AU2008201110A1 - Oximeter sensor with digital memory encoding patient data - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Nellcor Puritan Bennett Incorporated Actual Inventor(s): David Swedlow, Michael E Fein, Paul D Mannheimer Address for Service and Correspondence: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: OXIMETER SENSOR WITH DIGITAL MEMORY ENCODING PATIENT DATA Our Ref: 824553 POF Code: 486120/237528 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- 60004 00 OXIMETER SENSOR WITH DIGITAL MEMORY ENCODING PATIENT DATA tc-I [01] The present application is a divisional application from Australian patent application no. 2005203185, which is a divisional of Australian Patent No.

2001286939, the entire disclosure of which is incorporated herein by reference.

[Ol1a] This application claims priority to U.S. Provisional Patent Application No. 60/229,616, filed August 31, 2001, which is hereby incorporated by reference herein.

c 10 BACKGROUND OF THE INVENTION 00 [02] The present invention relates to oximetry sensors and, in particular, pulse oximetry sensors which include coded information relating to patients.

[03] Pulse oximetry is typically used to measure various blood flow characteristics including, but not limited to, the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and the rate of blood pulsations corresponding to each heartbeat of a patient. Measurement of these characteristics has been accomplished by use ofa non-invasive sensor which passes light through a portion of the patient's tissue where blood perfuses the tissue, and photoelectrically senses the absorption of light in such tissue. The amount of light absorbed is then used to calculate the amount of blood constituent being measured.

[04] The light passed through the tissue is selected to be of one or more wavelengths that are absorbed by the blood in an amount representative of the amount of the blood constituent present in the blood. The amount of transmitted light passed through the tissue will vary in accordance with the changing amount of blood constituent in the tissue and the related light absorption. For measuring blood oxygen level, such sensors have been provided with light sources and photodetectors that are adapted to operate at two different wavelengths, in accordance with known techniques for measuring blood oxygen saturation.

An encoding mechanism is shown in U.S. Patent No. 4,700,708, the disclosure of which is incorporated herein by reference. This mechanism relates to an optical oximeter probe which uses a pair of light emitting diodes (LEDs) to direct light through blood-perfused tissue, with a detector picking up light which has not been absorbed by the tissue. The operation depends upon knowing the wavelength of the LEDs. Since the wavelength of LEDs can vary, a coding resistor is placed in the probe with the value of the resistor corresponding to the actual wavelength of at least one of the LEDs. When the W WM3SpeOP Nof2O20318-8.3.08.dOC 00 oximeter instrument is turned on, it first applies a current to the coding resistor and measures thevoltage to determine the value of the resistor and thus the value of the wavelength of the LED in the probe.

1061 U.S. Patent 5,259,381 recognizes that the coded value of the wavelength of the red LED provided by a coding resistor may be inaccurate, since the actual wavelength can vary with temperature. Accordingly, this patent teaches including a temperature sensor in the oximeter probe to measure the actual temperature. With the actual temperature, and the coded wavelength value, a look-up table can be ccontllted to determine the actual LED wavelength for that temperature.

00 10 [071 Another method of storing coded information regarding the characteristics of the LEDs is shown in U.S. Patent No. 4,942,877 assigned to Minolta. This patent discloses using an EPROM memory to store digital information, which can be provided in parallel or serially from the sensor probe to the remote oximeter. The memory is described as storing coefficients for the saturation equation, wavelength, subwavelength (where 2 peaks for LED), half-width of wavelength spectrum emitted by LED, intensity of LEDS or ratio, and on time of L;EDS (written by the processor).

[08] Other examples of coding probe characteristics exist in other areas.

Multiple calibration values are sometimes required, with this making the circuitry more complex or requiring many leads. In Patent No. 4,446,715, assigned to Camino Laboratories, Inc., a number of resistors are used to provide coded information regarding the characteristics of a prestsure transducer. Patent No. 3,790,9 10 discloses another pressure transducer with a ROM storing characteristics of thle individual transducer. Patent No. 4,303,984 shows' another probe with digital characterization information stored in a PROM, which is read serially using a shift register.

