Title: Method for continuous monitoring of patients to detect the potential onset of sepsis
Abstract: A method of screening for possible onset of sepsis in a patient includes providing the patient with a transducer that automatically and periodically measures a first physiological parameter of the patient and transmits a first signal that is encoded with the measured parameter value, and receiving the first signal and automatically comparing the measured parameter value with at least one alarm limit. The first physiological parameter is body temperature, heart rate, respiration rate or a clinical indicator of sepsis. A conditional warning signal is asserted in the event that the measured parameter value bears a predetermined relationship to said alarm limit and an alarm signal is issued in the event that a physiological condition other than the condition that gave rise to the conditional warning signal is indicative of onset of sepsis.
Patent Number: 7,022,070 Issued on 04/04/2006 to Ebner, et al.
| Inventors:
|
Ebner; Dennis M. (Sisters, OR);
McKenzie; Jack E. (Bend, OR)
|
| Assignee:
|
Mini-Mitter Co., Inc. (Bend, OR)
|
| Appl. No.:
|
393455 |
| Filed:
|
March 19, 2003 |
| Current U.S. Class: |
600/301; 600/500; 600/508; 600/529; 600/549 |
| Current Intern'l Class: |
A61B 5/00 (20060101) |
| Field of Search: |
600/300,301,500-503,529,549
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
Spandorfer et al. "Sugar and Spice and Everything Nice", Pediatric Annals. Oct.
2001; 30, 10: Health & Medical Complete, pp. 603-606.
Beal et al. "Multiple organ failure syndrome in the 1990s", JAMA. Chicago: Jan.
19, 1994, v. 271, iss. 3, pp. 226-234.
Creechan et al. "Cooling by Convection Vs. Cooling by Conduction for Treatment
of Fever in Critically III Adults", American Journal of Critical Care; Jan. 2001;
vol. 10, No. 1, pp. 52-59.
Bone et al. "Definitions for Sepsis and organ failure and guidelines for the
use of innovative therapies in sepsis", Chest. Jun. 1992.
"Urosepsis, Septicemia, Urinary Tract Infection (UTI) Audit Tool" NMMRA, Feb.
27, 2002, p. 2.
Finkelstein et al. "Fever in Pediatric Primary Care: Occurrence, Management,
and Outcomes", Pediatrics. Jan. 2000; vol. 105, No. 1, pp. 260-266.
Sands et al. "Epidemiology of Sepsis Syndrome in 8 Academic Medical Centers"
JAMA. Jul. 16, 1997; vol. 278, No. 3; pp. 234-240.
Rangel-Frausto et al. "The Natural History of Systemic Inflammatory REsponse
Syndrome (SIRS)" JAMA. Jan. 11, 1995; Col. 273, No. 2; pp. 117-123.
Bauer et al. "Effect of Sepsis Syndrome on Neonatal Oxygen Consumption and Energy
Expenditure," Pediatrics Dec. 2002. vol. 11, No. 6. pp. 1-4.
|
Primary Examiner: Nasser; Robert L.
Assistant Examiner: Mallari; Patricia
Attorney, Agent or Firm: Smith-HIll; John, Smith-Hill and Bedell
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims benefit of U.S. Provisional Application No. 60/367,076
filed Mar. 22, 2002 and U.S. Provisional Application No. 60/394,340 filed Jul.
3, 2002, the entire disclosure of each of which is hereby incorporated by reference
herein for all purposes.
Claims
The invention claimed is:
1. A method of screening for possible onset of sepsis in a patient, comprising:
(a) providing the patient with a first transducer that automatically measures
core body temperature and intermittently transmits a first signal that is encoded
with the measured value of core body temperature,
(b) providing the patient with at least one transducer that automatically measures
heart rate and respiration rate and intermittently transmits at least one signal
that is encoded with the measured values of heart rate and respiration rate,
(c) receiving the signals transmitted by the transducers and automatically comparing
the measured values of core body temperature, heart rate and respiration rate with
respective alarm limits, and
(d) issuing an alarm signal in the event that at least one of the measured values
bears a predetermined relationship to its alarm limit and the patient also exhibits
at least one of redness around an infection site, swelling and facial pallor.
2. A method according to claim 1, wherein said first transducer is implemented
in an ingestible thermometer.
