DETECTION QF SITE OXIMETRY DEGRADATION
Background
[0001] In medicine, a plethysmograph is an instrument that measures variations in the size of an organ or body part on the basis of the amount of blood passing through or present in the part. An oximeter is a type of plethysmograph that determines the oxygen saturation of the blood. One common type of oximeter is a pulse oximeter.
[0002] A pulse oximeter is a medical device that indirectly measures the oxygen saturation of a patient's blood (as opposed to measuring oxygen saturation directly through a blood sample) and changes in blood volume in the skin.
[0003] A pulse oximeter includes a light sensor that is placed at a site on a patient, usually a fingertip, toe, forehead or earlobe, or in the case of a neonate, across a foot. Light, which may be produced by a light source integrated into the pulse oximeter, containing both red and infrared wavelengths is directed onto the skin of the patient and the light that passes through the skin is detected by the sensor. The intensity of light in each wavelength is measured by the sensor over time. The graph of light intensity versus time is referred to as the photoplethysmogram (PPG) or, more commonly, simply as the "pleth." From the waveform of the PPG, it is possible to identify the pulse rate of the patient and when each individual pulse occurs. In addition, by comparing the intensities of two wavelengths when a pulse occurs, it is possible to determine blood oxygen saturation of hemoglobin in arterial blood. This relies on the observation that highly oxygenated blood will relatively absorb more red light and less infrared light than blood with a lower oxygen saturation.
Summary
[0004] This disclosure describes systems and methods for detecting degradation in performance of pulse oximeter due to site degradation. As discussed in greater detail below, long term use of a pulse oximeter at a site can lead to conditions which may impair the pulse oximetry measurement and reduce the performance of the pulse oximeter. This disclosure describes systems and methods for improving the quality of pulse oximetry measurements taken over time by detecting when a site on a patient has degraded to the extent that it is recommended that the measurements be taken from another location on the patient. In an embodiment, this is done by providing an expanded amount of memory for recording pulse oximetry data for an extended period of time. The data is then periodically evaluated to determine if one or more of the characteristics of the data exhibits a trend indicating a deteriorating quality due to site degradation. If such a trend is detected, a notification recommending that the pulse oximeter be moved to a different site is generated.
[0005] Among other things, the disclosure describes a pulse oximeter comprising a light detector and a site degradation analysis engine. The light detector generates unfiltered data based on an intensity of light received, which data being used to generate a current oxygen saturation measurement for the patient to whom it is attached. The site degradation analysis engine, upon determination that the light detector has been at the same location for at least a predetermined period of time, analyzes the unfiltered data and, based on results of the analysis, generates an alarm.
[0006] The disclosure also describes a method for improving oximetty measurements from a pulse oximeter measuring oxygen saturation of a patient's blood the method includes analyzing pulse oximetty data obtained during a period of time from the pulse oximeter at a first location on a patient and, based on results of the analysis, recommending that the pulse oximeter be moved to a different location on the patent. The method may further include receiving the pulse oximetry data from the pulse oximeter; storing the pulse oximetry data for the period of time in memory at least until performing the analyzing operation; and deteimining that the pulse oximeter has been at the first location on the patient for the period of time prior to performing the analysis. [0007] The disclosure further describes a method for measuring oxygen saturation of a patient's blood. The method includes directing light from a light source into tissue of a patient and for a predetermined period of time, measuring with a detector the light emanating from the tissue of the patient at a first location. The data indicative of the light emanating from the tissue of the patient at the first location is recorded. In addition, the oxygen saturation of the patient's blood is calculated based on a subset of data, the subset of data containing the most recent data. The method also includes inspecting the data for a trend indicating that a characteristic of the light emanating from the tissue of the patient at the first location has changed due to degradation of the first location over the predetermined period of time. If such a trend is detected, the method includes generating a notification recommending that the detector be moved to a second location different from the first location.
[0008] These and various other features as well as advantages which characterize the disclosed systems and methods will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features of the systems and methods described herein are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the disclosed technology as claimed.
Brief Description of the Drawings
[0010] The following drawing figures, which form a part of this application, are illustrative of disclosed technology and are not meant to limit the scope of the description in any manner, which scope shall be based on the claims appended hereto.
