US20150087936A1 - Physiological parameter system - Google Patents

Abstract

A physiological parameter system has one or more parameter inputs responsive to one or more physiological sensors. The physiological parameter system may also have quality indicators relating to confidence in the parameter inputs. A processor is adapted to combine the parameter inputs, quality indicators and predetermined limits for the parameters inputs and quality indicators so as to generate alarm outputs or control outputs or both.

Description

PRIORITY CLAIM TO RELATED PROVISIONAL APPLICATIONS
• The present application is a continuation of U.S. patent application Ser. No. 11/963,640, filed Dec. 21, 2007, entitled “Physiological Parameter System,” which claims priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 60/876,749, filed Dec. 22, 2006, entitled “Physiological Parameter System,” which is incorporated herein by reference.
FIELD OF THE DISCLOSURE
• The present disclosure relates to a sensor for measuring physiological parameters and, in particular, relates to using measured physiological parameters to generate an indicator.
BACKGROUND
• Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person's oxygen supply. Early detection of a low blood oxygen level is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. A typical pulse oximetry system utilizes a sensor applied to a patient's finger. The sensor has an emitter configured with both red and infrared LEDs that project light through the finger to a detector so as to determine the ratio of oxygenated and deoxygenated hemoglobin light absorption. In particular, the detector generates first and second intensity signals responsive to the red and IR wavelengths emitted by the LEDs after absorption by constituents of pulsatile blood flowing within a fleshy medium, such as a finger tip. A pulse oximetry sensor is described in U.S. Pat. No. 6,088,607 titled Low Noise Optical Probe, which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.
• Capnography comprises the continuous analysis and recording of carbon dioxide concentrations in the respiratory gases of patients. The device used to measure the CO₂concentrations is referred to as a capnometer. CO₂monitoring can be performed on both intubated and non-intubated patients. With non-intubated patients, a nasal cannula is used. Capnography helps to identify situations that can lead to hypoxia if uncorrected. Moreover, it also helps in the swift differential diagnosis of hypoxia before hypoxia can lead to irreversible brain damage. Pulse oximetry is a direct monitor of the oxygenation status of a patient. Capnography, on the other hand, is an indirect monitor that helps in the differential diagnosis of hypoxia so as to enable remedial measures to be taken expeditiously before hypoxia results in an irreversible brain damage.
• Early detection of low blood oxygen is critical in a wide variety of medical applications. For example, when a patient receives an insufficient supply of oxygen in critical care and surgical applications, brain damage and death can result in just a matter of minutes. Because of this danger, the medical industry developed pulse oximetry, a noninvasive procedure for measuring the oxygen saturation of the blood. A pulse oximeter interprets signals from a sensor attached to a patient in order to determine that patient's blood oxygen saturation.
• A conventional pulse oximetry sensor has a red emitter, an infrared emitter, and a photodiode detector. The sensor is typically attached to a patient's finger, earlobe, or foot. For a finger, the sensor is configured so that the emitters project light from one side of the finger, through the outer tissue of the finger, and into the blood vessels and capillaries contained inside. The photodiode is positioned at the opposite side of the finger to detect the emitted light as it emerges from the outer tissues of the finger. The photodiode generates a signal based on the emitted light and relays that signal to the pulse oximeter. The pulse oximeter determines blood oxygen saturation by computing the differential absorption by the arterial blood of the two wavelengths (red and infrared) emitted by the sensor.
SUMMARY
• Multiple physiological parameters, combined, provide a more powerful patient condition assessment tool than when any physiological parameter is used by itself. For example, a combination of parameters can provide greater confidence if an alarm condition is occurring. More importantly, such a combination can be used to give an early warning of a slowly deteriorating patient condition as compared to any single parameter threshold, which may not indicate such a condition for many minutes. Conditions such as hypovolemia, hypotension, and airway obstruction may develop slowly over time. A physiological parameter system that combines multiple parameters so as to provide an early warning could have a major effect on the morbidity and mortality outcome in such cases. Parameters can include ECG, EKG, blood pressure, temperature, SpO₂, pulse rate, HbCO, HbMet, Hbt, SpaO2, HbO2, Hb, blood glucose, water, the presence or absence of therapeutic drugs (aspirin, dapson, nitrates, or the like) or abusive drugs (methamphetamine, alcohol, or the like), concentrations of carbon dioxide (“CO2”), oxygen (“O”), ph levels, bilirubin, perfusion quality, signal quality, albumin, cyanmethemoglobin, and sulfhemoglobin (“HbSulf”) respiratory rate, inspiratory time, expiratory time, inspiratory to expiratory ratio, inspiratory flow, expiratory flow, tidal volume, minute volume, apnea duration, breath sounds—including rales, rhonchi, or stridor, changes in breath sounds, heart rate, heart sounds—including S1, S2, S3, S4, or murmurs, or changes in heart sounds, or the like. Some references that have common shorthand designations are referenced through such shorthand designations. For example, as used herein, HbCO designates carboxyhemoglobin, HbMet designates Methemoglobin, and Hbt designates total hemoglobin. Other shorthand designations such as COHb, MetHb, and tHb are also common in the art for these same constituents. These constituents are generally reported in terms of a percentage, often referred to as saturation, relative concentration or fractional saturation. Total hemoglobin is generally reported as a concentration in g/dL. The use of the particular shorthand designators presented in this application does not restrict the term to any particular manner in which the designated constituent is reported.
• Further, a greater emphasis has been put on decreasing the pain level of patients on the ward. Accordingly, patients are often given an IV setup that enables the patient to increase the level of analgesia at will. In certain situations, however, the patient's input must be ignored so as to avoid over medication. Complications from over sedation may include hypotension, tachycardia, bradycardia, hypoventilation and apnea. A physiological parameter system that uses pulse oximetry monitoring of SpO₂and pulse rate in conjunction with patient controlled analgesia (PCA) can aid in patient safety. Utilization of conventional pulse oximetry in conjunction with PCA, however, can result in the patient being erroneously denied pain medication. Conventional monitors are susceptible to patient motion, which is likely to increase with rising pain. Further, conventional monitors do not provide an indication of output reliability.
• Advanced pulse oximetry is motion tolerant and also provides one or more indications of signal quality or data confidence. These indicators can be used as arbitrators in decision algorithms for adjusting the PCA administration and sedation monitoring. Further, advanced pulse oximetry can provide parameters in addition to oxygen saturation and pulse rate, such as perfusion index (PI). For example, hypotension can be assessed by changes in PI, which may be associated with changes in pulse rate. Motion tolerant pulse oximetry is described in U.S. Pat. No. 6,206,830 titled Signal Processing Apparatus and Method; signal quality and data confidence indicators are described in U.S. Pat. No. 6,684,090 titled Pulse Oximetry Data Confidence Indicator, both of which are assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.
