WO2008149081A2 - Système d'oxymétrie de pouls - Google Patents

Système d'oxymétrie de pouls Download PDF

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Publication number
WO2008149081A2
WO2008149081A2 PCT/GB2008/001898 GB2008001898W WO2008149081A2 WO 2008149081 A2 WO2008149081 A2 WO 2008149081A2 GB 2008001898 W GB2008001898 W GB 2008001898W WO 2008149081 A2 WO2008149081 A2 WO 2008149081A2
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WO
WIPO (PCT)
Prior art keywords
sensor
data
light
blood oxygen
monitoring system
Prior art date
Application number
PCT/GB2008/001898
Other languages
English (en)
Other versions
WO2008149081A3 (fr
Inventor
Geoffrey Mathews
Veronica Hickson
Original Assignee
The Electrode Company Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Electrode Company Limited filed Critical The Electrode Company Limited
Publication of WO2008149081A2 publication Critical patent/WO2008149081A2/fr
Publication of WO2008149081A3 publication Critical patent/WO2008149081A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
    • G01N21/274—Calibration, base line adjustment, drift correction
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
    • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
    • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
    • A61B5/1495—Calibrating or testing of in-vivo probes
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/08—Sensors provided with means for identification, e.g. barcodes or memory chips
    • A61B2562/085—Sensors provided with means for identification, e.g. barcodes or memory chips combined with means for recording calibration data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N2021/3144—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths for oxymetry

Definitions

  • the current invention is related to a pulse oximetry system, the recognition of sensors that are used in the field of pulse oximetry, and compensation for patient specific parameters and factors in this field.
  • the system enables not only SpO 2 but also a value for the total oxygen concentration of the blood to be obtained.
  • Pulse oximetry is used in medicine every day to assess the amount of oxygen in a patient's blood. The measurement is based on the amount of haemoglobin in the arteries that carry oxygen (cO 2 Hb).
  • cO 2 Hb haemoglobin in the arteries that carry oxygen
  • FO 2 Hb fractional oxyhaemoglobin
  • SO 2 functional oxygen saturation
  • SpO 2 is the estimate of SaO 2 made by pulse oximeter equipment but more often this value is referred to as SATs, or the SATs value.
  • SATs oxyhaemoglobin concentration
  • cHHb deoxyhaemoglobin
  • Pulse oximetry is an indirect measurement; it is a measurement by proxy. On its journey from the lungs to the mitochondria oxygen travels through arteries, arterioles, capillaries, intercellular fluid, intra cellular fluid, and finally arrives at the mitochondria. Pulse oximetry indicates the proportion of the haemoglobin, being delivered to the capillary bed, which is carrying oxygen. If this value is within expected ranges, then it is assumed that the oxygen supply is reaching the required destination in sufficient quantity throughout the tissues.
  • SATs value there are situations where pulse oximetry can indicate an adequate SATs value, yet this has little relationship to oxygen available to the tissues. For example a pulse oximeter may show a normal SATs value of 97%, but if the patient is anaemic, i.e. there is low haemoglobin, then the SATs value does not necessarily reflect the oxygen available to the tissues.
  • the oxygen concentration of the blood is the amount of oxygen carried in each 100ml of blood. This is a combination of the oxygen in solution and the oxygen carried by the haemoglobin.
  • Oxygen concentration O 2 in solution + O 2 carried by Haemoglobin
  • SpO 2 is percentage saturation of Haemoglobin with oxygen
  • Hb is the haemoglobin concentration in grams per 100 ml of blood
  • PaO 2 is the partial pressure of oxygen in the artery (generally considered as
  • haemoglobin present in various diseases and conditions.
  • non-functional haemoglobin does not carry oxygen
  • foetal haemoglobin has a different affinity for oxygen binding and releasing oxygen at lower pressures of oxygen.
  • Oxygen available to the tissue depends not only on the blood oxygen concentration but also on the release of oxygen by the oxyhaemoglobin.
  • Factors such as haemoglobin type, pH, 2,3- diphosphoglycerate (2,3 -DPG), temperature and tissue oxygen concentration will alter the amount of oxygen released and delivered.
  • the movement of the oxygen dissociation curve by various factors is called the Bohr Shift.
  • a typical known pulse oximetry system consists of a sensor, such as a probe/transducer, that is applied to the patient and generates a signal and a monitor, which contains the means for processing and displaying the signal.
  • the sensors that are used comprise a device that is placed on the finger, ear, toe, or forehead of a patient and red light and infrared light is emitted from light emitting diodes in the sensor and the light passes through the skin of the patient. The absorption of the red and infrared light is detected by a pulse oximeter monitor and the values for the red and infrared ratio are recorded and this provides what is called the R- value for the sensor.
  • Sensors are generally, but not always, detachable from the monitor to enable cleaning, maintenance and replacement, and can be either disposable or reusable.