[0011] FIG. 1 is a perspective view of a pulse oximetry system, according to an embodiment. [0012] FIG. 2 is a block diagram of the embodiment of a pulse oximetry system of FIG. 1 coupled to a patient.
[0013] FIG. 3 is a flow chart of an embodiment of a method for determining when to change locations on a patient from which pulse oximetiy measurements are taken. [0014] FIG. 4 is a block diagram illustrating some of the components of a pulse oximetry system that detects site degradation, according to an embodiment.
Detailed Description
[0015] This disclosure describes systems and methods for improving the quality of pulse oximetry measurements taken over time by detecting when a site on a patient has degraded to the extent that it is recommended that the measurements be taken from another location on the patient. In an embodiment, this is done by providing an expanded amount of memoiy for recording pulse oximetiy data for an extended period of time. The data is then periodically evaluated to determine if one or more of the characteristics of the data exhibits a trend indicating a deteriorating quality due to site degradation. If such a trend is detected, a notification recommending that the pulse oximeter be moved to a different site is generated. [0016] Pulse oximetry is often performed over long periods of time. However, a pulse oximetry site on a patient (e.g., a finger, toe, forehead, etc. on which a pulse oximeter is attached and taking blood oxygen saturation measurements from) may become less suitable for such measurements over time. This degradation may be caused by one of many factors or a combination of factors. Such factors include exsanguination of the tissue from which the pulse oximetry, which may be caused by the continued pressure of the pulse oximeter on the site. Exsanguination can lead to a reduction in the pulse amplitude seen on the plethysmogram making it more difficult to differentiate between signals received during a pulse and signals received between pulses, which has a direct effect on the ability of the pulse oximeter to determine an accurate blood oxygen saturation measurement.
[0017] In addition, depending on how it is attached a pulse oximeter may restrict the ability of the tissue to adequately expand in response to pulses, which may cause the pulse shape (e.g., as seen on the plethysmogram) to be altered. Alteration of the pulse shape can make it more difficult for a pulse oximetry system to identify the pulse rate and when each pulse occurs, thus introducing additional error in the oxygen saturation measurements. [0018] Although the techniques introduced above and discussed in detail below may be implemented for a variety of medical devices, the present disclosure will discuss the implementation of these techniques in a pulse oximetry system. The reader will understand that the technology described in the context of a pulse oximetry system could be adapted for use with other systems such as a combined medical monitoring system that utilizes pulse oximetiy data. [0019] FIG. 1 is a perspective view of an embodiment of a pulse oximetiy system 10. The system 10 includes a sensor 12 and a pulse oximetiy monitor 14. The sensor 12 includes an emitter 16 for emitting light at one or more wavelengths into a patient's tissue, A detector 18 is also provided in the sensor 12 for detecting the light originally from the emitter 16 that emanates from the patient's tissue after passing through the tissue. The emitter 16 and detector 18 may be on opposite sides of a digit such as a finger or toe, in which case the light that is emanating from the tissue has passed completely through the digit. In an alternative embodiment, the emitter 16 and detector 18 may be arranged so that light from the emitter 16 penetrates the tissue and is reflected by the tissue into the detector 18, such as a sensor designed to obtain pulse oximetry data from a patient's forehead.
[0020] The monitor 14 may be configured to calculate physiological parameters received from the sensor 12 relating to light emission and detection. Further, the monitor 14 includes a display 20 configured to display the physiological parameters, other information about the system, and/or alarm indications. In the embodiment shown, the monitor 14 also includes a speaker 22 to provide an audible alarm in the event that the patient's physiological parameters are not within a normal range, as defined based on patient characteristics. The sensor 12 is communicatively coupled to the monitor 14 via a cable 24. However, in other embodiments a wireless transmission device (not shown) or the like may be utilized instead of or in addition to the cable 24.