• One aspect of a physiological parameter system is a first parameter input responsive to a first physiological sensor and a second parameter input responsive to a second physiological sensor. A processor is adapted to combine the parameters and predetermined limits for the parameters so as to generate an indication of wellness.
• Another aspect of a physiological parameter system is a parameter input responsive to a physiological sensor and a quality indicator input relating to confidence in the parameter input. A processor is adapted to combine the parameter input, the quality indicator input and predetermined limits for the parameter input and the quality indicator input so as to generate a control output.
• A physiological parameter method comprises the steps of inputting a parameter responsive to a physiological sensor and inputting a quality indicator related to data confidence for the parameter. A control signal is output from the combination of the parameter and the quality indicator. The control signal is adapted to affect the operation of a medical-related device.
• A method of improving the reporting of a physiological parameter in a physiological parameter system comprises obtaining measurements of a physiological parameter from a measurement site. At least some of the physiological parameter measurements are maintained. A change in the measurement site is detected. A measurement of the physiological parameter from a new measurement site is obtained. The measurement of the physiological parameter at the new measurement site is compared with the maintained physiological parameter measurements. The magnitude of the physiological parameter reported by the physiological parameter system at the new measurement site is adjusted to approximately match the magnitude of the maintained physiological parameter measurements.
• A method of generating an indicator of patient wellness using a physiological parameter system includes receiving physiological parameter data from a sensor attached to the physiological parameter system. Physiological parameter preferences are provided to the physiological parameter system. The physiological parameter data is compared to the physiological parameter preferences. An indicator of patient wellness is generated by calculating a numerical wellness score based on the comparison.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates an embodiment of a physiological parameter measurement system.
• FIG. 2A illustrates an embodiment of a sensor assembly.
• FIGS. 2B-C illustrate alternative sensor embodiments.
• FIG. 3A illustrates an example chart of the value of a physiological parameter as measured by a sensor during a time when the sensor is moved from one measurement site to another.
• FIG. 3B illustrates a chart of a physiological parameter reported by a measurement system employing signal normalization techniques.
• FIG. 3C illustrates a chart of a MetHb reading which is smoothed to account for abnormal variations in the readings.
• FIG. 3D illustrates a MetHb smoothing flowchart.
• FIG. 3E illustrates a system of multiple different MetHb calculators which determine MetHb using different methods in order to calculate the most accurate MetHb reading.
• FIG. 4 is a block diagram of a physiological parameter system having signal normalization capability.
• FIG. 5 illustrates an embodiment of a method for normalizing a signal acquired by a sensor.
• FIG. 6 is a general block diagram of a physiological parameter system having alarm, diagnostic and control outputs.
• FIG. 6A illustrates an embodiment of aphysiological parameter system600 similar to the system inFIG. 6
• FIG. 7 is a block diagram of a physiological parameter system combining pulse oximetry and capnography and providing alarm outputs.
• FIG. 8 is a block diagram of a saturation limit alarm enhanced by ETCO₂measurements.
• FIG. 9 is a block diagram of a CO₂waveform alarm enhanced by SpO₂measurements.
• FIG. 10 is a block diagram of a physiological parameter system combining pulse oximetry and capnography and providing a diagnostic output.
• FIGS. 11A,11B,12 are block diagrams of a physiological parameter system utilizing pulse oximetry to control patient controlled analgesia (PCA).
• FIGS. 13,13A,13B illustrates an embodiment of a system that displays an indicator of the wellness of a patient.
• FIG. 14 is a flowchart showing an example method of displaying an indicator of the wellness of a patient.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• Hereinafter, various example embodiments of the present disclosure will be described in detail with reference to the attached drawings such that the present disclosure can be put into practice by those skilled in the art. However, the present disclosure is not limited to the example embodiments, but may be embodied in various forms.
• Some embodiments will be described in the context of computer-executable instructions, such as program modules, being executed by hardware devices, such as embedded processors, microcontrollers, and computer workstations. Program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of executable instructions or arrangement of associated data structures represents examples of corresponding acts for implementing the functions described in such steps. A person of skill in the art would understand that other structures, arrangements, and executable instructions could be used with the present disclosure without departing from the spirit thereof.
• FIG. 1 illustrates an embodiment of aphysiological measurement system100 having amonitor101 and asensor assembly101. Thephysiological measurement system100 allows the monitoring of a person, including a patient. In particular, the multiplewavelength sensor assembly101 allows the measurement of blood constituents and related parameters, including oxygen saturation, COHb, MetHb and pulse rate.
• In an embodiment, thesensor assembly101 is configured to plug into amonitor sensor port103.Monitor keys105 provide control over operating modes and alarms, to name a few. Adisplay107 provides readouts of measured parameters, such as oxygen saturation, pulse rate, COHb and MetHb to name a few.
• FIG. 2A illustrates a multiplewavelength sensor assembly201 having asensor203 adapted to attach to a tissue site, asensor cable205 and amonitor connector201. In an embodiment, thesensor203 is incorporated into a reusable finger clip adapted to removably attach to, and transmit light through, a fingertip. Thesensor cable205 and monitorconnector201 are integral to thesensor203, as shown. In alternative embodiments, thesensor203 can be configured separately from thecable205 andconnector201, although such communication can advantageously be wireless, over public or private networks or computing systems or devices, through intermediate medical or other devices, combinations of the same, or the like.
• FIGS. 2B-C illustrate alternative sensor embodiments, including a sensor211 (FIG. 2B) partially disposable and partially reusable (resposable) and utilizing an adhesive attachment mechanism. Also shown is asensor213 being disposable and utilizing an adhesive attachment mechanism. In other embodiments, a sensor can be configured to attach to various tissue sites other than a finger, such as a foot or an ear. Also a sensor can be configured as a reflectance or transflectance device that attaches to a forehead or other tissue surface. The artisan will recognize from the disclosure herein that the sensor can include mechanical structures, adhesive or other tape structures, Velcro wraps or combination structures specialized for the type of patient, type of monitoring, type of monitor, or the like.