3. A method according to claim 1, wherein step (b) comprises providing the patient
with first and second transducers that automatically measure heart rate and respiration
rate respectively and intermittently transmit second and third signals that are
encoded with the measured values of heart rate and respiration rate.
4. A method according to claim 3, wherein said second and third transducers are
implemented in a removable skin patch.
5. A method according to claim 1, wherein step (b) comprises providing the patient
with a transducer that acquires an ECG signal, automatically measures heart rate
and respiration rate based on characteristics of the ECG signal, and transmits
at least one signal that is encoded with the measured values of heart rate and
respiration rate.
6. A method according to claim 1, further comprising:
(a) in the event that the alarm signal is issued, testing the patient for sepsis.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for continuous monitoring of patients to
detect the potential onset of sepsis.
Sepsis is a medical condition in which bacteria invade the body causing a
serious infection. Large and increasing numbers of microorganisms overwhelm the
body's defense systems and actively multiply in the bloodstream. Sepsis is associated
with a large stress on the body, such as trauma.
Over 684,000 cases of sepsis were reported in the United States in 1998. The
mortality rate for these cases was 17.4%. Overall, sepsis is the 11th leading cause
of death in the U.S. and the annual cost of providing care for this condition is
approximately $15 billion.
Sepsis is almost always accompanied by an increase or decrease in body core
temperature as well as elevation in pulse and respiration rates.
Current hospital care protocols for detecting onset of sepsis require periodic
body temperature, pulse rate, and respiration rate monitoring, and patient observation.
A typical sepsis screening criterion used by healthcare providers is as follows:
- a. Body core temperature greater than 38.3° C. (about 101°
F.) or less than 35.6° C. (about 96° F.).
- b. Heart rate greater than 90 beats per minute.
- c. Respiration rate greater than 20 respirations per minute.
- d. Clinical evidence of infection, such as redness around an infection
site, swelling, or facial pallor.
The presence of any two of these four factors is considered to be an indication
of the potential onset of sepsis, rendering further patient evaluation, including
blood cultures and chest x-rays, desirable. If the further evaluation confirms
the diagnosis of sepsis, the accepted clinical treatment is the administration
of substantial doses of intravenous antibiotics.
Early detection of sepsis and appropriate administration of antibiotics can
greatly reduce the mortality rate of this disease.
For a patient who has not been admitted to a critical care unit or intensive
care unit, the intervals at which body temperature, heart rate and respiration
rate are measured during hospitalization can be quite long and quite variable and
may depend on circumstances other than the current condition of the patient, such
as the workload of nurses and other healthcare professionals.
It can be appreciated that more frequent body temperature, heart rate and respiration
rate monitoring could be helpful in detecting the possible onset of sepsis so that
a rapid diagnosis and immediate care can be provided to thwart this disease from
rapidly overwhelming the patient's immune system.
U.S. patent application Ser. No. 10/017,098 discloses a digital sensor for a
miniature medical thermometer and body temperature monitor. This digital sensor
can be implemented in a pill that can be ingested for measuring body core temperature,
in a small skin patch for measuring skin temperature, or in a capsule that can
be placed in a body orifice, such as the ear canal.
U.S. patent application Ser. No. 10/071,534 discloses a skin patch including
a telesensor for emitting a signal that represents a physiological parameter sensed
by the telesensor. The physiological parameters that can be sensed by an appropriate
telesensor include body temperature and ECG voltage. It is known that heart rate
and respiration rate can be derived from the ECG voltage waveform.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention there is provided a method
of screening for possible onset of sepsis in a patient, comprising (a) providing
the patient with a transducer that automatically and periodically measures a first
physiological parameter of the patient and transmits a first signal that is encoded
with the measured parameter value, (b) receiving the first signal and automatically
comparing the measured parameter value with at least one alarm limit, (c) asserting
a conditional warning signal in the event that the measured parameter value bears
a predetermined relationship to said alarm limit, and (d) issuing an alarm signal
in the event that another physiological condition is indicative of onset of sepsis,
and wherein said first physiological parameter is body temperature, heart rate,
respiration rate or a clinical indicator of sepsis.
