranged to provide a long term display of one or more of systolic
or mean arterial blood pressure, heart rate and stroke volume
alongside a corresponding shorter term display of the corresponding
parameter or parameters.
[0052] While the present invention has been described with
reference to a monitoring device, the present invention is not
limited thereto. The present invention also extends to methods of
monitoring a patient as well as methods of training to monitor a
patient. According to another aspect of the present invention there
is provided a method of monitoring anaesthetic induction comprising
recording a series of data sets over a period of time. Each data
set comprises a value of a signal indicating a level of
consciousness of a patient or simulated patient applicable at a
time point and a value of said arterial blood pressure signal
applicable at the time.
[0053] The period of time includes a period of time prior to the
administration of an anaesthetic and/or sedative, a period of time
between the administration of the anaesthetic and/or sedative and
intubation and a post intubation period.
[0054] According to another aspect of the present invention there
is provided a method of restoring blood pressure or blood flow of a
patient or of training to restore the blood pressure of a simulated
patient following the induction of anaesthesia and/or sedation. The
method comprises correcting a deviation in the level of
consciousness of the patient or simulated patient during
anaesthetic induction from a desired level. This correction may
improve the patient's blood pressure. If any such improvement is
insufficient, the hydration level of the patient or simulated
patient is considered and one or more fluid challenges are
administered, if the patient is determined to be hypovolemic. If
the patient's or simulated patient's blood flow or blood pressure
remains below a desired target, a suitable drug is determined by
administering potentially suitable drugs in a staged manner.
[0055] According to another aspect of the present invention there
is provided a method of restoring blood pressure or blood flow of a
patient or of training to restore the blood pressure of a simulated
patient following the induction of anaesthesia and/or sedation. The
method comprises adjusting the administration of anaesthetic or
sedative to the patient or simulated patient so that the patient's
or simulated patient's level of consciousness is within a
predetermined range, determining if the patient is hypovolemic and
administering one or more fluid challenges if the patient is
determined to be hypovolemic. The method comprises further
determining if the patient's or simulated patient's systolic or
mean arterial blood pressure has reached a desired value and, if
the patient's systolic or mean arterial blood pressure has not
reached the desired value determining, through staged application,
whether a vasopressor acting predominantly on the venous part of
the patient's or simulated patient's vascular system, a vasopressor
acting predominantly on the arterial part of the patient's or
simulated patient's vascular system and/or an inotropic drug is
suitable for increasing the patient's or simulated patient's blood
pressure and/or blood flow.
[0056] According to another aspect of the present invention there
is provided a method of restoring blood pressure and/or blood flow
of a patient or of training to restore the blood pressure and/or
blood flow of a simulated patient following the induction of
anaesthesia and/or sedation. The method comprises displaying on a
display an image showing a development in the patient's or
simulated patient's blood pressure level and of the patient's or
simulated patient's level over consciousness over time and
adjusting an amount of anaesthetic and/or sedative administered to
the patient or to the simulated patient until the level of
consciousness of the patient is within a predetermined target zone.
Following intubation an image showing a development in the
patient's or simulated patient's blood pressure level over time and
an image of a variation in the patient's or simulated patients left
ventricular stroke volume and/or in the patient's or simulated
patients pulse pressure and/or in the patient's or simulated
patients pleth variability index is displayed on the display. It is
then decided, based on the image of the variation in left
ventricular stroke volume, pulse pressure and/or pleth variability
index whether or not the patient is likely to be hypovolemic and,
if so, administering a fluid challenge, if a current blood pressure
has not reached a desired value. An image of a change in the
patient's or the simulated patient's stroke volume over time is
displayed following an administration of the said fluid challenge.