• Certain physiological parameters and certain changes in physiological parameters may serve as indicators of an adverse condition affecting a patient. For example, an increase in blood methemoglobin (MetHb) concentration may be useful as a marker of the onset of sepsis or septic shock. As another example, measurements of high blood carboxyhemoglobin (COHb) concentration may indicate exposure to carbon monoxide (CO). Other physiological and related parameters to which techniques of the present disclosure may be applicable include respiration rate, respiration volume, oxygen saturation, pulse rate, ECG, blood glucose, blood pressure, temperature, perfusion index, exhaled carbon dioxide waveform, end tidal carbon dioxide, various signal quality indicators, data confidence indicators and trend data, among others.
• A sensor measuring a physiological parameter (e.g., a physiological parameter measurement device) of a patient may, under certain circumstances, detect a change in the magnitude of a detected signal that does not correspond to a change in the value of the physiological parameter. Such changes in a detected signal may occur, for example, when the sensor is moved to a different measurement site. Sometimes, a sensor may be temporarily removed from a patient, and medical reasons may compel movement of the sensor to a different location. For example, a multiple wavelength sensor may need to be moved to a different finger of a patient about every 12 hours in order to maintain the sensor's measurement effectiveness and/or to avoid injury to the patient. When the measurement site of a multiple wavelength sensor is switched to a different location, the magnitudes of some of the signals detected by the sensor may change, even though no significant change in the patient's physiological parameters has occurred during the brief sensor relocation period. Signal normalization techniques described in the present disclosure may reduce changes in physiological parameters reported by a physiological parameter system that are unrelated to actual physiological parameter variation.
• In some cases, the magnitude of a sensor measurement may be a less effective indicator of an adverse condition than a change in the magnitude of a sensor measurement. In such cases, a sensor may not need to be calibrated to report the absolute magnitude of a physiological parameter when changes in the magnitude of the parameter are more significant for purposes of condition detection. In other cases, the absolute magnitude of a physiological parameter is valuable, and a sensor signal must be analyzed and/or recalibrated to compensate for changes in the magnitude of the signal detected that do not correspond to changes in the value of the physiological parameter being measured. Signal normalization techniques may improve a physiological parameter system's reporting effectiveness for both types of parameters.
• FIG. 3A illustrates anexample chart300 of the value of a physiological parameter, such as, for example, MetHb, as measured by a sensor during a time when the sensor is moved from one measurement site to another. Chart300 shows the magnitude of a signal measured by a sensor as a function of time before any analysis or manipulation of the signal occurs. Afirst axis302 ofchart300 represents time, and asecond axis304 represents the magnitude of a signal, corresponding to a physiological parameter, detected at a point in time. The physiological parameter corresponding to the signal shown by way of example inFIG. 3A is blood MetHb concentration.
• Curve306 represents the magnitude of the signal detected by a sensor during a period when the sensor was at a first measurement site. The signal represented bycurve306 roughly oscillates about a nearly constant mean value of the signal. However, the signal may also follow any continuous increasing or decreasing trend and may also be nonoscillatory or contain a complex pattern of variation.
• At time T1 alongaxis302, the sensor is removed from the first measurement site.Curve308 represents the magnitude of the signal detected by the sensor while it is disconnected from the patient, for example, while a care provider switches the sensor to a new measurement site. Inchart300, the magnitude of the signal is about zero, but the sensor may continue to detect a signal of some nature (e.g., random noise, background interference, etc.) during a period when it is disconnected from a patient.
• At time T2 alongaxis302, the sensor is attached to a second measurement site on the patient. The second measurement site may be different than the first measurement site; for example, the second measurement site may be a different finger or a different position on a finger.Curve310 represents the magnitude of the signal detected by the sensor during a period when the sensor is at the second measurement site. The signal represented bycurve310 roughly oscillates about a nearly constant mean value of the signal that is higher than the mean value of the portion of the signal represented bycurve306. The difference between the magnitude of the signal shortly before time T1 and the magnitude of the signal shortly after time T2 is a shift in the magnitude of the signal that is related to the change in the measurement site. However, the shift in the signal may not correspond to an actual change in the value of a physiological parameter of the patient. In some cases, it may be safe to assume that the approximate value of a physiological parameter shortly before time T1 and shortly after time T2 is the same. In the absence of signal normalization, the signal shift may trigger a false alarm or cause a physiological parameter system to incorrectly report a change in a parameter. In the embodiment shown inFIG. 3A, reporting the non-normalized signal may trigger an alarm for sepsis or septic shock at time T2 due to an apparent increase in blood MetHb concentration.
• FIG. 3B illustrates achart350 of a physiological parameter reported by a measurement system employing signal normalization techniques. In the situation corresponding to chart350, it is assumed that the approximate value of the physiological parameter shortly before time T1 is the same as the approximate value of the physiological parameter shortly after time T2. Afirst axis352 ofchart350 represents time, and asecond axis354 represents the value of a physiological parameter reported by a physiological parameter system at a point in time. The physiological parameter shown by way of example inFIG. 3B is blood MetHb concentration.
• Inchart350,curve356 represents the value of the physiological parameter reported while the sensor is at the first measurement site.Curve358 represents the value of the physiological parameter reported while the sensor is not connected to the patient. In alternative embodiments, a physiological parameter system may not report a parameter or may shut off the sensor when the system detects that the sensor is not at a measurement site.Curve360 represents the value of the physiological parameter reported while the sensor is at the second measurement site. The physiological parameter data inchart350 is normalized because the value of the physiological parameter reported just before T1 is adjusted to match the value of the physiological parameter just after T2. Various methods of matching may exist, including adjusting the values before and after the measurement site change to be approximately equal, using data points before T1 to generate a trend line and fixing the data point at T2 to the trend line, or any other method known in the art of projecting or approximating the value of the physiological parameter at T2 based on data prior to T1.