  • the disposable sensors are intended for single use only and the re-useable sensors often do not last longer than twelve months.
  • Sensors are often designed for use at a specific site, such as ear, finger, toe, forehead, or on a particular patient type such as adult, foetal, paediatric. The accuracy of the entire system can be improved if the sensor can be identified and linked to a particular R curve or calibration data appropriate for a particular sensor application site and/or patient parameters.
  • the manufacturer's main income is often derived from the sale of sensors rather than the sale of monitors themselves.
  • the rearward compatibility of pulse oximeter sensors that is the ability of pulse oximeter sensors to work with older monitors, is an important feature in the pulse oximeter market.
  • Replacement sensors are available from the original equipment manufacturer (OEM) and authorised suppliers, and from third party manufacturers (unauthorised suppliers). Often unauthorised sensors can be bought at a lower price, which can be an attractive option to health authorities that are on a budget but this potentially has a major impact on patient safety.
  • Unauthorised sensors as well as often being cheaper than OEM sensors may be of a lower quality than the OEMs and are not always correctly configured to work with a particular OEM monitor.
  • clinical and engineering staff can have difficulty in determining if a sensor in use is an OEM/authorised sensor or an unauthorised sensor.
  • staff in hospital supplies maybe swayed by the lower price incentive of an unauthorised sensor, without realizing the ramifications with regard to compatibility with a particular monitor and patient safety.
  • the sensor quality may be affected by the quality of the materials and/or the fact that the construction of the sensor is poor. This variation in sensor quality can manifest itself as variations in the spectral properties of the sensor resulting in a compromise in accuracy. Poor quality construction and insulating materials can result in partial and total electrical shorts within the sensor cable. For example inadequate screening and partial shorts and open circuits can impinge on the reliability and accuracy of the sensor when in use. It is possible for a partial short to go undetected by the monitor and the operator continues to use the senor unaware that the sensor is faulty. If the fault happens to increase the noise signal on the photo diode wires in the sensor the monitor will tend to towards the low 80s %, regardless of what the true SATs value of the patient might be.
  • unauthorised sensors are also not always configured correctly to enable them to work satisfactorily with a particular OEM monitor.
  • the monitor cannot detect spectral errors resulting from poor quality sensors and without access to special support equipment users have no way of knowing the accuracy of the sensor that they are using.
  • Pulse oximeter calibration is achieved by carrying out clinical breathe downs trials with a sensor of a particular type and specification with a group of volunteers. This data is then stored in the monitor in software form.
  • patient parameters such as blood constituents will also cause variations in the R-curve data and errors can be introduced due to these differences.
  • parameters such as red cell count, red cell volume, haematocrit, functional haemoglobin types and concentration, dysfunctional haemoglobin types and concentration etc. These parameters may be obtained by other analysis of the patient in addition to information obtained through pulse oximetry, pulse CO oximetry etc.
  • the prior art does not address the problems of accurately recognizing sensors and validating those sensors and/or restricting unauthorized sensors using optical characteristics. Further, the prior art does not enable a monitor once a sensor has been optically recognised to provide optimal calibration data or R curve information for that particular type of sensor and/or the intended application site on the patient and/or patient parameters. Furthermore the present invention seeks to enable the user to take an ideal R curve for that sensor and then further refine that data according to patient parameter, such as male/female, presence of melanin, patient size, type and concentration of haemoglobin such as foetal haemoglobin, sickle haemoglobin, non-functional haemoglobins etc. Summary of the Invention
  • the present invention provides a blood oxygen monitoring system comprising a processor for processing an input from a light sensor device, the processor receiving an input relating to one or more patient specific parameters and determining an output based on the light sensor device input and the patient specific parameter input.
  • the present invention therefore enables variations in patient specific parameters to be taken into account for a pulse oximetry technique.
  • the system includes a wavelength sensitive device (such as, for example an interferometer or spectrometer).
  • a wavelength sensitive device such as, for example an interferometer or spectrometer.
  • the wavelength sensitive device may be used to derive spectral data, for example for R curve modification or generation in line with techniques described herein and our related PCT patent application publication WO2008/035076.
  • the wavelength sensitive device may be a device separate and distinct from the light sensor device. In other embodiments the wavelength sensitive device may act as the sensor device.
  • the processor determines an output based on the input from the wavelength sensitive device and the patient specific parameter input. In this way it is possible to factor in patient related parameters and also any adjustment required based upon spectral characteristics of specific light sources.
  • the system includes a monitoring device for monitoring or measuring the patient specific parameter.
  • the monitoring device for monitoring or measuring the patient specific parameter provides a direct input to the processor.
  • processed data from the monitoring device for monitoring or measuring the patient specific parameter may be communicated to the processor (e.g .by wireless communication means or a wire electronic link or fibre optic link).