It is then determined if the patient's or the simulated patient's
blood pressure has reached the desired value and, if the patient's
or the simulated patient's blood pressure has not reached the
desired value, a drug that is suitable to increase the patient's or
simulated patient's blood pressure is determined, through the
staged application of various drugs that could be suitable. Drugs
having a shorter term effect may be applied before drugs having a
longer term effect, to avoid superimposing the effects of two drugs
and thereby rendering attributing a change in the patient's
condition to a particular drug difficult.
[0057] A marker may be set at the time of an intervention. Based on
the position of the marker in displayed image, it can be decided
whether or not the intervention has affected the observed change in
systolic or mean arterial blood pressure or blood flow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] Embodiments of the present invention will be described in
the following by way of example only and with reference to the
accompanying drawings, in which:
[0059] FIG. 1 shows an architecture of a hemodynamic monitor of an
embodiment;
[0060] FIG. 2 shows the results of a study in which hemodynamic
parameters of a patient and the patient's level of consciousness
have been monitored;
[0061] FIG. 3 shows the correlation between monitored hemodynamic
parameters and level of consciousness of the study results of FIG.
2;
[0062] FIG. 4 shows a display of one embodiment;
[0063] FIG. 5 shows a further display panel that can be included in
a display;
[0064] FIG. 6 shows a display panel displaying a plot of a
hemodynamic parameter over time and superimposed thereover an
indication of the level of consciousness in number format; and
[0065] FIG. 7 shows a flow diagram for restoring blood pressure
and/or blood flow in a patient following a decrease in blood flow
or pressure during anaesthetic induction
DETAILED DESCRIPTION OF EMBODIMENTS
[0066] An embodiment of the present invention will be described in
the following. FIG. 1 shows an overview of a monitor 100 of an
embodiment of the present invention. The monitor 100 comprises an
input port 110 to which a device providing an analogue pressure
waveform can be connected and through which the analogue pressure
waveform can be input into the monitor 100. An analogue to digital
converter 120 is provided for converting any analogue pressure
waveform received through the input port 110 into a digital signal.
The digital signal can be placed on the bus 130 for further
processing. The monitor 100 further comprises a second input port
140 to which a device providing a BIS signal can be connected and
through which the BIS signal can be input into the monitor 100. In
the present case the BIS signal is assumed to be a digital signal,
so that it can be used directly by the monitor 100 without prior
analogue to digital conversion. It will, however, be appreciated
that other arrangements, in which an analogue to digital converter
is used for converting an analogue signal indicative of a patient's
level of consciousness prior to supplying this signal to the bus
130, are also contemplated. The monitor 100 further comprises a
microprocessor 150, a RAM 160, which may act as buffer, permanent
storage means provided in the form of a hard drive 170 and some
input/output means 180. Examples of such input/output means are
monitors, printers and keyboards etc. Although not shown, the
monitor 100 may further comprise input means through which a signal
indicative of the heart rate of the patient may be received.
[0067] The results of a study conducted at Kings College Hospital,
London, UK are discussed in the following. The purpose of the study
was to quantify the changes occurring across anaesthetic induction
in arterial pressure, cardiac output and systemic vascular
resistance from their pre-induction baseline level in peripheral
vascular surgery patients. The correlation of these hemodynamic
changes with post induction preload responsiveness parameters and
the change in depth of anaesthesia was also explored.
[0068] Forty-six adult patients (36 male, 10 female) with ASA
grades between 2 or 4 (94% grade 3 to 4) undergoing complex
peripheral vascular surgery (mean duration 4.1 hours) with an
average age of 73 years (range 46-92) were studied. Anaesthetic
induction was with remifentanil and propofol target controlled
infusion (TCI). Changes of hemodynamic data from the pre-induction
baseline to immediately post intubation were recorded from analysis
of the peripheral artery pressure waveform using the LiDCO
hemodynamic monitor (LIDCO Ltd., UK). Changes of depth of
anaesthesia from the pre-induction baseline to immediately post
intubation were recorded from the patients' foreheads (BIS from
Covidien). One minute average changes in hemodynamic and BIS
results were compared.