[0021] In the illustrated embodiment, the pulse oximetry system 10 also includes a multiparameter patient monitor 26. The multi-parameter patient monitor 26 may be configured to calculate physiological parameters and to provide a central display 28 for information from the monitor 14 and from other medical monitoring devices or systems (not shown). For example, the multiparameter patient monitor 26 may be configured to display a patient's oxygen saturation reading generated by the pulse oximetiy monitor 14 (referred to as an "SpO2" reading) and pulse rate information from the monitor 14 and blood pressure from a blood pressure monitor (not shown) on the display 28. Additionally, the multi-parameter patient monitor 26 may emit a visible or audible alarm via the display 28 or a speaker 30, respectively, if the patient's physiological characteristics are found to be outside of the normal range. The monitor 14 may be communicatively coupled to the multi-parameter patient monitor 26 via a cable 32 or 34 coupled to a sensor input port or a digital communications port, respectively. In addition, the monitor 14 and/or the multi-parameter patient monitor 26 may be connected to a network to enable the sharing of information with servers or other workstations (not shown).
[0022] FIG. 2 is a block diagram of the exemplary pulse oximetiy system 10 of FIG. 1 coupled to a patient 40 in accordance with present embodiments. Specifically, certain components of the sensor 12 and the monitor 14 are illustrated in FIG. 2. The sensor 12 includes the emitter 16, the detector 18, and an encoder 42. In the embodiment shown, the emitter 16 is configured to emit at least two wavelengths of light, e.g., RED and IR, into a patient's tissue 40. Hence, the emitter 16 may include a RED light emitting light source such as the RED light emitting diode (LED) 44 shown and an IR LED 46 for emitting light into the patient's tissue 40 at the wavelengths used to calculate the patient's physiological parameters. In certain embodiments, the RED wavelength may be between about 600 nm and about 700 nm, and the IR wavelength may be between about 800 nm and about 1000 nm.
[0023] Alternative light sources may be used in other embodiments. For example, a single wide-spectrum light source may be used, and the detector 18 may be configured to detect light only at certain wavelengths. In another example, the detector 18 may detect a wide spectrum of wavelengths of light, and the monitor 14 may process only those wavelengths which are of interest. It should be understood that, as used herein, the term "light" may refer to one or more of ultrasound, radio, microwave, millimeter wave, infrared, visible, ultraviolet, gamma ray or X-ray electromagnetic radiation, and may also include any wavelength within the radio, microwave, infrared, visible, ultraviolet, or X-ray spectra, and that any suitable wavelength of light may be appropriate for use with the present techniques.
[0024] In an embodiment, the detector 18 may be configured to detect the intensity of light at the RED and IR wavelengths. In operation, light enters the detector 18 after passing through the patient's tissue 40. The detector 18 converts the intensity of the received light into an electrical signal. The light intensity is directly related to the absorbance and/or reflectance of light in the tissue 40. That is, when more light at a certain wavelength is absorbed or reflected, less light of that wavelength is received from the tissue by the detector 18. After converting the received light to an electrical signal, the detector 18 sends the signal to the monitor 14, where physiological parameters may be calculated based on the absorption of the RED and IR wavelengths in the patient's tissue 40. An example of a device configured to perform such calculations is the Model NόOOx pulse oximeter available from Nellcor Puritan Bennett LLC. [0025] The encoder 42 may contain information about the sensor 12, such as what type of sensor it is (e.g., whether the sensor is intended for placement on a forehead or digit) and the wavelengths of light emitted by the emitter 16. This information may be used by the monitor 14 to select appropriate algorithms, lookup tables and/or calibration coefficients stored in the monitor 14 for calculating the patient's physiological parameters.