  • the monitoring device for monitoring or measuring the patient specific parameter comprises a wavelength sensitive device, which may be the same wavelength sensitive device that is used for determining the specific spectral characteristics of the LED's.
  • the light may be delivered from the patient to the light sensor device via an optical fibre.
  • light may be delivered via an optical fibre to a wavelength sensitive device in the system in order to monitor, measure or detect the relevant patient parameter.
  • the relevant patient parameter input is used to select a processing adjustment factor using system stored data relating to the patient parameter.
  • system stored data may relate to breathe down trials for high melanin patients.
  • the relevant patient parameter input is used to select a processing adjustment factor for using with a system stored R curve.
  • relevant patient parameter input is used to generate data representative of an R curve.
  • the R curve generation beneficially additionally involves input relating to spectral data provided from a system wavelength sensitive device.
  • the processor calculates total oxygen calculation , as a result of a system input into the processor relating to blood haemoglobin level or concentration.
  • the system includes a sensor having one or more light emitter(s), preferably arranged to emit an optical recognition signal that can be detected by a monitor and used to identify said sensor.
  • the invention provides a method of calibrating a blood oxygen monitoring system, comprising determining an adjustment factor required to be applied in producing an system output, wherein the adjustment factor is determined taking into account one or more patient specific parameters.
  • a sensor adapted for use in pulse oximetry, said sensor including one or more light emitter(s), arranged to emit an optical recognition signal that can be detected by a monitor and used to identify said sensor.
  • the one or more light emitter(s) is one or more of integral light emitter(s) used also used to emit light that is used to detect blood characteristics.
  • the one or more light emitter(s) is one or more dedicated light emitter(s) separate from the integral light emitter(s).
  • the optical recognition signal can be generated by existing light emitters in the sensor and/or by separate light emitters, which provides the option of using optical recognition for existing sensors or for the production of new types of sensors. Having more recognition signals or a combination of signals is a further way of preventing the use of unauthorised sensors.
  • the optical recognition signal is generated as an optical signal that is identifiable as being distinct from any other optical signals generated by the sensor.
  • the signal may be a unique dedicated signal that is generated separately from other signals that are produced by the sensor.
  • the signal is an existing signal that is analysed in a unique way for recognising the sensor.
  • the signal is an existing signal that has been altered so that it has unique characteristics that can be used as a means of identifying the sensor.
  • the light emitter for the optical recognition signal is in the form of one or more LEDs which emits light with specified frequency characteristics which can be monitored and used to identify the sensor.
  • the senor includes a controller or control system that can operate on the one or more light emitters to control the characteristics of the optical recognition signal.
  • the control system is provided as an active device that can influence the characteristics of the integral or the dedicated light emitter or emitters to produce one or more unique characteristics for the light emitted from said light emitters and hence the optical recognition system that results is provided as a unique tag for the sensor with which it is associated.
  • the characteristics that may be altered are one or more of wavelength, frequency or possibly the duration and timing of the light emitted to give signals that alter in duration or pulse frequency.
  • a Nellcor sensor can be recognised by the combination of LEDs including for example Red 663nm, and Infra red 905nm, and a small secondary emission in the red at about 890-900nm.
  • a Datex-Ohmeda GE sensor can be recognised by the presence a separate and third LED, always in the IR range. 905nm would indicate that the sensor is to be used with an Ohmeda system. 940nm would indicate that the sensor is to be used with a Datex system. It is such signals that can be identified and recognised by the current invention for the purpose of distinguishing between known authorised sensors and unknown unauthorised sensors.
  • a sensor is provided with a signal having spectral properties that are unique to that sensor or group of sensors and which can be used to tag and identify a particular group of sensors.
  • the senor includes one or more controllers that control the characteristics of the light being emitted from one or more of the light emitters, thereby altering the characteristics of the optical recognition signal.
  • the controller or controllers can control the frequency, the pulse duration, the frequency of pulse or the wavelength of the light emitted, or any combination thereof. This provides for variation in the characteristics of the optical recognition signal so that a manufacturer or in some cases the user can provide the signal with a tailored recognition signal for a particular sensor.
  • the senor includes a timing arrangement wherein a first optical signal is emitted to provide the optical recognition signal to identify the sensor, with the timing mechanism controlling light emission by the sensor to provide a time lag after which a second optical signal is emitted by the sensor that is used to measure blood flow, oxygen saturation etc.
  • the senor includes a data carrier that holds data that can be used to identify the sensor.
  • the data may be in the form of the manufacturer's details, such as name and address, the batch code, manufacturing code or date of manufacture. The provision of such data allows for the identification and authentification of individual sensors.
  • the data carrier may be integral with the controller or it may be a separate element that interacts with the controller or each controller if there is more than one controller.
  • the data carrier may be provided as a microchip or a memory card that holds the data.