In accordance with a second aspect of the invention there is provided a method
of screening for possible onset of sepsis in a patient, comprising (a) providing
the patient with a first transducer that automatically and periodically measures
the patient's core temperature and transmits a first signal that is encoded with
the measured core temperature value, (b) providing the patient with a second transducer
that automatically and periodically measures a reference temperature of the patient
and transmits a second signal that is encoded with the measured reference temperature
value, (c) receiving the first and second signals and automatically comparing the
measured core temperature value with the measured reference temperature value,
(d) issuing a warning signal in the event that the measured temperature value bears
a predetermined relationship to the measured reference temperature value, and (e)
testing the patient for onset of sepsis.
In accordance with a third aspect of the invention there is provided a method
of screening for possible onset of sepsis in a patient, comprising (a) providing
the patient with a transducer that automatically measures the patient's interbeat
interval, (b) calculating the patient's heart rate variability, (c) issuing a warning
signal in the event that the calculated value of heart rate variability bears a
predetermined relationship to a reference value, and (d) testing the patient for
onset of sepsis.
In accordance with a fourth aspect of the invention there is provided a method
of screening and testing for sepsis in a patient, comprising providing the patient
with an automatic thermometer that periodically measures the patient's body temperature
and transmits a temperature signal that is encoded with the measured temperature
value, receiving the temperature signal and automatically comparing the measured
temperature value with at least one alarm limit, asserting a warning signal in
the event that the measured temperature value bears a predetermined relationship
to said alarm limit, determining whether another physiological condition is indicative
of onset of sepsis, and, if so, testing the patient for sepsis.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, and to show how the same may be
carried into effect, reference will now be made, by way of example, to the accompanying
drawings, in which:
FIG. 1 is a flow chart illustrating the principal steps of a first method embodying
the present invention,
FIG. 2 is a flow chart illustrating the principal steps of a second method embodying
the present invention, and
FIG. 3 is a flow chart illustrating the principal steps of a third method embodying
the present invention.
DETAILED DESCRIPTION
In the first method embodying the invention, a patient who is admitted to the
hospital is provided with a body temperature sensor, a heart rate sensor and a
respiration rate sensor (FIG. 1, step
10).
The body temperature sensor may be the sensor described in U.S. patent application
Ser. No. 10/017,098. Preferably the body temperature sensor is implemented in a
pill to be ingested by the patient but it may alternatively be implemented in another
form, such as a skin patch. In the event that the body temperature sensor is implemented
in a pill, the sensor is activated just before it is given to the patient and the
patient then swallows the pill. The sensor periodically emits a signal representative
of the patient's core temperature.
The heart rate sensor and the respiration rate sensor may be implemented in a
skin patch of the general type described in U.S. patent application Ser. No. 10/071,534
but in which the telesensor is configured to acquire an ECG voltage waveform and
includes a processor that is programmed to compute a heart rate value and a respiration
rate value from the ECG voltage waveform. The telesensor periodically emits a signal
that is encoded with the current heart rate and the current respiration rate.
Alternatively, the heart rate sensor may be implemented in a first
skin patch including a telesensor that is configured to provide an indication of
heart rate and the respiration rate sensor may be implemented in a second skin
patch including a telesensor that is configured to provide an indication of respiration
rate. The telesensors of the first and second skin patches may each acquire an
ECG voltage and calculate the heart rate and respiration rate respectively from
the ECG voltage waveform, but alternatively either telesensor may rely on a physiological
parameter other than ECG voltage to calculate heart rate or respiration rate, as
the case may be.
The patient is also provided with a portable recorder or monitor that accompanies
the patient during the patient's hospital stay and includes a receiver unit for
receiving the signals emitted by the sensors. A suitable receiver unit for calculating
the patient's core temperature from the signal emitted by the ingestible pill is
disclosed in U.S. patent application Ser. No. 10/017,098. The recorder monitors
the calculated core temperature (step
12) and compares the calculated core
temperature with predetermined alarm limits, e.g. a high alarm limit of 38.3°
C. (about 101° F.) and a low alarm limit of 35.6° C. (about 96°
F.), and asserts a conditional warning signal in the event that the calculated
core temperature deviates from the range defined by the alarm limits (steps
14
and
16).
The receiver unit also receives the heart rate signal and the respiration rate
signal from the skin patch and compares the heart rate and the respiration rate
with predetermined high alarm limits, such as 90 heartbeats per minute and 20 respirations
per minute, and asserts a conditional warning signal in the event that either rate
exceeds the appropriate high alarm limit (step
18).