[0026] In addition, the encoder 42 may contain information specific to the patient 40, such as, for example, the patient's age, weight, and diagnosis. This information may allow the monitor 14 to determine patient-specific threshold ranges in which the patient's physiological parameter measurements should fall and to enable or disable additional physiological parameter algorithms. The encoder 42 may, for instance, be a coded resistor which stores values corresponding to the type of the sensor 12, the wavelengths of light emitted by the emitter 16, and/or the patient's characteristics. These coded values may be communicated to the monitor 14, which determines how to calculate the patient's physiological parameters and alarm threshold ranges. In another embodiment, the encoder 42 may include a memory on which one or more of the following information may be stored for communication to the monitor 14: the type of the sensor 12; the wavelengths of light emitted by the emitter 16; the proper calibration coefficients and/or algorithms to be used for calculating the patient's physiological parameters and/or alarm threshold values; the patient characteristics to be used for calculating the alarm threshold values; and the patient-specific threshold values to be used for monitoring the physiological parameters, [0027] Signals from the detector 18 and the encoder 42 may be transmitted to the monitor 14. In the embodiment shown, the monitor 14 includes a general-purpose microprocessor 48 connected to an internal bus SO. The microprocessor 48 is adapted to execute software, which may include an operating system and one or more applications, as part of performing the functions described herein. Also connected to the bus 50 are a read-only memory (ROM) 52, a random access memory (RAM) 54, user inputs 56, the display 20, and the speaker 22. [0028] The RAM 54 and ROM 52 are illustrated by way of example, and not limitation. Any computer-readable media may be used in the system for data storage. Computer-readable media are capable of storing information that can be interpreted by the microprocessor 48. This information may be data or may take the form of computer-executable instructions, such as software applications, that cause the microprocessor to perform certain functions and/or computer-implemented methods. Depending on the embodiment, such computer-readable media may comprise computer storage media and communication media, Computer storage media includes volatile and non- volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM5 EPROM, EEPROM, flash memory or other solid state memory technology, CD- ROM, DVD, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by components of the system. [0029] In the embodiment shown, a time processing unit (TPU) 58 provides timing control signals to a light drive circuitry 60 which controls when the emitter 16 is illuminated and multiplexed timing for the RED LED 44 and the IR LED 46. The TPU 58 also controls the gating-in of signals from detector 18 through an amplifier 62 and a switching circuit 64. These signals are sampled at the proper time, depending upon which light source is illuminated. The received signal from the detector 18 may be passed through an amplifier 66, a low pass filter 68, and an analog-to-digital converter 70. The digital data may then be stored in a queued serial module (QSM) 72 (or buffer) for later downloading to the RAM 54 as the QSM 72 fills up. In one embodiment, there may be multiple separate parallel paths having the amplifier 66, the filter 68, and the A/D converter 70 for multiple light wavelengths or spectra received. [0030J The microprocessor 48 may determine the patient' s physiological parameters, such as Spθ2 and pulse rate, using various algorithms and/or look-up tables based on the value of the received signals corresponding to the light received by the detector 18. Signals corresponding to information about the patient 40, and particularly about the intensity of light emanating from a patient's tissue over time, may be transmitted from the encoder 42 to a decoder 74. These signals may include, for example, encoded information relating to patient characteristics. The decoder 74 may translate these signals to enable the microprocessor to determine the thresholds based on algorithms or look-up tables stored in the ROM 52. The encoder 42 may also contain the patient- specific alarm thresholds, for example, if the alarm values are determined on a workstation separate from the monitor 14. The user inputs 56 may also be used to enter information about the patient, such as age, weight, height, diagnosis, medications, treatments, and so forth. In certain embodiments, the display 20 may exhibit a list of values which may generally apply to the patient, such as, for example, age ranges or medication families, which the user may select using the user inputs 56. The microprocessor 48 may then determine the proper thresholds using the user input data and algorithms stored in the ROM 52. The patient-specific thresholds may be stored on the RAM 54 for comparison to measured physiological characteristics. [0031] FIG. 3 illustrates an embodiment of a method for measuring the oxygen saturation of a patient's blood. The method 300 is directed to determining when a site on a patient is no longer suitable for pulse oximetry due to site degradation. This is fundamentally different from alarms used in pulse oximetiy due to lost signals and poor data quality, as the determination that a site has degraded and should be changed may be made even though an accurate and acceptable pulse oximetiy measurement is still being obtained by the pulse oximeter.
[0032] The method 300 starts with the installation of the pulse oximeter at a site on the patient in an installation operation 302. As discussed above, such a site (which may alternately be referred to as a location) may include a digit, the forehead or some other site from which a pulse oximeter can obtain an oxygen saturation measurement. The installation operation 302 includes attaching the pulse oximeter to the site and initiating the oxygen saturation measurement. As discussed above, this includes directing of light from a light source into tissue of a patient and measuring with a detector the light emanating from the tissue of the patient at the monitoring site. [0033] The installation operation 302 is then followed by a period of oxygen saturation measurements in an ongoing monitoring operation 304. In the monitoring operation 304, the pulse oximeter is used to monitor the oxygen saturation of the patient's blood by monitoring the light detected emanating from the monitoring site. The monitoring may be continuous, periodic, of even occasional depending upon the medical needs at the time. However, the monitoring is ongoing and lasts for an extended period of time.