[09] Typically, the coding element is mounted in the probe itself For instance, U.S. Patent No. 4,621,643 shows the coding resistor mounted in the probe element itself In addition, U.S. Patent No. 5,246,003 shows the coding resistor being formed with a printed conductive material on the probe itself [101 In some devices, an electrical connector coupled by a cable to a device attached to a patient may include a coding element For eiample, U.S. Patent No. 3,720,199 shows an intra-aortic balloon catheter with a connector between the catheter and a console.

The connector includes a resistor with a value chosen to reflect the volumetric displacement of the particular balloon. U.S. Patent No. 4,684,245 discloses a fiberoptic catheter with a module between the fiberoptic and electrical wires. connected to a processor. The module 00 converts the light signals into electrical signals, and includes a memory storing calibration Ssignals so the module and catheter can be disconnected from the processor and used with a different processor without requiring a recalibration.

S[11] Patent No. 5,645,059 teaches using a modulated signal to provide the coded data to a remote analyzer. Patent No. 5,429,129 shows using a voltage regulator to produce a specific voltage value in response to an attempt to read by the analyzer.

[12] Hewlett-Packard Company Patent No. 5,058,588 teaches an oximeter sensor with an encoding element that could be resistor, ROM, or customized integrated circuit The encoding element encodes the type of sensor (in particular, type indicating area 0C 10 of placement on body finger, ear, foot, arm; also, the type of sensor can indicate transmission/reflection type, or adult/neonate {indicating correction to be performed on theoretical oxygen saturation, allow switching between physiological limits such as minimum/maximum pulse rates for adults/neonates}; the maximum driving current may be adapted according to type of sensor, and contact of sensor with tissue can be tested by means of an attenuation measurement if sensor type is known).

[13] Nellcor Patent No. 5,645,059, the disclosure of which is hereby incorporated herein by reference, teaches coding information in sensor memory used to provide pulse modulated signal, to indicate the type of sensor (finger, nose), the wavelength of a second LED, the number of LEDs, the numerical correction terms to the standard curves, and an identifier of the manufacturer.

[14] A number of catheter patents also discuss encoding information in the catheter. Sentron Patent No. 4,858,615 teaches encoding the type of sensor, type number, serial number, date ofproduction, safe use life of the sensor, correction data for non-linearity, pressure sensitivity, offset, and temperature sensitivity.

[15] Interflo Medical Published PCT Application No. PCT/US92/08263, Publication No. WO 93/06776 teaches encoding patient specific data, size, manufacture date, batch number, sterilization date, expiration date, transducer number and type, manufacturer's name and address, thermistor heating element resistance, filament efficiency, program segments or patient historical'data., format version for the calibration data, trademark information, catheter unique serial number, ship date, other date and time information, security code to identify manufacturer, thermal mass, filament composition, coefficient of resistance, layout byte, checksum, copyright, number of seconds since a certain date, patient weight, patient height, timestamp of 1st CO data point, and a count of all CO data points in

EEPROM.

00 [16] Dulex-Ohmeda of Boulder, Colorado markets an oximeter sensor Sproduct that encodes data into resistor values representing pointers to a lookup table containing coefficients (as in U.S. Patent No. 4,700,708) as well as indicating a range of SLED drive current to use with the sensor. The LEDs are driven with a higher or lower drive currents depending upon the value of the resistor in a particular sensor.

S[17] Honeywell Patent No. 4,303,984 (expires 12-14-99) describes a memory which stores characterization information, such as linearization information for a pressure sensor. Alnor Instrument Patent No. 5,162,725 describes storing both calibration and ID information in a sensor memory. Seimans Patent No. 5,016,198 describes a coding CI 10 memory in a sensor with data for defining sensor's characteristic curve. McBean Patent No.