The recorder may be provided with an event marker button that may be pressed
by a healthcare professional observing the patient in order to record the fact
that the patient is exhibiting clinical evidence of infection. When the event marker
button is pressed, a circuit in the recorder asserts a conditional warning signal.
If two of the four potential conditional warning signals are asserted concurrently,
the recorder emits an alarm signal (step
19), which may be audible and/or
visible, in order to alert a responsible healthcare professional of the possible
onset of sepsis in the patient. The recorder may also transmit an alarm signal
by radio to a nurses' station.
Upon receiving the alarm signal, a nurse or other healthcare professional initiates
action, which may be conventional tests, to determine whether there has in fact
been an onset of sepsis in the patient (step
20). If sepsis is diagnosed
(step
22), treatment is initiated (step
24); otherwise treatment
for sepsis is not initiated. In the event that sepsis is not diagnosed, one or
more of the alarm limits may be adjusted in order to avoid a further false alarm.
It will be appreciated that although FIG. 1 has been described as if the warning
signal asserted in response to the event marker button being pressed were a secondary
signal that confirms a conditional warning signal that was previously provided
by the temperature sensor, the heart rate sensor or the respiration rate sensor,
the warning signal asserted in response to the event marker button being pressed
may be the conditional warning signal that is confirmed by a secondary signal provided
by one of the electronic sensors.
The splanchnic circulation (blood flow to the small intestine) transfers nutrients
from the intestine to the blood and facilitates the transport of the nutrient rich
blood to the liver via the hepatic-portal system for the processing of the metabolic
nutrients. In addition, the splanchnic circulation provides oxygen and heat to
the tissue to facilitate the metabolic process. The splanchnic circulation is about
one third of the circulating blood volume of the circulatory system. The splanchnic
circulation has a very finely controlled vasoconstriction mechanism that is regulated
by the sympathetic nervous system and allows a part of this vast volume of blood
to be diverted to other areas of the body during physiological stress.
It is believed that a mechanism by which physiological stress may lead to sepsis
is that the vasoconstriction of the splanchnic circulation in response to the stress
results in a reduced oxygen delivery to the gut which in turn causes ischemia and
death of the cellular membrane of the epithelium, allowing the enteric bacteria
to enter the bloodstream.
Based on the foregoing analysis, it appears that a reduction in the splanchnic
circulation may be predictive of onset of sepsis. Further, since the delivery of
blood to the intestinal tissue regulates intestinal temperature, a change in splanchnic
temperature relative to other large tissue masses, primarily muscle, will provide
an indirect measure of blood flow to the gut.
In a second method embodying the present invention, a patient entering the hospital
is provided with a body core temperature sensor in the form of a pill as described
with reference to FIG. 1 (FIG. 2, step
110), a skin temperature patch that
is applied to a large tissue mass, such as a large muscle mass or the chest (step
112), and a portable recorder or monitor.
The body core temperature sensor emits a signal that is encoded with the splanchnic
temperature and the skin patch emits a signal that is encoded with a temperature
that is not directly affected by splanchnic vasoconstriction and vasodilation and
serves as a reference temperature for comparison with the splanchnic temperature.
The recorder periodically calculates the difference between the splanchnic temperature
and the reference temperature (step
114) and emits an alarm signal in the
event that the splanchnic temperature decreases below the reference temperature
by an amount that exceeds a predetermined alarm limit (steps
116 and
118).
In response to the alarm signal, a healthcare professional initiates action, which
may include conventional tests (step
120), to determine whether sepsis has
in fact occurred. If sepsis is diagnosed, treatment is initiated (step
122);
otherwise treatment for sepsis is not initiated.
Of course, the signal that is initiated in step
118 may be used as a conditional
warning, as described with reference to FIG. 1, such that an alarm signal is not
issued unless the warning signal is qualified by another warning condition. It
will be understood that in this case the physiological parameter that is monitored
in step
12, or that gives rise to the second warning (step
18), is
the difference between the splanchnic temperature and the reference temperature.
The pacemaker cells in the right atria of the heart determine the intrinsic rate
of the heart. However, the heart can be accelerated by the sympathetic nervous
system, which releases the neurotransmitter norepinephrine, and the heart can be
slowed by the parasympathetic nervous system and its neurotransmitter acetylcholine.