• In some embodiments, sensor measurements that are received after time T2, as shown incurve310 of chart300 (FIG. 3A), may be normalized by adding an offset to the magnitudes of the measurements. The offset may be calculated by subtracting the magnitude of the non-normalized sensor measurement at time T2 from the magnitude of the normalized sensor measurement at T2. The offset may be a negative number. Similar methods of normalizing data points involving, for example, subtraction of an offset and other known methods may also be used. One result of signal normalization is that, given a relatively constant physiological parameter over time, the mean value ofcurve360 will more closely approximate the mean value ofcurve356. Signal normalization may reduce the incidence of false alarms and reports of changes in physiological parameters that have not in fact changed.
• FIG. 3C illustrates a further example of normalizing a signal with erratic noise, such as, for example, motion induced noise. As illustrated, aphysiological parameter signal370, such as a signal indicative of MetHb, is illustrated. Thephysiological parameter signal370 includes various inconsistencies, such as, for example,erratic noises371, probe offconditions373, and citechange conditions375. In order to deal with these inconsistencies, processing is used to determine anormalization377 or trend of the signal. Thenormalization377 uses various methods in order to determine a relatively stablephysiological parameter reading377.
• FIG. 3D illustrates a flow chart of anormalization procedure380. For ease in discussion,FIGS. 3D and 3E will be discussed with respect to a MetHb reading, however, it should be understood that any physiological parameter can be used with the present disclosure. The normalization procedure begins with the data signal381. As show, thenormalization feature380 includesMet calculator382; smoother384, Met signal extractor385;signal quality387 anddistortion388. In an embodiment, adata signal381 responsive to an intensity signal is input into theMet calculator382, and acurrent value383 of Met is calculated. Thecurrent value383 of Met, which in an embodiment is subject to noise, distortion, and site movements in the data signal381, is input into the smoother384, which reduces an error between thecurrent value383 of Met and actual MetHb conditions. For example, the smoother384 may advantageously determine a Met trend, and depending upon an indication of some or all of an amount of distortion, noise, signal quality, and/or waveform quality in the data signal383, substitute or combine the MetHb trend for or with thecurrent value383 to generate an output MetHb measurement.
• In an embodiment, thedistortion signal388 may comprise a Boolean value indicating whether the data signal383 includes, for example, motion-induced noise. Although an artisan will recognize from the disclosure herein a number of methodologies for deriving thedistortion signal388, derivation of a Boolean distortion signal is disclosed in U.S. Pat. No. 6,606,511, incorporated herein by reference. Alternatively, or in addition to, thesignal quality signal387 may comprise a Boolean value indicating whether the data signal383 meets various waveform criteria Although an artisan will recognize from the disclosure herein a number of methodologies for deriving thesignal quality signal387, derivation of a Boolean distortion signal is disclosed in the '511 patent. Alternatively, or in addition to, a feature extractor385 may advantageously producewaveform quality outputs386, indicative of waveform quality or waveform shape. Although an artisan will recognize from the disclosure herein a number of methodologies for deriving thewaveform quality signal386, derivation thereof is disclosed in U.S. Pat. No. 6,334,065, also incorporated herein by reference.
• Thus, the smoother384 accepts one or more or different indicators of the quality of the data signal381, and determines how to smooth or normalize the output to reduce errors between data trends and actual MetHb conditions. In an embodiment, the smoothing may advantageously comprise statistical weighting, other statistical combinations, or simply passing theMetHb measurement383 through to the output, depending upon one or more of the quality signals386,387,388, or logical combinations thereof.
• Upon the output of the normalized MetHb measurement, a monitor may advantageously audibly and/or visually presents the measurement to a caregiver, and when the measurement meets certain defined thresholds or behaviors, the monitor may advantageously audibly and/or visually alert the caregiver. In other embodiments, the monitor may communicate with other computing devices to alert the caregiver, may compare longer term trend data before alarming, or the like.
• FIG. 3E illustrates a simplified block diagram of an embodiment of aMetHb determination system390 using multiple Met calculation techniques. As shown,data391 is input into the system. Thedata391 is then routed to at least twodifferent Met calculators392,393. In an embodiment, more than two different types of calculation techniques can be used. The at least twoMet calculators392,393 output Met indications for input into theMet selector395. TheMet selector395 determines a Met value to output. The Met selector chooses the output based on which Met calculator works best for a given condition of the signal or based on which Met calculation fits the trend of Met readings. Other methods of selecting the best Met value can also be made as would be understood by a person of skill in the art from the present disclosure.
• FIG. 4 is a block diagram of a physiological parameter system having signal normalization capability. A physiological parameter system may include a sensorsignal analysis subsystem400 that implements signal normalization techniques.Signal analysis subsystem400 receives asignal402 from a physiological parameter measurement device output.Signal402 may be, for example, an electrical signal produced by an optical transducer within a pulse oximeter or a capnometer.
• In the embodiment shown inFIG. 4, signal402 is communicated to a sensor event module404. Sensor event module404 includes program code for detecting events that occur based on a pattern recognized insignal402. Detected events may include a change in measurement site, movement of the sensor, interference in the signal, etc. For example, sensor event module404 may determine that a measurement site of the sensor has been exchanged if a normal physiological parameter pattern ceases for a short period of time and then resumes. Alternatively, sensor event module404 may detect a measurement site switch whensignal402 is interrupted by an interval of random noise and/or a relatively large discontinuity in the signal. Alternatively, an operator can indicate an event, such as a location change, by, for example, pressing a predetermined function button. As another example, sensor event module404 may determine that signal normalization may not be appropriate when a sensor has been disconnected from a measurement site for a sufficiently long period of time (e.g., when an assumption that a signal trend will continue is no longer sound). Sensor event module404 may communicate signal402 and/or event information to asensor memory406 to store sensor signal pattern data for later use. Sensor event module404 may also communicatesignal402 and event information to signalnormalization module408.
• Sensor memory406 may retain a certain number ofsignal402 samples or may retain signal402 samples for a certain period. Retained samples may be used by program code insignal normalization module408 and/or sensor event module404. Samples fromsignal402 may be stored in a queue data structure, for example. In some embodiments, sensor event module404 may instructsensory memory406 to cease storing new samples when it determines that the sensor is not connected to a measurement site so that signal data for potential future signal normalization may be retained.Signal memory406 may also retain signal offset or calibration data.