00 5,365,462 describes a date code in a sensor memory. Honeywell Patent No. 4,734,873 CI describes a pressure sensor with a PROM storing coefficients for a polynomial. Robert Bosch Patent No. 4,845,649 describes a PROM in a sensor storing correcting data.

[18] McBean Patent No. 5,371,128 relates to EEPROM in sensor with sensor type code and calibration data. McBean Patent No. 5,347,476 describes an accuracy code. Otax Patent No. 5,528,519 shows a PROM in a connector for oximeter.

[19] Square D Company Patent No. 5,070,732 shows calibration data in a sensor memory. Baxter Patent No. 5,720,293 talks about different calibration information for a catheter, including a security code (encryption is discussed), serial number, model number, ID data such as calibration, manufacture, sterilization and ship date or other date and time information, a software program segment, security code for identifying whether sensor made by same manufacturer as monitor manufacturer, filament or transducer resistance, heat transfer coefficient, thermal mass, filament composition and coefficient of resistance, layout byte, copyright notice, checksum, random data bytes. Porsche Patent No.

5,008,843 describes a sensor with EEPROM ID and characteristics data.

[19a] The discussion of the background to the invention is included herein to explain the context of the invention. It is not to be taken as an admission or a suggestion that any of the material referred to was published, known or part of the common general knowledge as at the priority date of any of the claims.

BRIEF SUMMARY OF THE INVENTION In its various embodiments, the present invention provides a memory chip for use in an oximeter sensor, or an associated adapter or connector circuit.

The memory chip allows the storing of patient related data, such as patient trending data or a patient ID, to provide enhanced capabilities for the oximeter sensor. In addition to 00 providing unique data to store in such a memory, the present invention includes unique uses of the data stored in such a memory.

In one aspect, the present invention provides an oximeter sensor Sincluding a light emitting element, a light detecting element and a memory device for storing digital data. Said digital data includes a patient identification code.

In another aspect, the present invention provides an oximeter sensor including a light emitting element, a light detecting element and a memory device for storing digital data. Said digital data includes a length of time that a patient has been monitored using the oximeter sensor.

C 10 [20c] In another aspect, the present invention provides an oximeter sensor 00 Sincluding a light emitting element, a light detecting element and a memory device for C storing digital data. Said digital data includes a time when an oximeter monitor coupled to the oximeter sensor was turned on or turned off.

In yet another aspect, the present invention provides an oximeter sensor including a light emitting element, a light detecting element and a memory device for storing digital data. Said digital data includes oximeter alarm limit values that are patientspecific.

In another of its aspects, the present invention provides a method for storing data in an oximeter sensor. The method includes the steps of emitting light from a light emitting element, detecting light from the light emitting element using a photodetector and storing digitally encoded data in a memory in the sensor. The digitally encoded data includes a patient ID and tracking patient information using the patient ID.

In another aspect, the present invention provides a method for storing data in an oximeter sensor. The method includes the steps of emitting light from a light emitting element, detecting light from the light emitting element using a photodetector and storing digitally encoded data in a memory in the sensor. The digitally encoded data includes a time when an oximeter monitor coupled to the oximeter sensor was turned on or turned off in the memory.

In another aspect still, the present invention provides a method for storing data in an oximeter sensor. The method includes the steps of emitting light from a light emitting element, detecting light from the light emitting element using a photodetector and storing digitally encoded data in a memory in the sensor. The digitally encoded data includes a duration of time that a patient has been monitored using said oximeter sensor.

00 BRIEF DESCRIPTION OF THIE DRAWINGS [21] FIG. 1 is a block diagram of a pulse oximeter system in accordance with an embodiment of the present invention.