[0034] During the monitoring operation 304, the oxygen saturation of the patient's blood is calculated based on the most recent data received from the sensor in order to provide a current measurement of the oxygen saturation. As is known in the art, the current oxygen saturation may be displayed in real time and analyzed based on patient characteristics. For example, the current measurements may be compared to thresholds if the measurements exceed a threshold range or amount various alarms may be triggered.
[0035] During the monitoring operation 304, in addition to the monitoring of the current oxygen saturation and its subsequent display to the medical caregivers, the method 300 also records at least some of the data received from the pulse oximeter. The data recorded may be filtered or unfϊltered data. In addition, not all data received from the detector of the pulse oximeter may be stored, but rather only a subset a data may be stored as necessaiy to perform a later analysis to determine if site degradation is occurring.
[0036] The method 300 further determines how long a pulse oximeter has been located at a site, which is illustrated by the determination operation 306. hi an embodiment, the determination operation 306 only performs the site degradation analysis in situations when a pulse oximeter has been installed in the same location for an extended period of time. Such an extended period of time may be determined by a user- or manufacturer-selected threshold. For example, a user may be provided with an interface that allows the user to select one of set of threshold time periods. Alternatively a user may be allowed to enter a user time. In an embodiment, threshold time periods upon which to perform site degradation analyses may be selected from at least thirty minutes, at least an hour, at least two hours, at least three hours, at least four hours, at least six hours, at least 12 hours and at least 24 hours. [0037] The determination operation 306 may include analyzing the data received during the monitoring operation 304 for discontinuities and gaps indicating that the pulse oximeter has fallen off or been relocated. Alternatively, a pulse oximetiy system may be provided with a means for a caregiver to indicate when the site has been changed and this information may be used to determine if the site has changed. In an embodiment, if the determination operation 306 determines that a site has been changed prior to reaching the selected threshold time period for degradation analysis, the method resets and the timer begins again. This is illustrated by the flow control line returning to the monitoring operation 304, If a change in site location is detected, the system may or may not automatically delete the stored data from the previous location. [0038] However, if the determination operation 306 determines that the site has been in continuous use for the threshold period of time, an analysis operation 308 is performed. In the analysis operation 308, the data recorded during the monitoring operation 304 is inspected for a trend indicating that a characteristic of the light emanating from the tissue of the patient at the first location has changed due to degradation of the first location over the predetermined period of time.
[0039] If such a trend is detected (illustrated by the second determination operation 312), then a notification operation 310 is performed in which an alarm or some other notification is generated indicating to the operator or caregiver that the sensor should be moved to a second location on the patient different from the current site. Such a notification could be any type of alarm, display or message. In addition, in an embodiment a user or operator may select the type of notification to be generated upon a detection of site degradation.
[0040] If the analysis does not determine that the site is degrading or the trend indicates that the site has degraded enough to generate a notification, then after a waiting period (illustrated by wait operation 314) the analysis operation 308 is performed again, but only if the oximeter has not been moved in the interim.
[0041] Note that the monitoring operation 304 is ongoing and uninterrupted by the determination operation 306, the analysis operation 308 and the notification operation 310. Thus, if the notification is ignored, the oximeter will continue to monitor the oxygen saturation of the patient.