• Signal normalization module408 comprises program code for converting asignal402 from a sensor output into a normalized measure of a physiological parameter. Program code inmodule408 may, for example, add or subtract a value fromsignal402 in order to eliminate shifts in the magnitude ofsignal402 that are not related to variation in a patient's physiological parameters.Signal normalization module408 may determine an offset that counterbalances a shift insignal402 that results from a change in sensor measurement site.Module408 may include program code for calculating a trend line from data stored insensor memory406. A trend line may be used to determine an appropriate value for a patient parameter when measurement resumes after an interruption insignal402.Module408 may also employ pattern recognition or signal transforms to help it determine how signal402 should be normalized. Sensor event module404 may triggersignal normalization module408 to reset its signal normalization when a certain signal events are detected. In some embodiments, sensor event module404 may communicate to signalnormalization module408 the retained signal data fromsensor memory406 it should use to calculate a new offset.Signal normalization module408 passes a normalizedsignal450 out ofsignal normalization subsystem400.
• Normalized signal450 may then be passed to other components of a physiological parameter system for further analysis and/or display. For example, normalizedsignal450 may be communicated to acomparator454 that compares signal450 to one or more parameter limits452. In some embodiments,comparator454 may generate analarm signal456 if normalizedsignal450 falls outside of parameter limits452.
• FIG. 5 illustrates an embodiment of a method for normalizing a signal acquired by a sensor when the measurement site of the sensor is changed. Atstep502, sensor memory406 (FIG. 4) maintains recent physiological parameter measurements received fromsensor output402. Sensor signal data may be passed directly tosensor memory406 for storage, or sensor event module404, for example, may select which signal samples will be retained and pass them tosensor memory406. Retained signal sample data may include the magnitude of the signal as well as an indicator of the time that the sample was taken and/or the order in which the sample was received. Alternatively,sensor memory406 may simply maintain signal data in chronological order in a queue, purging old sample data as new sample data is received. Data may be retained only for a certain time interval, such several seconds, a fraction of a minute, a minute, two minutes, or longer. The interval of retention may vary depending on the physiological parameter associated withsignal402. This step may continue until sensor event module404 detects a sensor measurement site change.
• Instep504 ofFIG. 5, sensor event module404 detects a change in the sensor measurement site. In some embodiments, sensor event module404 may detect the change in measurement site by one of the methods described with respect to the description of program code within sensor event module404 above. Alternatively, a user of a physiological parameter system may indicate that a change in sensor measurement site has occurred by means of a hardware or software interface. For example, the sensor may include a hardware switch that activates when the measurement site is changed. The system may also include a manual switch or button that a user can activate to cause sensor event module404 to register a change in the sensor measurement site. When sensor event module404 determines that sampling at the new measurement site has begun, the method proceeds to step506.
• Atstep506, signalnormalization module408 compares the magnitude of the signal sampled at the new measurement site with the magnitude of the retained signal that was obtained at the old measurement site.Signal normalization module408 may use pattern recognition or signal transform techniques to attempt to compare an oscillatory signal at similar points in its cycle to obtain a more accurate comparison. In some embodiments,module408 uses the comparison to calculate an offset that adjusts the signal at the time that measurement at the new measurement site begins to conform to a trend line fitted to signal data acquired from the old measurement site. Retained signal data from the old measurement site may be retrieved fromsensor memory406 and analyzed for the purpose of calibrating the sensor signal at the new measurement site. After the initial physiological parameter value is projected when the sensor begins sampling at the new measurement site, the method proceeds to step508.
• Instep508, signalnormalization module408 adjusts the magnitude of the signal measured at the new measurement site in order to output a normalizedsignal450. In some embodiments, adjusting the magnitude of the signal measured comprises modifying the magnitude of a signal measure measurement by adding or subtracting an offset. For example, the offset may be calculated by subtracting the magnitude of the signal sampled just after the sensor begins measurements at the new measurement site from the magnitude of the signal sampled just before the sensor was removed from the old measurement site. Alternatively, the offset may be defined as the difference between (1) a projected value of the magnitude of the signal just after the sensor begins measurements at the new measurement site, the projection based on measurements at the old measurement site, and (2) the actual measured value of the magnitude of the signal just after the sensor begins measurements at the new measurement site. Any other known means for calculating an offset may also be used.Signal normalization module408 continues to add or subtract the calculated offset until another normalization step is required. At the conclusion of the method shown inFIG. 5, the steps shown may be repeated as many times as changes in the measurement site of the sensor may require.
• Various embodiments of signal normalization techniques have been shown and described. Some alternative embodiments and combinations of embodiments disclosed herein have already been mentioned. Additional embodiments comprise various other combinations or alterations of the embodiments described.
• FIG. 6 illustrates aphysiological parameter system600, which may comprise an expert system, a neural-network or a logic circuit, for example. Thephysiological parameter system600 has asinputs601 from one or more parameters from one or more physiological measurement devices, such as apulse oximeter610 and/or acapnometer620. Pulse oximeter parameters may include oxygen saturation (SpO₂), perfusion index (PI), pulse rate (PR), various signal quality and/or data confidence indicators (Qn) and trend data, to name a few. Capnography parameter inputs may include, for example, an exhaled carbon dioxide waveform, end tidal carbon dioxide (ETCO₂) and respiration rate (RR). Signal quality and data confidence indicators are described in U.S. Pat. No. 6,108,090 cited above. Thephysiological parameter system600 may also have parameter limits606, which may be user inputs, default conditions or otherwise predetermined thresholds within thesystem600.
• Theinputs601 are processed in combination to generate one ormore outputs602 comprising alarms, diagnostics and controls. Alarms may be used to alert medical personnel to a deteriorating condition in a patient under their care. Diagnostics may be used to assist medical personnel in determining a patient condition. Controls may be used to affect the operation of a medical-related device.Other measurement parameters630 that can be input to the monitor may include or relate to one or more of ECG, blood glucose, blood pressure (BP), temperature (T), HbCO, MetHb, respiration rate and respiration volume, to name a few.