  • the data may be embedded permanently on the data carrier in the form of a read only (ROM) memory, so that no alterations may be made to the data. This means that when sensors are produced, the data carriers in the sensor hold fixed data about the sensor, which cannot be altered. If for some reason there is a requirement that sensors have particular features that are not recognised as being associated with a particular sensor, for example if there are new legal requirements for the use of sensors, then if this data cannot be recognised on the sensor, the operator is alerted to the fact when the sensor is identified and prevented from using that particular sensor because it is now obsolete. The user may be alerted by an alarm device present on the sensor or in the monitor or device that is used to identify the sensor.
  • ROM read only
  • the data carrier may be arranged such that it can be updated with new information regarding the sensor, for example, if there are upgrades in information concerning the sensor, such as a manufacturers, name and address or operating information, there may be facilities, whereby individuals may be able to upgrade data onto the data carrier.
  • access to the data carrier is restricted by having encryption codes so that only authorized individuals may upgrade the data on the data carrier.
  • the date of recognition and R curve calculation is stored on the active device so that calibration/R curve calculation is not requested each time that the sensor is used with that monitor.
  • this may be incorporated in existing sensors as a retrofitted new safety feature, or it can be incorporated in new sensors as they are manufactured.
  • the data carrier is integral with the optical emitter for the optical recognition signal.
  • the inclusion of the data carrier with the sensor again makes for a new device which has the added value of providing a unique sensor including data that allows for verification as to the authenticity of the sensor and gives complete traceability of manufactured products, which adds to patient safety.
  • the monitor or sensor or associated device may include an alarm that is activated if the optical recognition signal is not recognised by a monitoring system or device used with the sensor.
  • the alarm may also be integrated in the sensor or it can be provided as a separate element attachable to the sensor.
  • the alarm that is emitted may be audible, visual or it can be a combination of both.
  • the data carrier is a plug in element that can be attached to the sensor as required.
  • An example of such a data carrier would be a memory stick that could include new data concerning the sensor, for example manufacturer's details or batch codes.
  • the light emitter for the optical recognition signal is in the form of an LED which emits light with specified frequency characteristics which can be monitored and used to identify the sensor.
  • the light emitter produces an optical recognition signal as a number of flashes to indicate serial number, and a particular type of sensor. These flashes could be generated by the red LED individually, the IR LED, or a combination of all LEDs.
  • a method of identifying a sensor for use in pulse oximetry whereby an emitter connected with the sensor is caused to emit light which provides an optical recognition signal, said light being collected and identified by a light receiver associated with the sensor.
  • the light receiver may be incorporated in the sensor itself, which then transmits data to a monitor that can verify the data concerning the sensor.
  • the data may be transmitted by cable, fibre optics or by wireless connection.
  • the light receiver may be incorporated into a stand-alone device or interface device or a monitor for a pulse oximeter that holds data relating to individual sensors.
  • the stand-alone device, interface or monitor then uses that data to verify whether the sensor is an authorised sensor.
  • controllers that are operable to influence the characteristics of the optical recognition signal emitted from the integral or the dedicated light emitter or emitters.
  • the controllers are pre-programmed to set the characteristics or alternatively, the controller is adjustable to alter the characteristics of the light emitted and hence the optical recognition signal that is generated.
  • the characteristics altered are one or more of the wavelength, frequency, pulse-duration or pulse frequency of optical recognition signal.
  • the method includes a timing mechanism, whereby a first optical signal is emitted to provide the optical recognition signal to identify the sensor, with the timing mechanism controlling light emission by the sensor to provide a time lag after which a second optical signal is emitted by the sensor that is used to measure blood flow, oxygen saturation etc.
  • the optical recognition signal is generated by a dedicated light emitter, separate from the light emitter that emits a second optical signal used to measure blood flow, oxygen saturation, etc.
  • the optical recognition signal is generated by a light emitter that is either an existing or part of an existing light emitter in the sensor.
  • the method includes operation of a reader to identify data held by a data carrier incorporated in the sensor to identify data held on said data carrier relating to the sensor.
  • the method includes writing new data onto a data carrier to upgrade information about said sensor.
  • a pulse oximetry system including a sensor with an optical recognition signal generator and a pulse oximeter having a monitor that can recognise and identify said sensor.
  • a controller adapted to be used with a sensor according to the invention.
  • the controller or controllers can control the frequency, the pulse duration the frequency of pulse or the wavelength of the light emitted, or any combination thereof.
  • a method for calibration of a pulse oximeter monitor said method, involving recognising a sensor to be used with a pulse oximeter by recognition of an optical signal, using the optical recognition signal to identify the sensor, matching data regarding the characteristics of the sensor with those in a data bank which identifies characteristics regarding a sensor and introducing a correction value for the sensor that can be used to monitor the blood oxygen saturation values and or blood characteristics etc of a patient.