[0069] The average fall in mean arterial pressure was -40%.+-.12%
(range -13% to -62%). This fall was predominantly driven by a
reduction in cardiac output fall of -33%.+-.14% (range: +15 to
-58%) and a lesser average reduction from baseline in systemic
vascular resistance of -6%.+-.18% (range: +31 to -36%). On average
the reduction in cardiac output contributed 82% of the pressure
fall and only increased in one out of the 46 patients. Systemic
vascular resistance in contrast fell in 28 out of the 46 patients
and was unchanged or rose in 18 out of the 46. The fall in cardiac
output reflected a 28% reduction in stroke volume (.+-.15%; range:
+10 to -63%) plus a much smaller reduction of -7% (.+-.13%; range:
34 to -37%) in the average heart rate.
[0070] The average stroke volume variation SVV% immediately post
induction and intubation was 17%. 16 patients (35%) were not fluid
responsive (with the stroke volume variation being less than 10%;
SVV%<10%). 20 patients (44%) were fluid responsive (with the
stroke volume variation being greater than or equal to 10%; SVV% a
10%). Ten patients suffered from a degree of heart rate variation
post intubation that precluded stroke volume based fluid
responsiveness evaluation. The reductions in cardiac output and
stroke volume fluid responsive patients was significantly greater
than in non-responsive subjects (t test SPSS, cardiac output
reduction of -36% for fluid responsive patients, compared to a
reduction in cardiac output of -24% for fluid non-responsive
patients, P<0.001 and a reduction in stroke volume of -31% for
fluid responsive patients compared to a reduction in stroke volume
of -17% for fluid non responsive patients, P<0.001).
[0071] The average fall in BIS was 58% .+-.11% (range 91.3 to
39.5). For each patient there was a good correlation/linear
relationship (Pearson correlation coefficient) between the
responding hemodynamic parameter(s) and the absolute BIS value and
the percentage change in BIS value. Recorded data for one of the
patients are illustrated in FIG. 2. The correlation between BIS and
mean arterial pressure, stroke volume and systemic vascular
resistance respectively is illustrated in FIG. 3 the data
illustrated in FIG. 2. The average reduction, when compared to
pre-induction levels, in hemodynamic parameter per unit change in
BIS was: Cardiac output 47 ml/min (range 0.11 to -0.01 l/min), mean
arterial pressure 0.75 mmHg (range 1.74 to 0.14 mmHg), heart rate
0.108 beats/min (range 0.76 to -0.41 bpm), stroke volume 0.461 ml
(range 1.5 to -0.16 ml) and systemic vascular resistance 1.9 dynes
s cm.sup.-5 (range 17.69 to -9.82 dynes s cm.sup.-5).
[0072] The observed correlation between BIS and the hemodynamic
parameter(s) means that brain EEG activity level monitoring with
BIS, and possibly other EEG monitors/EEG monitors, mirror the time
course and are directly proportional to the strength of the effects
of the anaesthetic agent(s) on blood pressure/hemodynamics.
Excessively low levels of brain activity, as a consequence of too
much anaesthesia, are consequently potentially deleterious to the
patient as they lower blood pressure and blood flow/oxygen delivery
further than is necessary for the purpose of anaesthesia.
[0073] The study has indicated that the fall in blood pressure
during induction of anaesthesia is partly driven by the patient's
fluid status, in particular a reduction in blood flow, and, to a
lesser degree, by the patient's level of consciousness/depth of
anaesthesia. This reduction in blood flow is mostly due to a
reduction in left ventricular stroke volume. Changes in the
systemic vascular resistance play a lesser role. The falls seen in
cardiac output and stroke volume are significantly worse in the
presence of preload responsiveness than in patients that are not
fluid responsive. Changes in depth of anaesthesia/level of
consciousness, as measured by BIS, correlate well with these
hemodynamic changes. Although the slope of a fitted linearly
function indicating the relationship between BIS and hemodynamic
parameters varies between patients it is clear from the study that
allowing higher BIS scores will in general be associated with
improvements to both blood flow and pressure. Simultaneous
monitoring of blood flow, SVR, blood pressure and fluid
responsiveness while maintaining anaesthesia depth to a target
should allow finer discrimination and more efficient control of the
hemodynamic changes seen consequent to induction.