~DETAILED DESCRIPTION OF THE INVENTION' [221 FIG. I is a block diagram of a pulse oximeter system incorporating a calibration memory element 56 according to the invention. In one embodiment, memory element 56 is a two-lead semiconductor digital memory chip. The calibrfifon element is part of the sensor 50 -which also includes red and infrared LEDs 52 as in the prior art, along with a ci 10 detector 54. If desired, LEDs 52 may be replaced with other light emitting elements such as 00 lasers.

[231 The oximeter includes read circuit 60, drive circuit 66, look-up tables 62 and 63, controller 64, amplifier 72, filter 74, and analog-to-digital converter 76. Read circuit 60 is provided for reading multiple coded values across the two leads 51, 53 connected to calibration element 56. One value is provided to a look-up table 62 to determine appropriate wavelength dependent coefficients for the oxygen saturation calculation, as in the prior art. The other value(s) are then provided to another look up table(s) 63 which provides input coefficients) to other calculations performed by controller 64. These additional calculations may enhance the performance and/or safety of the system. Controller 64 provides signals to a drive circuit 66, to control the amount of drive current provided to LEDs 52.

(241 As in the prior art, detector 54 is connected through an amplifier 72 and afilter 74to an ADconverter 76. This forms a feedback path used by controller 64 to adjust the drive current to optimize the intensity range of the signal recived. For proper operation the signal must be within the analog range of the circuits employed. The sigil should also be well within the range of AID converter 76. For example, one rule that may be applied is to adjust LED drives and amplifier gains so that both red and IR signals fall between 40% and 80% of fulfl scale reading of converter 76. This requires correct and independent settings for both the red and infrared LEDs..

[251 In an embodiment of the present invention, patient-specific data such as trending data or patient monitoring parameters can be actively stored in the memory of memory chip 56. As the patient and sensor travel from ward-to-ward of the hospital, and consequently plug into different oximeters, the patient-specific data can be read from memory 56 of the patient's dedicated sensor and displayed on a display screen for viewing or 00 used by the oximeter monitor for other purposes. Memory 56 may, for example, be 0 implemented as a random access memory (RAM), a FLASH memory, a programmable read N only memory (PROM), an electrically erasable PROM, a similar programmable and/or erasable memory, any kind of erasable memory, a write once memory, or other memory technologies capable of write operations. Examples of patient specific data that can be stored in memory 56 are now discussed.

[261 Patient trending data regarding the history of a patient's blood oxygen saturation (SpO 2 level, pulse rate, pulse amplitude, perfusion data, and biher patient data over a period of time can be recorded in memory chip 56. The oximeter monitor can 00 10 continuously or periodically store a patient's current trend data into memory 56 to maintain a historical data for the patient The patient trend data can be erased from memory 56 each time a sensor is used on a new patient each time the oximeter monitor is turned off or when user input to the monitor indicates a new patient). Alternatively, the data encoded into memory 56 can be permanent and non-erasable. Further details of a Method and Circuit for Storing and Providing Hfistorical Physiological Data are discussed in U.S. Patent Application No. 09/520,104 to Swedlow et al., filed March 7, 2000, which is incorporated by reference herein in its entirety.

[271 As another example, the lowest and/or highest blood oxygen saturation level, pulse rate, pulse amplitude value, temperature data, blood pressure, perfusion data, or any other patient data during the monitored time may be stored in memory 56 by the oximeter monitor. If desired, the lowest/highest values of these patient parameters over a past speified monitoring time 2 hours, I day, etc.) may be recorded in memory 56.

[28] Expected ranges for patient parameters (such as pulse rate, pulse amplitude, and blood oxygen saturation level) that are specific to a particular patient may also be recorded in memory 56 by aclinician. This can be a desirable feature, because the expected patient trending data can vary significantly for each patient The oximeter monitor can compare the expected range for the patient stored in memory 56 with the monitored patient trending data to determine if the patient's pulse and blood oxygen levels are withn the expected range for that patient If the monitored patient parameter varies outside the patient-specific range recorded in memory 56, a warning message may be displayed on the oximeter monitor or alarmn signal may be sounded. If desired, any variations in the monitored patient parameters from the expected ranges may be recorded in memory 56 along with a time stamp.