  • the correction values take into account one or more of the specific patient's parameters e.g. age, sex, melanin levels, haemoglobin types, haemoglobin concentration etc.
  • the correction value is a deviation value calculated as the difference between recognised value and an expected value for a SAT reading.
  • the correction value is based on R-values.
  • the R values can be calculated using a calibration apparatus discussed in the co-pending UK Patent Application No: 0618547.4 where there is provided a calibration apparatus for use in calibrating a monitoring apparatus used in determining the oxygen content of blood, said calibration apparatus including a wavelength sensitive device to receive data relating to at least one radiation wavelength from said sensor and a processor for determining an adjustment factor calculated from said data concerning said at least one radiation wavelength of radiation which can be used to calibrate said monitoring apparatus.
  • a value for the total oxygen concentration of the blood can be calculated and provided to the user.
  • the apparatus and method of the present invention have particular applications in improving the performance of pulse oximetry because the use of light recognition systems reduces the risk of errors associated with the use of microchips or resistors and provides a more accurate way of identifying sensors.
  • optical recognition of sensors has the advantage that once a sensor is identified, it is possible to use this identification in the calibration of a monitor for use with a particular sensor taking into account variations in characteristics that may be associated with that sensor taken from known data. This means that pulse oximetry measurements and total oxygen content of the blood calculations can be carried out accurately for individuals, taking into account parameters such as sex, ethnic group, age, haemoglobin type and quantity etc.
  • the present invention can be used for recognizing a wide range of sensor types as well as being used in the calibration of monitors to individual sensors for special applications and patient parameters.
  • the types of sensors which the invention is applicable to includes:
  • Figures Figure 1 shows: a schematic diagram of a wavelength sensitive device according to an embodiment of the invention
  • Figure 2 shows: a flow diagram of the operation of a sensor recognition system according to an embodiment of the invention
  • Figure 3 shows: a spectral characteristic of a light emitter for a sensor according to an embodiment of the invention
  • Figure 4 shows: a graph used in the calibration of a monitor using a sensor based on deviation from expected SAT values
  • Figure 5 shows: a graph used in the calibration of a monitor using R-curves
  • Figure 1 shows a spectral sensitive monitor 300 for displaying signals received from a sensor 100.
  • the sensor comprises one red light emitting diode (LED) and one infrared light emitting diode (not shown),
  • LED red light emitting diode
  • the absorption A of the red and infrared radiation is influenced by factors such as the tissues through which the light is passed, e.g. in the finger, the foot or else where in the body.
  • the amount of melanin in the tissue and also the blood volume and other blood parameters will also affect the absorption.
  • the monitor will have a wavelength sensitive device 310 such as a spectrometer or an interferometer.
  • the device 310 is shown as being incorporated in the monitor but is could be an add-on attachment.
  • the wavelength sensitive device is calibrated using a light source 320.
  • the wavelength sensitive device is then used to monitor light emitted from the sensor 100.
  • the light emitted from a light source within the sensor can be used by the wavelength sensitive device to recognise the sensor, which is attached to the monitor.
  • the light from the sensor is fed to the wavelength sensitive device by an optically opaque finger 330 that is attached to the monitor on a permanent or temporary basis, or by means of an optical fibre that forms part of the sensor.
  • Light emitted from light sources such as LEDs associated with the sensor will provide optical recognition signals that can be detected by the monitor. This data can be compared with data held in the memory of the monitor or which has been downloaded onto the memory of the monitor. The monitor will then compare characteristics such as the spectral properties of the light emitted from the sensor and compare those values with data that is held for known sensors. If the spectral characteristics do not match those with the known values, then the user will be alerted to the fact that the sensor is probably not an authorised sensor, and the user can choose to check the batch number with the manufacturer or supplier.
  • the monitor is turned on if not already turned on and the sensor 100 (shown in Figure 1) is attached to the monitor 300 (again shown in Figure 1) by plugging the plug end of the sensor into the socket in the monitor.
  • This action causes a command signal to be sent to the micro-controller in the sensor from the monitor and a predetermined digital code step A(I) stored on the micro-controller contains the sensor's unique identity, and information regarding the type of sensor.
  • the signal generated in this embodiment is an optical signal and can be seen as step B in the Figure.
  • the command byte tells the micro-controller to send its internal ID information regarding sensor serial number, sensor type, and calibration status to the IR led in the sensor.
  • An LED in the sensor creates a pulse (for example the Infrared light emitter in the sensor).
  • the pulse is detected by a detector in the sensor and the fact that the pulse is detected is relayed back to the monitor.
  • This step can be seen as C in the figure.
  • step F If calibration for the sensor spectral characteristics is required then this takes place as step F before proceeding to data entry for specific patient parameters step H.
  • the system can go straight to step H and data can be entered for specific patient parameters If the signal from the micro-controller in the sensor is not recognised the sensor is not recognised and the monitor will not proceed to use the sensor.