[0074] FIG. 4 shows an example of a display 200 according to one
embodiment. The display is a flat panel display comprising two
areas 220 and 230. The processor 150 causes the display to display
hemodynamic parameters in area 220 and an indication of the level
of consciousness, in this case bispectral index, in area 230. Area
220 in turn is divided into an upper, middle and lower panel. The
upper panel comprises a display area 240. In this display area 240
the received arterial blood pressure signal is plotted over time,
giving rise to the wide band displayed in this area of FIG. 4. Also
plotted over time is the patient's mean arterial blood pressure and
the patient's heart rate. Both the trace for mean arterial blood
pressure and for heart rate are, in this example, superimposed over
the band created by the display of the blood pressure signal. These
values are displayed over a long time period in display area 240,
in this example over 10 minutes, to allow clinicians to observe, at
a single glance and without having to manipulate display
parameters, any trends or long term changes in the displayed
parameters. The time period chosen for the display area 240 can be
different from the 10 minute time scale chosen in this example, as
long as an appreciation of long term changes and trends is
possible. The monitoring device may moreover allow a user to set
the time scale for this display window to meet the user's
requirements and/or may facilitate automatic scaling of the time
scale to the duration of the display.
[0075] The processor is further arranged to provide event markers
260 in long term display area 240 to indicate the points in time at
which interventions have been conducted. The processor may allow a
user to input a description of the nature of the event. The
numbering of the event markers 260 in FIG. 4 allows easy
identification of the nature of such an event via a list of event
description maintained by the monitoring device.
[0076] The upper display panel also comprises a shorter term
display area 250. The parameters displayed in display area 250 are
the same as those displayed in display area 240. However, the time
scale chosen for display area 250 is shorter (in this case 2
minutes) than the time scale chosen for display area 240. The
amount of detail (resolution) displayed in display area 250 is
higher than that displayed in display area 240. The combination of
display areas 240 and 250 thus allows observing long term changes
in the displayed parameters (though display area 240) and shorter
term changes/acute changes (though display area 250). The mean
arterial blood pressure as well as the systolic and diastolic blood
pressures are moreover displayed in number format in area 270. The
heart is moreover displayed in number format in area 280.
[0077] The middle panel of area 220 also comprises a long term
display area 290 and a short term display area 300 similar to the
long and short term display areas 240 and 250 of the upper panel of
the area 220. The long and short term display areas 290 and 300,
however, plot cardiac output over time. The cardiac output is
moreover displayed in number format in area 310 alongside an
indication of stroke volume in number format in area 320.
[0078] The lower panel of display area 200 is an event response
display 330 plotting a change of a hemodynamic parameter, in this
case stroke volume, over time since the occurrence or input of an
event. This change is in this example plotted as a percentage
change of the stroke volume at the time of the event. A current
value of this percentage change is also shown in number format in
area 340.
[0079] The processor causes an indication of the level of
consciousness, in this case bispectral index, of the patient to be
displayed in display area 350 of area 230. The level of
consciousness is plotted over time. A band 360 indicates the range
of bispectral index values (from 40 to 60) that is normally
clinically accepted as preventing awareness/post surgical recall,
while being sufficiently high to minimise side effects of the
anaesthetic process. Also provided is a display 370 of the current
bispectral index value in number format.