00 [29] If desired, poitions of a patient's medical chart and/or past medical history can'be digitally encoded and stored in memory 56 (if sufficient memory space is available) so that this information is maintained with the patient as he is moved around and can be easily accessed and displayed using an oximeter monitor if the patient transferred to a different room or hospital.

The pulse oximeter can keep track of how long a particular patient has been monitored by the pulse oximeter and can periodically store that time interval in memory 56 by checking the elapsed time on a counter. The counter may be a circuit element in the 0oxineter monitor that is reset each time the oximeter monitor begins to receive data signals from a sensor or each time that the oximeter monitor is turned off. The time period that a patient has been monitored by the oximeter sensor may be displayed on a display screen for viewing.

(311 The pulse oximeter monitor may also include a digital clock that keeps track of the current date and time. The date and time that the oximeter monitor was turned on and the date and time that the oximeter monitor was turned off may be encoded into the sensor in memory 56. When the oximeter monitor is turned back on again, the monitor can display the date and time that it was last turned on and off. It may be desirable for medical personnel to know the last time that patient's vital signs were monitored by the oximeter.

[321 The oximeter monitor instrument may also write the alarm limits used with a particular patient into memory chip 56. Alarm limits are values that represent maximum or minimum values of patient trending data tracked by the oximeter (such as blood oxygen saturation, pulse rate, pulse amplitude, etc.) that will trigger an alarm, because they are considered to be dangerous levels. The alarm limit values may be encoded in memory 56 by the manufacturer or by a clinician through the oximeter monitor prior to operation.

[33] The oximeter monitor periodically checks the patient's monitored trending data against the alarm limit values. When one of the monitored patient parameters reaches the alarm limit value stored in memory 56, the oximeter monitor triggers an alarm which alerts medical personnel that a problem may exist The present invention also allows patient-specific alarm values to be set by medical personnel through the oximeter and stored in memory 56 so that as the patient moves from monitor-to-monitor (while the sensor stays with the patient), the appropriate alarm limits need not be reset each time on the new monitor.

Instead, the alarm limits only need to be programmed once, or at a later time, whenever the clinician adjusts alarm limits.

00 [341 One of more of the patient trending data including blood oxygen saturation, pulse rate, and pulse amplitude can be written to memory 56 along with a time of occurrence whenever an alarm threshold is crossed. Additional information, such as the readings for a predetermined time prior to an alarm occurrence can also be stored, and/or periodic values during the alarm breach can also be stored in memory 56.

Currently sensors are placed on patients at one hospital site and stay with the patient from hospital site-to-site. It would therefore be desirable to have a patient identification code (patient ID) such as a unique number carried along in the-sensor so that the record keeping, which occurs at each site, can link the recorded information with the N 10 patient Without a patient ED) stored in the sensor itscW the tracking has to be done manually.

This method is prone to mistakes and increases the labor involved in managing the patient Thus, in a further embodiment of the present invention the oximeter monitor can store a patient ID) in memory 56 of sensor 50. The oximeter has an input device such as a keyboard, touch screen, or scanner that allows a patient ID to be entered and reentered into the oximeter so that it can be stored in sensor memory 56. With patient trending information being stored in memory 56 of the sensor as discussed above, it is also desirable to have the patient ID stored in memory 56 so that as the patient goes from hospital location to location, the new location's staff an. verify that old trending information stored in memory 56 was indeed obtained from that particular patient Medical personnel can check that the patient ID) stored in sensor 50 matches the patient ID on the patient's chart and other paper documentation to verify that these medical records correspond to the correct patient If desired, the oximeter sensor can be interfaced with a hospital computer network that maintains a database of patient ED numbers to verify the identify of the patient and to obtain medical records and other information for the patient stored on hospital. databases. The.

patient ID stored in memory 56 provides assurance that any data read from memory 56 of the sensor is correlated with the patient they are receiving..

