In this record we reviewed the digital memory chip residing in the Nellcor OxiMax sensor connectors and related for clarifying our understanding. In the process, we had learned new things together.
Pulse Oximetry sensors is biggest of the four major segments in the patient monitoring supplies market including ECG supplies, capnography supplies and NIBP cuffs.
As said, in this review we explore the digital memory chip residing in the Nellcor OxiMax sensor connector.
Nellcor, among others competes in the SpO2 measurement market. Philips Healthcare, GE Healthcare, Mindray Medical, Draeger Medical, Nihon Kohden Corporation and many others all have OEM arrangements with Covidien Nellcor to allow their patient monitors to make use of Nellcor OxiMax sensors, reflecting the Brand power of Nellcor in the SpO2 measurement market.
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| Image 1: Location of EPROM is in the sensor connector |
The Image 1 above pinpoints the location of a
OxiMax SpO2 sensor connector equipped
with a digital memory chip enclosed in the connector to store calibration data. The calibration data in each connector is unique and belongs to the actual pair of
LEDs employed in the making of the particular finger sensor which is linked to the same connector. Other information like probe type and sensor-dependent operating messages and data for
sending to the monitor are also included. There are also rooms to provide and store additional data type that will help enhance performance of the SpO2 measurement, plus the possibility to change the encryption public key of the calibration data to strengthen measures against use of unauthorized sensors on their SpO2 monitor.
The calibration data is obtained and stored during production of the sensor. Each pair of LEDs in the sensor combined to give different measurement curves and the unique calibration data for the particular sensor will make for more accurate and consistent SpO2 measurements in the field.
The calibration data is obtained and stored during production of the sensor. Each pair of LEDs in the sensor combined to give different measurement curves and the unique calibration data for the particular sensor will make for more accurate and consistent SpO2 measurements in the field.
Most manufacturers only has one default calibration
curve in the SpO2 monitor and will only select those LED pairs during production which fit the reference curve residing in the SpO2 monitor to within certain tight tolerance to ensure accuracy performance.
This traditional arrangement results in more rejections during the manufacturing
process but the OxiMax way has more work to do during production.
We think the main reason Nellcor going for OxiMax is to protect their sensor sales. By adopting OxiMax, Nellcor users are faced with the following doubts if they want to consider alternative suppliers for the sensors.
1. Lower cost sensors without the digital memory will not work on a OxiMax monitor.
2. Even if an alternative supply could equip the sensor with the required memory chip and provide a valid calibration data recognized by the monitor, a user cannot be sure the calibration data contained in the memory is to be trusted and not just some random data.
Any hospital or care facilities will shunt away from buying sensors not originally produced by Nellcor for the said concerns and Nellcor can equate the higher cost with promised performance. OxiMax therefore has the net effect of ensuring
higher sensor sales for Nellcor for a given number of installed units.
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| Image 3: Oximax EPROM chip and the sensor connector |
The calibration data embedded in the
connector also allows for employment of new generation LEDs when they become
available in the future, promising higher energy efficiency or greater intensity providing for improved sensitivity.
Refer to Image 3, The shown EPROM is a different type of non-volatile erasable memory from the EEPROM embedded in the Nihon Kohden Smart Cables. The typical applications for this kind of EPROM include storing of access password, maintenance history, asset tracking or ID code to prevent third-party consumable sales, software revision history etc. You will be surprised that this EPROM can be operated using only two wires, the same number of wires as the previous calibration code using a resistor practiced by Nellcor. This simplicity of operation of the digital memory chip might have been an important point for Nellcor to adopt it.
Translating from typical maintenance history to patient care, this can become the Sensor Event Report (patient history) in the case of a OxiMax SpO2 sensor. The embedded EPROM in the connector is an add-only type allowing additional data to be added in the field without disturbing what has already been by the factory. Contrary to what the EEPROM can do, the Sensor Event Report data in an EPROM cannot be over-written using the same writing method twice and storage is thus limited by this property. This is roughly equivalent to saying EPROM is like CD-R, while EEPROM like CD-RW. The data on the EPROM can only be deleted but not over-written during use though the whole EPROM can be re-cycled using a re-manufacturing process. Thus, only single-patient-use sensor type can be considered to have the facility of storing Sensor Event Report. This does not seem to be a problem in the USA market as more than 90% of the sales are disposable sensors.