[0080] It will be appreciated that, although in FIG. 4 the display
350 is not provided in a time synchronised fashion with displays
240 and 290 (which are time synchronised to each other) or with
displays 250 and 300 (which are also time synchronised to each
other), time synchronisation of display 350 to one or more of
displays 240, 250, 290 and 300 can also be provided. Additionally
or alternatively the event markers 260 shown in FIG. 4 may also be
provided in the display area 350, so that clinicians can, at one
glance and without having to manipulate the display of the
monitoring device, link a change evident from the display areas 240
and/or 290 with a change in the level of consciousness, as
displayed in area 350.
[0081] FIG. 5 shows a further display panel 400. This further
display panel 400 may be displayed alongside the display panels
shown in FIG. 4, for example immediately above it or below it, or
besides the lower display panel of FIG. 4 that comprises display
area 330. Alternatively the display panel 400 may replace one of
the upper, middle or lower display panels shown in FIG. 4, for
example. The display panel 400 comprises a display area 410 in
which a maximum stroke volume variation over a predetermined period
of time is plotted over time. The predetermined period of time can
be a respiratory cycle, so that display area 410 displays changes
in stroke volume over the respiratory cycle. Also displayed in area
410 is a boundary zone 420 for the stroke volume variation. The
boundary zone defines the area of 10% variation in stroke volume.
Variations in the stroke volume going beyond this area may be
considered by the clinician as indicating that the patient is
hypovolemic. The time scale of the display area 410 is such that
long term changes in stroke volume variation can be observed. It
will be appreciated that, although not shown in FIG. 5, event
markers similar or equivalent to event markers 260 shown in FIG. 4
may also be displayed. Also provided is a shorter term plot 430 of
stroke volume (rather than stroke volume variation) over time. The
time scale of plot 430 has been chosen such that variations in
stroke volume over a small number of respiratory cycles can be
observed. A band 440 indicating 10% variation of the actual stroke
volume is also displayed to enable to clinician to form a view on
whether or not the patient may be or become hypovolemic. The
current stroke volume variation value is also displayed in number
format in area 450 alongside area 430.
[0082] As mentioned above, it may further be useful for the
clinician if an indication of changes that can likely be gained in
blood pressure or blood flow with a change in another parameter was
available. FIG. 3 provides such an indication. It shows, for
example, that mean arterial blood pressure (MAP) and stroke volume
(SV) are directly proportional to the bispectral index. FIG. 3 thus
intuitively shows that in situations where a patient's level of
consciousness has been lowered below a level needed to prevent
awareness/post surgical recall, a reduction in the amount of
anaesthetic or sedative administered to the patient can bring about
an improvement in mean arterial blood pressure and/or stroke
volume. FIG. 3 also indicates that a change in the level of
consciousness of the patient is unlikely to bring about a change in
systemic vascular resistance. It will be appreciated that
indications of this nature can be clinically useful, although a
decision on how blood pressure and flow should or could be raised
to a desired level lies of course entirely with the clinician. It
is thus envisaged that one or more of the fitted curves shown in
FIG. 3 may be displayed on the display of the monitoring device.
The display of fitted curves other than those shown in FIG. 3 is
also envisaged. Additionally or alternatively the slope of the
fitted curve(s) can be displayed in number format (expressed for
example in mmHg/BIS unit for MAP or in ml/BIS unit for stroke
volume) to give clinicians an indication of a likely change brought
about by an induced change in the level of consciousness of the
patient or simulated patients.
[0083] It will be appreciated that the present invention is not
limited to the embodiments described above. It is moreover
envisaged that different ways of displaying a level of
consciousness and the patient's hemodynamic parameters may be used
during different stages of anaesthetic induction. In the induction
phase, for example, up until the intubation of the patient, the
processor may cause the display to display blood pressure, the
drivers of changes in blood pressure, cardiac output and systemic
vascular resistance and the level of consciousness of the patient.
These displays can be superimposed over each other to provide a
compact display. Alternatively, these displays can be separately
provided in three panels so allow easy analysis of the displayed
data. Following intubation the processor may cause the display to
change (for example after user input of an event indicating the
completion of intubation), for example to the display shown in FIG.