  • an audible and or visible alarm is activated wither on the sensor or the monitor to alert the user to the fact that the sensor may not be operating correctly or may not be an authorised sensor and the operator can then take steps to check the authenticity of the status or whether it is working properly and this is shown as step E in the Figure. Additionally the user may be allowed to decide to continue using the sensor with the monitor.
  • the senor is checked to see if it is an older type authorised sensor not fitted with a micro-controller.
  • the authorisation check may also involve checking the spectral properties of the sensor by means of the spectral sensitive monitor.
  • Step F If a sensor is not recognised as authorised, then either the user is warned of the presence of an unauthorised sensor and the user is given the option of still going ahead with the calibration process (Step F) or alternatively, the sensor is rejected completely and the user is not allowed to go ahead with the calibration of the sensor and the monitor at all (Step G).
  • This provides an ultimate failsafe mechanism to prevent operation, for example where less skilled users may be using the monitor who may not be able to make the necessary adjustments in any calibration system.
  • the sensor and monitor can be adjusted to take these features into account when calibrating the sensor.
  • This extra calibration stage can be seen as I in the Figure.
  • the system can proceed directly to a state of being ready for use as represented by J.
  • An example of the type of spectral characteristics from an LED of a sensor can be seen in Figure 3.
  • An Authorised Nellcor sensor can be recognised by the wavelengths of the red (662nm - 671nm) and IR (907nm) emissions, and the presence of a secondary peak generated by the red LED at about 890nm - 900nm. Unauthorised Nellcor type sensors do not have the secondary peak.
  • Authorised Datex-Ohmeda sensors are uniquely fitted with two IR LEDs to enable them to work with both Datex and Ohmeda systems.
  • the presence of this third IR LED can be used to distinguish authorised Datex-Ohmeda sensors from unauthorised sensors.
  • optical characteristics of light emitters can be used to identify sensors for use in pulse oximetry is a unique feature of the invention because the significance of these characteristics has not be recognised as a way of positively identifying sensors. Instead, to date systems have been devised to remove variations in frequency characteristics to avoid spectral abnormalities.
  • the wavelength sensitive device 310 is calibrated using the spectral lines of a Neon- Argon (Ne-Ar) light source 320.
  • the Ne-Ar source 320 is found to produce a series of spectral lines that extend over the red and IR wavelengths used in oximetry and thus serve to calibrate the device for the required measurements.
  • Sensor calibration involves placing the patient end of the sensor 100 containing the LEDs and photodiode on a light guide 330 which extends from within the monitor 300. The spectra from the LEDs are fed via the light guide to the wavelength sensitive device 310 within the monitor 300.
  • the calculation of the deviation in SATs value is determined as follows with reference to figure 5. 4) The calculation of the deviation in the SATs value is determined using for example a spectrally sensitive pulse oximeter monitor intended for use with a sensor emitting 660nm and 945nm.
  • R-curve b would be appropriate.
  • the R-value generated by the second sensor of wavelengths 665nm and 945nm is read of the x-axis at 4.
  • the error introduced into the pulse oximetry system by a sensor having the incorrect wavelengths can be predicted at any level of oxygen saturation in the patient by calculating the R-curve or looking up previously stored data for the erroneous sensor, and comparing that R-curve with the expected or perfect R-curve.
  • the improvement of the detection system compared with known systems rests in the fact that the calibration process involves the identification of the sensor type by using optical means.
  • a further stage which may be optional, is that after the sensor 100 has been calibrated and the calibration data adjusted for bias introduced by sensor type the calibration data is stored on the micro-controller in the sensor or in the monitor.
  • Any bias introduced by patient parameters is initially set to a default of zero.
  • the user has the choice of selecting patient parameters. These may be selected manually and or automatically from for example in vitro or in vivo blood analysis. The manual selection may be informed from clinical data and or from results of analysis available to the user. Any bias introduced by patient parameters is applied to the results obtained.
  • the sensor is then removed from the light guide 330 ( Figure 1) and placed on the patient (most common site is the finger) and used to obtain data to enable the calculation of the SATs values.
  • the wavelength sensitive device 310 is calibrated using the spectral lines of a Neon-Argon (Ne-Ar) light source 320.
  • the Ne-Ar source 320 is found to produce a series of spectral lines that extend over the red and IR wavelengths used in pulse oximetry and these serve to calibrate the device for the required measurements.
  • the calibration involves placing the patient end of the sensor 100 containing the LEDs and photodiode on a light guide 330 which extends from within the monitor 300.
  • the spectra from the LEDs (not shown) are fed via the light guide to the wavelength sensitive device 310 within the monitor 300.
  • the data to enable this prediction is obtained by doing breathe down trials with various sensor types with hypoxic volunteers representing various patient parameters and collecting data on the amplitude of the pulsatile absorption peak for levels of oxygenation between 100% and 70%, for wavelengths in the range of interest.