[371 The pulse amplitude of the measured photoplethysmogram is an indirect measure of blood perfusion (flow) in the local tissue, changes in blood pressure, vascular tone, vasoconstriction or dilation, for example, all have an effect on the pulsatile signal strength observed with a pulse oximeter.

(381 The measured modulation, or other measurement of perfusion, can be stored in memory 56 for patient trending purposes. The oximeter can compare current modulation and perfusion data with older data from memory 56 to determine patient trends over time. The patient's pulse amplitude deteriorating over time may reflect a serious o condition that demands attention. Therefore, it is desirable to store and monitor changes in a Spatient's perfusion over time. Also, a maximum or minimum perfusion limit may be stored in memory 56 that represents the maximum or minimum value that the patient's measured Sperfusion can reach before the sensor needs to be moved, repositioned, or adjusted in some other way. The oximeter can trigger a warning signal or light when a perfusion limit has O been reached or a significant change has occurred.

[39] While the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and Ssubstitutions are intended in the foregoing disclosure, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of Sother features without departing from the scope of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope and spirit of the present invention.

It is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments and equivalents falling within the scope of the claims.

Claims (12)

1. An oximeter sensor including: Sa light emitting element; a light detecting element; and a memory device for storing digital data, said digital data including a patient identification code.

2. An oximeter sensor including: 00 10 a light emitting element; O a light detecting element; and a memory device for storing digital data, said digital data including a length of time that a patient has been monitored using the oximeter sensor.

3. An oximeter sensor including: a light emitting element; a light detecting element; and a memory device for storing digital data, said digital data including a time when an oximeter monitor coupled to the oximeter sensor was turned on or turned off.

4. An oximeter sensor including: a light emitting element; a light detecting element; and a memory device for storing digital data, said digital data including oximeter alarm limit values that are patient-specific. The oximeter sensor of claim 4 wherein the alarm limit is a maximum or minimum blood oxygen saturation level.

6. The oximeter sensor of claim 4 wherein the alarm limit is a maximum or minimum pulse rate. 00 7. The oximeter sensor of any one of claims 4 to 6 wherein said memory device 0 Sencodes patient trending data after an alarm limit value has been reached.

8. The oximeter sensor of claim 7 wherein said patient trending data includes perfusion data.

9. The oximeter sensor of claim 7 or claim 8 wherein said patient trending data includes blood oxygen saturation levels. 00 10 10. The oximeter sensor of any one of claims 4 to 9 wherein said memory device Sencodes a patient trending data periodically before an alarm limit value has been reached.

11. The oximeter sensor of any one of claims 7 to 10 wherein said patient trending data includes blood oxygen saturation levels.

12. The oximeter sensor of any one of claims 7 to 11 wherein said patient trending data includes blood perfusion data.

13. The oximeter sensor of any one of claims 4 to 12 wherein said memory device encodes a time that an alarm limit was initially breached.

14. A method for storing data in an oximeter sensor, the method including the steps of: emitting light from a light emitting element; detecting light from the light emitting element using a photodetector; and storing digitally encoded data in a memory in the sensor, the digitally encoded data including a patient ID; and tracking patient information using the patient ID. A method for storing data in an oximeter sensor, the method including the steps of: emitting light from a light emitting element; 00 detecting light from the light emitting element using a photodetector; and O N storing digitally encoded data in a memory in the sensor, the digitally encoded data including a time when an oximeter monitor coupled to the oximeter sensor was Sturned on or turned off in the memory.

16. A method for storing data in an oximeter sensor, the method including the steps of: emitting light from a light emitting element; Sdetecting light from the light emitting element using a photodetector; and 00 10 storing digitally encoded data in a memory in the sensor, the digitally encoded Sdata including a duration of time that a patient has been monitored using said oximeter sensor.