4, to allow an easy and quick analysis of the changes in the
hemodynamic parameters of the patient alongside the changes in the
level of consciousness. It is particularly envisaged that a display
of this nature and for this purpose should comprise a plot of blood
pressure, cardiac output, means arterial pressure or systolic
pressure and the level of consciousness over time.
[0084] Following an analysis of the reasons for a drop in arterial
blood pressure during anaesthetic induction, an anaesthetist will
likely be interested in addressing any identified reasons for such
a drop. The processor can be arranged to aid the anaesthetist's
attempts to reverse this trend by displaying those hemodynamic
parameter useful for observing the patient's reactions to any steps
taken by the anaesthetist. As discussed above, a plot of a
variation of stroke volume over time or of stroke volume variation
over time (as, for example, shown in FIG. 5) can be useful for
identifying a hypovolemic state of the patient. In one embodiment a
plots of blood pressure, heart rate, cardiac output and systemic
vascular resistance is further provided alongside a plot of the
level of consciousness of the patient over time.
[0085] The description of embodiments above has focussed on the
display of the level of consciousness in the form of a graph. As
also discussed above, this is not essential, however, and FIG. 6
shows an alternative or additional way of displaying the level of
consciousness. FIG. 6 shows a display panel 500 displaying long and
a short term displays of cardiac output. Superimposed over the long
term display of the cardiac output are the values of the level of
consciousness of the patient at the time point at which the value
is displayed. As suggested in FIG. 6, the height at which the value
indicating the level of consciousness if displayed above the bottom
edge of the display panel can also be indicative of the level of
consciousness the patient had at the time, although positioning the
numbers in this fashion is optional. It will of course be
appreciated that, while FIG. 6 combines the display of cardiac
output with the display of numbers representing the level of
consciousness of the patient, such a number display can be paired
with one or more displays of other hemodynamic parameters, for ,
example with a display of stroke volume, stroke volume variation
and mean or systolic blood pressure.
[0086] FIG. 7 shows a flow chart of a method 700 of increasing a
patient's blood pressure and/or blood flow following a change in
blood pressure and/or flow during anaesthetic induction. Initially
the level of consciousness is determined in a step 710. If the
level of consciousness is not within a desired range of values,
then the level of consciousness is adjusted in step 720 by altering
the amount of anaesthetic or sedative administered.
[0087] It is then determined in step 730 if the mean arterial blood
pressure, the systolic blood pressure, the cardiac output and/or
the stroke volume is below a desired threshold value. In the
unlikely event that this is not the case the method is terminated.
Should the desired threshold values not be reached by one or more
of these parameters, then it is determined if the patient is
hypovolemic in step 740. If the patient is hypovolemic, then a
fluid challenge of, for example, 200 ml is administered in step 750
and the patients fluid status is again checked in step 740. The
administering of fluid challenges can be repeated a number of times
if it is repeatedly determined in step 740 that the patient is
hypovolemic.
[0088] If it is determined in step 740 that the patient is not
hypovolemic, then it is again determined in step 760 if the mean
arterial blood pressure, the systolic blood pressure, the cardiac
output and/or the stroke volume is below the desired threshold
value.
[0089] Should this still be the case, then a staged approach of
administering drugs that may be suitable for increasing blood flow
and/or blood pressure is used in step 770 to identify which
particular drug is suitable to increase blood pressure/blood flow
in the particular patient. Drugs having a more time limited effect
may be administered first in this staged approach and their effect
on blood flow and blood pressure is observed on the monitoring
device. Drugs having a more lasting effect may be administered
later in this staged approach, if the earlier administered drugs
have not shown to have the desired effect, followed again by an
observation of their effects.
[0090] It will be appreciated that the above description of the
present invention is made by way of example only to illustrate the
present invention. The person skilled in the art will appreciate
that the present invention is not limited by the examples provided
above.
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