Both the sympathetic and parasympathetic nervous system release neurotransmitters
on a beat to beat basis to finely regulate heart rate, based on feedback from receptors
and from the brain through the central nervous system.
The interbeat interval or IBI (the interval between consecutive beats of the
heart) can vary quite widely. An accepted measure of the variability of the IBI
is known as the heart rate variability or HRV and is determined by measuring multiple
values of the IBI over a test interval and applying a mathematical operation to
the IBI values.
In a normal resting individual, the HRV is quite large. As the heart rate increases,
for example due to activity of the sympathetic nervous system, the HRV decreases.
Since the sympathetic nervous system controls both the heart rate and the vasoconstriction
of the splanchnic circulation, it appears likely that a reduction in the HRV may
be predictive of a decrease in splanchnic circulation.
In a third method embodying the invention, a patient entering the hospital is
provided with a skin patch including a telesensor that is configured to acquire
an ECG voltage waveform and includes a processor that is programmed to compute
the patient's HRV (FIG. 3, step
210). The telesensor periodically emits
a signal that is encoded with the current HRV value.
The patient is also provided with a portable recorder or monitor that accompanies
the patient during the patient's hospital stay and includes a receiver unit for
receiving the signal emitted by the telesensor. The recorder calculates change
in HRV, and may calculate change in HRV relative to other physiological parameters.
If the change in HRV exceeds a predetermined alarm limit, the recorder emits an
alarm signal and the method proceeds as described with reference to FIG. 2.
Physiological parameters that might be useful input variables for a
sepsis alert algorithm that processes the HRV values include core body temperature,
heart rate and respiration rate, all of which can be acquired using the skin patch
and/or pill referred to in connection with FIGS. 1 and 2.
The alarm signal that is emitted in step
218 may be used as a conditional
warning, such that an alarm signal is not issued unless the warning signal is qualified
by another warning condition. It will be understood that in this case the physiological
parameter that is monitored in step
12 (FIG. 1), or that gives rise to the
second warning (step
18), is the change in HRV.
Although the foregoing description of FIG. 2 refers to use of a pill to
detect body core temperature and a skin patch to detect a reference temperature
that is not directly affected by splanchnic vasoconstriction and vasodilation,
it will be understood that the broad idea of using variation in splanchnic temperature
as a predictor of potential onset of sepsis is not restricted to the particular
mechanisms that are used to detect the body core temperature and the reference
temperature. Similarly, although FIG. 3 refers to use of a skin patch including
a telesensor that is configured to acquire an ECG voltage waveform, it will be
understood that the broad idea of using HRV as a predictor of potential onset of
sepsis is not restricted to the particular mechanism that is used to measure IBI.
The methods described above of monitoring vital signs for early warning of the
onset of sepsis are ambulatory and would not restrict the patient to any particular
healthcare environment (e.g. CCU). The patient would be free to move about the
hospital environment or indeed, could be monitored at home, thereby offering a
continued protective benefit for the early detection of sepsis, post-hospital environment.
Implementation of this method will have the following benefits:
- 1. Reduction in mortality rate of sepsis. This condition would be detected
earlier, causing healthcare intervention to occur faster, thereby stopping the
disease's progression toward possible death of the patient.
- 2. Early detection of sepsis, along with administration of antibiotics,
will greatly enhance the patient's recovery pace at the hospital, speeding his
discharge from the hospital, thereby lowering the overall healthcare cost.
- 3. The methods could be deployed to the patient's home thereby offering
a continued protective benefit for the early detection of sepsis, post-hospital environment.
- 4. Continuous patient vital signs monitoring with alarm signaling will
reduce the need for periodic vital signs monitoring conducted manually by a nurse
and thereby decrease the nurse to patient contact time. This would represent a
productivity improvement for the nurse and hospital.
It will be appreciated that the invention is not restricted to the particular
embodiments that have been described, and that variations may be made therein without
departing from the scope of the invention as defined in the appended claims and
equivalents thereof. Unless the context indicates otherwise, a reference in a claim
to the number of instances of an element, be it a reference to one instance or
more than one instance, requires at least the stated number of instances of the
element but is not intended to exclude from the scope of the claim a structure
or method having more instances of that element than stated.
*