• FIG. 6A illustrates an embodiment of aphysiological parameter system600 similar to the system inFIG. 6. Thephysiological parameter system600 has asinputs601 from one or more parameters from one or more physiological measurement devices, such as, for example apulse oximeter610, an acousticrespiratory monitor640, anECG monitor650, an invasive or non-invasive blood pressure monitor650, a thermometer, or any other invasive or noninvase physiological monitoring devices or the like.
• FIG. 7 illustrates one embodiment of aphysiological parameter system700 combining pulseoximetry parameter inputs710 andcapnography parameter inputs720 so as to generate alarm outputs702. Parameter limits705 may be user inputs, default conditions or otherwise predetermined alarm thresholds for theseparameters710,720. Thealarms702 are grouped as pulse oximetry related730, capnography related740 and acombination750. For example, apulse oximetry alarm730 may be related to percent oxygen saturation and trigger when oxygen saturation falls below a predetermined percentage limit. Acapnography alarm740 may be related to ETCO₂and trigger when ETCO₂falls below or rises above a predetermined mm Hg pressure limit. Acombination alarm750 may indicate a particular medical condition related to both pulse oximetry and capnography or may indicate a malfunction in either instrument.
• FIG. 8 illustrates a SpO₂alarm embodiment800 that is responsive to ETCO₂. In particular, a SpO₂alarm805 may be triggered sooner and may indicate a high priority ifETCO₂803 is falling. That is, ifETCO₂803 is trending down above a certain rate, the SpO₂alarm805 is triggered at a higher percentage oxygen saturation threshold and alerts a caregiver to the possibility of a serious condition, e.g. a pulmonary embolism.
• As shown inFIG. 8, aslope detector810 determines theslope812 of the ETCO₂input803. Aslope comparator820 compares thisslope812 to apredetermined slope limit804. If the downward trend ofETCO₂803 is great enough, adelta value803 is added840 to the SpO₂lower limit802 to generate avariable threshold842. Athreshold comparator850 compares thisvariable threshold842 to the SpO₂input801 to generate atrigger852 for the SpO₂alarm805. The alarm volume, modulation or tone may be altered to indicate priority, based upon theslope comparator output822.
• FIG. 9 illustrates a CO₂alarm embodiment900 that is responsive to SpO₂. In particular, morphology of the input CO₂waveform901 is utilized to trigger analarm905, and that alarm is also responsive to a fallingSpO₂902. That is, if a pattern in the CO₂waveform is detected and SpO₂is trending down above a certain rate, then an alarm is triggered. For example, an increasing slope of the CO₂plateau in combination with a downward trend of SpO₂may trigger an alarm and alert a caregiver to the possibility of an airway obstruction.
• As shown inFIG. 9, apattern extractor910 identifies salient features in the CO₂waveform and generates acorresponding feature output912. Apattern memory920 stores one or more sets of predetermined waveform features to detect in the CO₂input901. Thepattern memory920 is accessed to provide afeature template922. Afeature comparator930 compares thefeature output912 with thefeature template922 and generates amatch output932 indicating that a specific shape or pattern has been detected in the CO₂waveform901. In addition, aslope detector940 determines theslope942 of the SpO₂input902. Aslope comparator950 compares thisslope942 to apredetermined slope limit904. If the downward trend ofSpO₂902 is great enough, a slope exceededoutput952 is generated. If both thematch output932 and the slope exceededoutput952 are each asserted or “true,” then a logical AND960 generates a trigger output96 to thealarm970, which generates analarm output905.
• FIG. 10 illustrates acombination embodiment1000 having adiagnostic output1005 responsive to bothSpO₂1001 andCO₂1003 inputs. A SpO₂slope detector100 determines the slope102 of the SpO₂input1001 and can be made responsive to a negative slope, a positive slope or a slope absolute value. Afirst comparator1020 compares this slope102 to a predetermined SpO₂slope limit1002. If the trend ofSpO₂1001 is great enough, a SpO₂slope exceededoutput1022 is asserted. Likewise, an CO₂slope detector1030 determines theslope1032 of the CO₂input1003. Asecond comparator1040 compares thisslope1032 to a predetermined CO₂slope limit1004. If the downward trend ofCO₂1001 is great enough, an CO₂slope exceededoutput1042 is asserted. If both slope exceededoutputs1022,1042 are asserted or “true,” adiagnostic output1005 is asserted.
• In one embodiment, theslope detectors610,1030 are responsive to a negative trend in theSpO₂1001 andCO₂1003 inputs, respectively. Accordingly, thediagnostic output1005 indicates a potential embolism or cardiac arrest. In another embodiment, the SpO₂slope detector610 is responsive to negative trends in theSpO₂1001 input, and the CO₂slope detector1030 is responsive to a positive trend in theCO₂1003 input. Accordingly, thediagnostic output1005 indicates a potential airway obstruction. Thediagnostic output1005 can trigger an alarm, initiate a display, or signal a nursing station, to name a few.
• FIGS. 11A-B illustrate aphysiological parameter system1100 utilizing pulse oximetry to control patient controlled analgesia (PCA). In particular embodiments, acontrol output1108 is responsive topulse oximetry parameters1101 only ifsignal quality1103 is above apredetermined threshold1104. InFIG. 11A, thecontrol output1108 can be used to lock-out patient controlled analgesia (PCA) if pulse oximetry parameter limits have been exceeded. If signal quality is so low that those parameters are unreliable, however, PCA is advantageously allowed. That is, the pulse oximeter parameters are not allowed to lock-out PCA if those parameters are unreliable. By contrast, inFIG. 11B, thecontrol output1108 can be used to advantageously lock-out or disable patient controlled analgesia (PCA) if pulse oximetry parameter limits have been exceeded or if signal quality is so low that those parameters are unreliable.
• As shown inFIG. 11A,pulse oximetry parameters1101 andcorresponding limits1102 for those parameters are one set of inputs and asignal quality measure1103 and a correspondinglower limit1104 for signal quality are another set of inputs. Theparameters1101 andcorresponding limits1102 generate a combinedoutput1202 that is asserted if any of the pulse oximetry parameter limits are exceeded. Acomparator1110 compares thesignal quality1103 input with alower limit1104 generating aquality output1112 that is asserted if thesignal quality1103 drops below thatlimit1104. An ANDlogic1120 generates areset1122 if the combinedoutput1202 is asserted and thequality output1112 is not asserted. Thereset1122 resets thetimer1130 to zero. Acomparator1140 compares thetimer output1132 to apredetermined time limit1106 and generates atrigger1142 if the time limit is exceeded. Thetrigger1142 causes thecontrol1150 to generate thecontrol output1108, enabling a patient controlled analgesia (PCA), for example. In this manner, the PCA is enabled if all monitored parameters are within set limits and signal quality is above its lower limit for a predetermined period of time.
• As shown inFIG. 11B, the combinedoutput1202,quality output1112, reset1122,timer1130,comparator1140 andcontrol1150 are generated as described with respect toFIG. 11A, above. An ORlogic1121 generates areset1122 if either the combinedoutput1202 or thequality output1112 is asserted. In this manner, the PCA is disabled for a predetermined period of time if any of the monitored parameters are outside of set limits or the signal quality is below its lower limit.