[0042] The analysis operation 308 may analyze the recorded data to identify changes in one or more characteristics of the recorded data between the time the sensor was installed and the current time or, alternatively, over some fixed period of time (e.g., the last 12 hours). In an embodiment, these changes may then be compared to a threshold range or amount and if the detected changes exceed the appropriate threshold, the notification operation 310 is performed. [0043] It should be noted that the window over which the data is analyzed need not be fixed to the threshold period for analysis. This is particularly important when noting that the analysis operation 308 may be periodically repeated as long as the sensor remains at the same location. For example, in an embodiment an operator may select that the analysis operation 308 be performed only when the pulse oximeter has been installed at a site for more than 12 hours. Subsequent to this occulting, the analysis operation 304 may be repeated every hour, e.g., the wait period used in the wait operation 314 is selected to be one hour. Such subsequent analysis operations 308 may analyze all of the data received since the oximeter was installed at the site or, alternatively, analyze on some predetermined subset of data such as the most recent 6 hours of data, most recent 12 hours of data, the most recent and least recent data, etc. [0044] The amount of data analyzed in any given analysis operation 308 may be determined by user selection or limited by the amount of internal memory provided for storing the data or both. For example, an analysis scheme may be used that only compares the first hour's worth of data from a site to the most recent hour's worth of data in an embodiment in which the data storage capacity is limited to only two hour's worth of data. Alternatively, in embodiments in which there is sufficient data storage capacity all data obtained since the oximeter was installed at the site may be analyzed.
[0045] The analysis operation 304 may include one or more different analyses of the recorded data. For example, in an embodiment, the analysis includes identifying changes in one or more characteristics such as the SpO2 measurement, the pulse amplitude of one or more of the signals from the sensor, the signal strength of one or more of the signals from the sensor, and the pulse shape as indicated by the signals from the sensor.
[0046] An analysis of the SpO2 measurement may include comparing the measurements taken at the beginning of the time period being analyzed and those taken at the end. Alternatively, the analysis could include a mathematical analysis of how the SpO2 measurements have changed over time. The results of the comparison or mathematical analysis may then be compared to a benchmark or threshold in order to determine if the SpO2 measurements taken over time indicate that the site is degrading as a location for taking pulse oximetry measurements. [0047] An analysis of the pulse amplitude may include comparing the pulse amplitudes observed at the beginning of the time period being analyzed and those taken at the end. Alternatively, the analysis could include a mathematical analysis of how the pulse amplitudes have changed over time, hi addition, the pulse amplitudes of the RED and IR signals could be independently analyzed and then compared to each other. The results may then be compared to a benchmark or threshold in order to determine if the pulse amplitudes have changed over time to the extent that they indicate that the site is degrading. In an embodiment, a decrease in pulse amplitude of 10%, 15%, 20% or 25% over the time period may be chosen as the threshold that when exceeded (i.e., the measurement falls out of the acceptable range as indicated by the threshold) indicates that the site has degraded and a notification may be generated. [0048] An analysis of the signal strength may include comparing the signal strengths observed at the beginning of the time period being analyzed and those taken at the end. Alternatively, the analysis could include a mathematical analysis of how the signal strength has changed overtime, hi addition, the signal strength of the RED and IR signals could be independently analyzed and then compared to each other. The results may then be compared to a benchmark or threshold in order to determine if the pulse amplitudes have changed over time to the extent that they indicate that the site is degrading. For example, in an embodiment a decrease in the ratio RED to IR signal strength of 10%, 15%, 20% or 25% over the time period may be chosen as the threshold that when exceeded indicates that the site has degraded and a notification may be generated. [0049] The signal strength analysis could also take into account the strength of the signal provided to the light emitter. For example, embodiments of pulse oximeters can vaiy the signal strength used to drive the light emitters in order to compensate for different patients and placements on the patient's body. In such embodiments, the relative change of signal strength of the detected light emanating from the patient to that provided to the light emitter may be analyzed for changes indicating site degradation. For example, in an embodiment a decrease in the ratio detected to emitted signal strength for a selected wavelength of light of 5%, 10%, 15%, 20% or 25% over the time period may be chosen as the threshold that when exceeded indicates that the site has degraded and a notification may be generated.
