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Oximeter: Lost SpO2 - and Pulse Values in a Recording

This article applies to the Nox T3 classic and the Nox T3s device connected to the classic Nonin 3150 oximeter and the Nonin 3150 BLE oximeter respectively.


If you have a recording where the SpO2 and Pulse traces are missing, start by verifying if it is because of a lost Bluetooth® radio connection between the Nox T3 and the Nonin 3150. That can be done in Noxturnal.

Typically, a recording with lost SpO2 and Pulse values looks like this on the Recording Results overview page when downloaded in Noxturnal: 

As can be seen in the figure above, data is missing (see encircled area) in the Desaturation and Pulse Signals.

In order to find out if this is the result of a lost Bluetooth radio signal or because of the oximeter probe, move to the respiratory sheet in Noxturnal: 

The red line shows that the oximeter is still connected but no data is streaming from the oximeter to the Nox T3. This is an indication of a damaged oximeter probe or a probe that has fallen off the finger of the patient. 

If you then scale the signal you can see the values 127 and 511 appearing in the SpO2 and Pulse traces: 

These are the default readings the oximeter will send to the Nox T3 if the real SpO2 and Pulse values are missing because of a damaged probe, or the probe has fallen off the finger of the patient. 

For this recording, the reason for lost SpO2 and Pulse values is therefore not a Bluetooth radio disconnection but rather the oximeter probe. Note that the whole recording should be reviewed in order to verify this. 

If however, the gaps seen in the Recording Results page appear as well in the respiratory sheet for the SpO2 and Pulse traces (no red line), then there has been a Bluetooth radio disconnection. It is important that in the configuration phase, the instructions on how to pair the Nox T3 and the oximeter are followed carefully - see instructions here and video tutorial instructions here. 


Additionally, the classic Nonin 3150 oximeter is set to spot-check mode which means that if the probe is disconnected from the oximeter during the recording, the oximeter will automatically turn off. If the probe is then connected again, the oximeter will turn on. If the probe connector is loose, the probe can easily disconnect from the oximeter, and then the oximeter will turn off. This would result in a gap in the oximeter signal in Noxturnal.

The Nonin 3150 BLE oximeter is set to Bluetooth activation mode which means that it will stay on as long as it detects a Bluetooth signal.


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*Please note that not all features or all products are available in all markets. Our products are medical devices and subject to registration/approval in each market area. For more information on product availability please contact

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