• FIG. 12 illustrates combinedlimits1200 having SpO₂parameters1101 andcorresponding thresholds1102 as inputs and providing acombination output1202. In particular, if anyparameter1101 exceeds itscorresponding limit1102, the output of thecorresponding comparator1210,1220,1240 is asserted. An ORlogic1250 is responsive to any assertedoutput1212,1222,1242 to asserted the combinedoutput1202. For example, the combinedoutput1202 may be asserted ifSpO₂1201 falls below alower limit1209, pulse rate (PR)1203 rises above anupper limit1204 orPR1203 falls below a lower limit120.
• A physiological parameter system has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in the art will appreciate many variations and modifications. For example, the control output1108 (FIG. 11B) can be used to control (titrate) delivered, inspired oxygen levels to patients based upon pulse oximetry parameters, unless signal quality is so low that those parameters are unreliable. One of ordinary skill in the art will also recognize that the control output1108 (FIG. 11B) can be used to control patient delivery of any of various pharmacological agents and/or medical gases.
• FIG. 13 illustrates an embodiment of asystem1300 that displays an indicator of the wellness of a patient. Various sensors1302a-1302ncommunicate with aparameter analysis module1306. Sensors1302a-1302nmay include pulse oximeters and capnometers, among other physiological parameter measurement devices.Sensor1302noutputs a signal that may be sampled, normalized, and/or analyzed by modules that are not shown insystem1300 before being passed toparameter analysis module1306. As described above, normalization of sensor signals before comparison of the signals to parameter limits452 (FIG. 4) and/orparameter preferences1304 may have certain benefits, such as decreased incidence of false alarms and/or more effective determination of the wellness of the patient.
• In the embodiment shown, a user may provideparameter preferences1304 toparameter analysis module1306 through a user interface.Parameter preferences1304 may include preferred ranges, less preferred ranges, least preferred ranges, upper limits, lower limits, preferred rates of increase or decrease, preferred patterns or trends, preferred states, or any combination of such preferences or other standards for evaluating the desirability of various physiological parameter values and signals. In some cases, a user ofsystem1300 may provide custom preferences to override a default set ofphysiological parameter preferences1304 preprogrammed intosystem1300. In some embodiments,parameter analysis module1306 may include program code for dynamically changing or suggesting changes to various parameter preferences as a function of certain physiological parameters or related sensor performance data.
• Parameter analysis module1306 compares at least some of the signal data received from sensors1302a-1302ntoparameter preferences1304 in order to calculate an indicator of the wellness of a patient. In some embodiments, the indicator calculated is a numerical indicator; for example, a number between one and ten, where a ten corresponds to a patient with a high level of wellness, and a one corresponds to a patient with a very low level of wellness as depicted inFIG. 13B. Other ranges, such as one to 100, −100 to 100, etc., and scales, such as an alphabetic A-F scale or a color scale, may also be used including the scale depicted inFIG. 13A. Other indicators that may be generated byparameter analysis module1306 include graphical indicators of potential trouble areas, gauges, charts, level meters, and the like may also be used.Parameter analysis module1306 communicates the indicator to adisplay1308, which may display the indicator in any suitable graphical or textual form that is known in the art. For example,display1308 may show a number of bars or a level meter, the number of which may correspond to one of the numerical indicator scales discussed above.
• FIG. 14 is a flowchart showing an example method of displaying an indicator of the wellness of a patient. Atstep1402, parameter analysis module1306 (FIG. 13) receives signal data from one or more sensors1302a-1302n.As discussed previously, such signal data may be normalized or otherwise modified from its raw form before being passed toparameter analysis module1306.Parameter analysis module1306 may continuously update an indicator as new data is received and may calculate averages, variances, and/or other analytical measures of various physiological parameters over time. In some embodiments,parameter analysis module1306 may update the indicator of patient wellness only periodically, sporadically, or by request rather than continuously, thus requiring only occasional reception of data from sensors1302a-1302n.
• Instep1404,parameter analysis module1306 receivesparameter preferences1304.Preferences1304 may by received only once or sporadically as a user supplies custom preferences.Preferences1304 may also be received and/or updated continuously when, for example,parameter preferences1304 are functions of various physiological or sampling parameters.
• Atstep1406,parameter analysis module1306 compares the data received from sensors1302a-1302ntoparameter preferences1304. Individual sensor measurements may be compared toparameter preferences1304, or parameter analysis module may compareparameter preferences1304 to a moving average of sensor measurements, for example. Comparison of various other known analytical measures of sensor data is also possible and within the scope of the present disclosure. The comparison performed byparameter analysis module1306 may include magnitude comparisons, pattern analysis, and/or trend analysis. Historical sensor data may also be used in the comparison.
• Instep1408 ofFIG. 14,parameter analysis module1306 generates an indicator of the wellness of the patient based on the comparison performed instep1406. The indicator may be in any of the forms discussed previously. For example,module1306 may increase a wellness score (e.g., a numerical indicator of wellness) when physiological parameters fall within preferred ranges or when sensor signals follow preferred patterns and/or trends. The indicator may comprise a simple or a more detailed textual and/or graphical summary of the patient's wellness as interpreted from parameters measured by sensors1302a-1302n.In some embodiments, the indicator may be a scaled number in combination with a textual description of the patient's wellness score and/or conditions that may be affecting the score. In addition, particular a particular condition affecting the patient can also be generated for communication to a healthcare provider, such as, for example, sepsis, septic shock, apnea, heart failure, airway obstruction, carbon monoxide poisoning, low oxygen content, etc.
• Afterparameter analysis module1306 generates the wellness indicator, it sends the indicator to display1308 atstep1410.Display1308 may be integrated withphysiological parameter system1300 or may be a separate display device. The display may also include auditory sounds, such as for example, beeps, voices, words, etc., to indicate a particular event or condition occurring.
• Although the foregoing invention has been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art from the disclosure herein. Additionally, other combinations, omissions, substitutions and modifications will be apparent to the skilled artisan in view of the disclosure herein. It is contemplated that various aspects and features of the invention described can be practiced separately, combined together, or substituted for one another, and that a variety of combination and subcombinations of the features and aspects can be made and still fall within the scope of the invention. Furthermore, the systems described above need not include all of the modules and functions described in the preferred embodiments. Accordingly, the present invention is not intended to be limited by the recitation of the preferred embodiments, but is to be defined by reference to the appended claims.