  • the R- value can be predicted at various oxygenation values and then it becomes possible to re-construct the R-curve. Examples of the peaks can be seen in our co-pending PCT application (publication WO2008/035076). 9)
  • a suitable light source such as tungsten and/or halogen capable of producing radiation over a wavelength range between, for example 550nm and llOOnm, is set up with a spectrometer that can sample the wavelength range at approximately 200 times/second.
  • each volunteer is desaturated by means of breathing various air/oxygen percentages.
  • the SATs levels are typically monitored by use of a CO-oximeter.
  • the amplitude of the pulsatile component of the heartbeat can be determined for various SATs levels, over the spectral range and any variation in the size of the pulsatile component 200 due to variations in the optics can be removed by normalising the signal.
  • the pulsatile light intensity will vary with wavelength. Also, between data sets, the pulsatile light intensity for a specific wavelength will vary dependant on the amount of tissue perfusion and other biological and other parameters.
  • the R-curve for that particular combination of wavelengths, and indeed for any other combination of wavelengths within the experimental spectral bandwidth, and for any combination of sensor type and patient parameter can be calculated using the tabulated absorption data.
  • the monitor contains a micro-controller details of sensor type are sent to the monitor by optical means.
  • the bias introduced by sensor type is allowed for by selecting a breathe down data set done with that type of senor.
  • the specific calibration data for the specific sensor spectral properties and sensor type are stored in the micro-controller in the sensor.
  • Bias introduced by patient parameters is initially set to a default of zero.
  • the user has a choice of selecting patient parameters. These may be selected manually and or automatically from for example in vitro or in vivo blood analysis. The manual selection may be informed from clinical data and or from results of analysis available to the user. Breathe down data collected for that sensor type and those patient parameters are selected.
  • the R curve is effectively constructed for a specific patient and sensor combination in which spectral properties of the LED's and also specific individual patient parameters are taken into account. It will however be appreciated that the patient parameters can be taken into account irrespective of correction for (or R curve calculation) taking into account spectral considerations of the LED's.
  • the monitor may have one or more manual inputs relating to patient specific parameters. Such inputs could relate for example to patient sex, patient age, patient colour (melanin). These inputs would cause the processor to either apply a correction factor, or be taken into consideration in R curve construction. Typically data relating to R curves for the various parameters selected in this way would be stored (for example in a memory look up table or databank, which may be in the monitor or remote from the monitor but in data communication). Such data will typically be taken from breathe down trials conducted with a relevant sample population exhibiting the relevant patient parameter.
  • the patient specific parameter or parameters may be measured or monitored, and an input into the monitor used to either apply a correction factor, or be taken into consideration in R curve construction.
  • a table of exemplary patient parameters is given below. For each it is identified what the parameter is, the method by which the determination is made and the input method into the monitor for use in the calibration determination.
  • S values - S value is the value for e.g. red or infra red that is used for R/IR calculation to get the Rvalue that is looked up on the Rcurve.
  • the processor in the monitor is preferably used to derive an output for Total oxygen concentration. In order to achieve this it is necessary to determine Hb concentration for input into the formula:
  • the Hb in the calculation is functional Hb - so does not include MetHb or COHb for example.
  • the result could be entered manually or by an communication link between the blood test machine and the monitor.
  • the blood test could be a 'full blood count' or 'blood gas' analysis.
  • the partial pressure of 02 may be adjusted if the patient is receiving hyperbaric oxygen therapy — otherwise a standard value would be used for 'normal atmospheric' levels of oxygen.
  • Oxygen concentration O2 in solution + O2 carried by haemoglobin
  • PaO2 - Partial pressure of oxygen in artery considered to be 0.0225ml oxygen dissolved per 100ml plasma per kPa, or 0.003ml per mmHg
  • R-curves for combinations of red and IR wavelengths can be calculated from blood absorption data at various levels of oxygen saturation. This data is obtained by measuring light absorption of lysed blood samples containing known proportions of haemoglobin, and oxyhaemoglobin. R-curves for the purpose of quantifying the effect of errors in the red and IR spectra are calculated first for the red and then for the IR.
  • R-curves showing the effect of wavelength errors for the red wavelengths can be calculated by varying the red wavelength and keeping the IR constant.
  • the R-curves for 650nm, 655nm and 670nm wavelengths can be calculated using the data for these wavelengths and a constant IR wavelength ( Figure 5).
  • R-curves showing the effect of wavelength errors in the IR can also be calculated.
  • Various R-curves for values in the IR are calculated by using the appropriate data (molar extinction coefficients) for these wavelengths, while assuming a constant value for the red wavelength such as 660nm.
  • R-values can be determined, tabulated and stored within the system 350 for various combinations of red and IR wavelengths.