J0050] An analysis of the pulse shape may include comparing the pulse shapes observed at the beginning of the time period being analyzed and those taken at the end. Alternatively, the analysis could include a mathematical analysis of how the pulse shapes have changed over time, hi addition, the pulse shapes of the RED and IR signals could be independently analyzed and then compared to each other. The results may then be compared to a benchmark or threshold in order to determine if the pulse shapes have changed over time to the extent that they indicate that the site is degrading. Alternatively, the pulse shapes may be compared to a representative pulse shape that is indicative of constricted arteries or other physical manifestations of a degraded site. In an embodiment, a pulse shape that differs, based on a mathematical comparison, from a representative shape of 10%, 15%, 20% or 25% over the time period may be chosen as the threshold that when exceeded (i.e., the measurement falls out of the acceptable range as indicated by the threshold) indicates that the site has degraded and a notification may be generated. [0051] As mentioned above, in alternative embodiments filtered data, unfiltered data or both filtered and unfiltered data may be analyzed in the analysis operation 308. Unfiltered data may be useful in detecting characteristics that would be filtered out in the process of obtaining an accurate SpO2 measurement. For example, in an embodiment the 2nd, 3rd and 4th harmonics in the data may be determined mathematically and the results compared to a predetermined threshold, Determination of such harmonics would be altered if filtered versus unfiltered data were used. [0052] The thresholds used in the analysis operation 308 to determine if a site has degraded may be empirically determined by prior experiments on patients. In addition, different thresholds may be used depending on the characteristics of the patient and the needs and preferences of the caregiver. For example, in an embodiment a threshold or thresholds may be selected so that a notification is generated at even the slightest indication of a degraded site. Alternatively, in an embodiment a threshold or thresholds may be selected so that a notification is generated only if it appears based on the trend of data that failure to be able to accurately measure the oxygen saturation of the blood of the patient from this site is eminent.
[0053] FfG. 4 is a block diagram illustrating some of the components of a pulse oximetiy system that detects site degradation. In the embodiment shown, the system 400 includes a sensor 402 containing a light emitter 404 and a light detector 406; and, in a separate housing 418, a processor 408, a site degradation analysis engine 410; an oxygen saturation engine 412; and a memoiy 414. A display 416 is also provided. The sensor 402 and its components operate as described previously with reference to FfG. 2.
[0054] The memoiy 414 may include RAM, flash memoiy or hard disk data storage devices. The memory stores data, which may be filtered or unfiltered data, received from the detector 406. The data may be decimated, compressed or otherwise modified prior to storing in the memoiy 414 in order to increase the time over which data may be retained.
[0055] The oxygen saturation engine 412 generates a current oxygen saturation measurement from the data generated by the sensor. In an embodiment, the oxygen saturation engine 412 is a dedicated hardware circuit that may include filters, firmware comprising lookup tables or other data, and its own processor (not shown) that allow it to generate the current oxygen saturation measurement. In an alternative embodiment, the oxygen saturation engine 412 may be implemented as a software application that is executed, in whole or in part, by the system processor 408. In yet another embodiment, functions described herein as being performed by the oxygen saturation engine 412 may be distributed among hardware, software and firmware throughout the system 400 and its other components.
[0056] The site degradation analysis engine 410, upon determination that the light detector 406 has been at the same location for at least a predetermined period of time, analyzes the unfiltered data, filtered data and/or a combination of both filtered and unfiltered data and, based on results of the analysis, generates an alarm to the display 416.
[0057J The display 416 may be any device that is capable of generating a audible or visual notification. The display need not be integrated into the other components of the system 400 and could be a wireless device or even a monitor on a general purpose computing device (not shown) that receives email or other transmitted notifications from the site degradation analysis engine
410.
[0058] It will be clear that the described systems and methods are well adapted to attain the ends and advantages mentioned as well as those inherent therein. Those skilled in the art will recognize that the methods and systems described within this specification may be implemented in many manners and as such is not to be limited by the foregoing exemplified embodiments and examples. In other words, functional elements being performed by a single or multiple components, in various combinations of hardware and software, and individual functions can be distributed among software applications and even different hardware platforms. In this regard, any number of the features of the different embodiments described herein may be combined into one single embodiment and alternate embodiments having fewer than or more than all of the features herein described are possible.
[0059] While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the described technology. For example, depending on the data available from the patient additional or different characteristics of the pulse oximetry data may be analyzed. For instance, if actual blood oxygenation measurements are being periodically taken from blood removed from the patient, this data may be correlated over time against the SpO2 data in order to identify changes due to site degradation,
[0060] Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.