Claims (10)

1. A method of providing cohesive physiological parameter trend data through a change in measurement site, the method comprising:

obtaining measurements of a physiological parameter from a first measurement site of a patient and determining trend information from the measurements of the physiological parameter from the first measurement site during a first time period;

obtaining measurements of the physiological parameter from a second measurement site of a patient and determining trend information from the measurements of the physiological parameter from the second measurement site during a second time period different from the first time period;

determining a physiological trend offset for the second trend information based on the trend information from the first measurement site.

2. The method ofclaim 1, wherein the physiological parameter comprises a met-hemoglobin measurement.

3. The method ofclaim 1, wherein the trend offset is a difference in magnitude between two adjacent-in-time measurements, where one of the adjacent-in-time measurements is taken at the first site and the second adjacent-in-time measurements is taken from the second site.

4. The method ofclaim 3, wherein the offset is a negative value.

5. The method ofclaim 3, wherein at least one of the two adjacent-in-time measurements is normalized.

6. A method of measuring a physiological parameter in a physiological parameter system comprising:

obtaining measurements of a physiological parameter from a first measurement site of a patient;

determining a change in the measurement site of the patient;

obtaining a measurement of the physiological parameter from a second measurement site of the patient;

comparing the measurement of the physiological parameter at the second measurement site with the measurement from the first measurement site; and

calibrating the physiological parameter measurements at the second site with the physiological measurements at the first site.

7. The method ofclaim 6, wherein calibrating comprises adding an offset to the measurement of the physiological parameter at the second measurement site.

8. The method ofclaim 7, wherein the offset is calculated by subtracting the measurement of the physiological parameter at the second measurement site with the most recent physiological parameter measurement from the first site.

9. The method ofclaim 7, wherein the offset is calculated by subtracting the measurement of the physiological parameter at the second measurement site with a projection of the physiological parameter at the second measurement site extrapolated from a trend line fit to the physiological parameter measurements of the first site.

10-20. (canceled)

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