  • different R-values for different patient parameters can be determined, tabulated and stored within the system.
  • the effect of different patient parameters on the R- curve values could be determined, tabulated and stored and applied to the selected R- values for the various combinations of red and IR wavelengths.
  • the deviation in the SATs value displayed by the monitor, resulting from the deviation in the observed spectra, emitted by the LEDs and the expected spectra from the LEDs, and patient parameters is calculated from knowledge of the wavelength error and can be used to calibrate the monitor and minimise any discrepancies in readings of SATs and or total oxygen concentration.
  • a benefit of the present invention is that it can be used with known devices such as the Lightman pulse oximeter sensor tester.
  • the identification and recognition of optical characteristics associated with the light emitters can be used as a means of identifying and recognising authorised sensors and this has the benefit of reducing the risks to patients by preventing unknowing use of unauthorised sensors.
  • By providing new types of sensors either with one or more dedicated light emitters that produce optical characteristics that can be used for recognising a sensor, or by using a microcontroller in a new type sensor to generate an optical signal which can be recognised by an optical signal. If a known sensor produces an unique optical signal, then this unique signal can be used to identify that sensor.
  • Another beneficial application of the current invention is that it provides the ability to make a calculation of the oxygen content of the blood from knowledge of patient parameters such as the haemoglobin content and oxygen saturation providing the user with additional useful information concerning the oxygen available to the tissue of the patient.
  • the accuracy and reliability of this information will be further enhanced by the increased accuracy of pulse oximetry obtained using one of the described techniques and or methods.
  • the new method of measuring pulse oximetry measurements using R curve calibrations can be used to link the oxygen saturation detected in the blood using pulse oximetry and the amount of haemoglobin in the patient to give an accurate and reliable measurement of the total concentration of oxygen in a patient's blood.
  • optical recognition to provide a knowledge of the sensor type and the intended site of application on the patient allows more specific calibration of R curve data to be used, and further improves the accuracy of pulse oximetry, meaning that the present invention has distinct advantages over known devices used in the field of pulse oximetry.
  • the opaque finger 330 that is used to deliver light from the sensor 100 to the wavelength sensitive device 310 could be replaced by an optical fibre.
  • Optical fibre could be used to deliver the light from the led in the sensor directly to the wavelength sensitive device 310 in order to conduct the spectral analysis to en able creation of the R curve (or application of the necessary correction factor).
  • the photodiode in the sensor could be replaced by an optical fibre leading to a photodiode carried onboard the monitor, or alternatively delivering the light directly to the wavelength sensitive device, 310 which is able to act to derive the required output.
  • the light source may be an Infra Red and red LED sources positioned onboard the monitor.
  • the LED sources may be replaced with a broad spectrum emitter having components in the infra red and red and the light passing via the patient may be directed by optical fibre directly into the wavelength sensitive device 310.
  • the wavelength sensitive device 310 may therefore conduct the spectral analysis of the light and also the measurement of absorption to enable the blood oxygenation to be determined.
  • light data may be fed into the monitor, typically by fibre optics, enabling direct measurement of patient characteristics, for example melanin.
  • absorption of certain wavelengths may be measured by the wavelength sensitive device 310, in order to provide a colourimetric determination of melanin.
  • the light may for example be collected by the end of an optical fibre present in the sensor 100.
  • patient parameter data may be supplied from other patient monitoring means 370 to input into the processor 350.
  • the patient monitoring means 370 may provide input relating to measurement of for example melanin, Carboxyhaemoglobin, Met Hb, sickle cell, foetal Hb, haematocrit.

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Abstract

L'invention concerne un système de surveillance de l'oxygène dans le sang, lequel système a un processeur pour traiter une entrée provenant d'un dispositif de détecteur de lumière. Le processeur reçoit une entrée concernant un ou plusieurs paramètres spécifiques de patient et détermine une sortie sur la base de l'entrée du dispositif de détecteur de lumière et de l'entrée de paramètre spécifique de patient. L'entrée de paramètre de patient est utilisée pour modifier la sortie de système pour assurer une détermination plus précise de la saturation en oxygène. Le système peut être utilisé pour déduire des courbes R spécifiques du patient ou un facteur d'ajustement devant être appliqué à des donnés stockées existantes.
PCT/GB2008/001898 2007-06-06 2008-06-04 Système d'oxymétrie de pouls WO2008149081A2 (fr)

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GB0710885A GB0710885D0 (en) 2007-06-06 2007-06-06 Sensor recognition in the field of pulse oximetry

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US11642037B2 (en) 2008-07-03 2023-05-09 Masimo Corporation User-worn device for noninvasively measuring a physiological parameter of a user
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US12023139B1 (en) 2024-03-07 2024-07-02 Masimo Corporation User-worn device for noninvasively measuring a physiological parameter of a user

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