SpO₂  Sensors

The SpO₂  value is often affected by the patient’s condition, artifacts created by external devices or by inappropriate attachment of probes. Nihon Kohden’s monitor has several features for better SpO₂  measurement. Let us introduce four features: Signal Quality Index (SQI), Pulse-amplitude Index (PI), Response, and Sensitivity Mode.^

Nihon Kohden’s monitors display the quality of the pulse waveform signal, which is used to measure SpO₂, by a bar graph. If the SQI bar graph displays 2 yellow bars or below, check for the patient’s physical movement and/or how the probe is attached.

SQI Bar Graph	Signal Quality
	Good.
	There may be some artifacts.
	There may be significant artifacts. If this continues for a while, check the patient and probe attachment site.
	Very low. Check the patient and probe attachment site.
	The signal cannot be detected.

The Pulse-amplitude Index, PI, indicates the percentage of the pulsatile signal as a proportion of the entire transmitted infrared signal. It fluctuates depending on the size of transmitted signal and the size of the pulsatile signal obtained from the probe attached to the patient.

PI can be used as an index to confirm the circulation of the attachment site as well as to check the condition of an attachment site of SpO₂ probe so if the attachment site is too thick or if an SpO₂ probe is inappropriately attached, the intensity of the transmitted light decreases, meaning the PI value becomes low. When the PI is low, any of the following situations might be happening.

• Measurement site is cold
• SpO₂ probe is attached too tight
• The patient is in a condition of shock
• The patient is a premature baby

If the PI value is low, check the probe attachment as the probe may block blood flow of the measurement site due to the high pressure if it is attached too tight.
If the PI value is low, but the probe is properly attached, change the probe attachment site for more reliable SpO₂ measurement.
If the SpO₂ value and PI value are dropping simultaneously, there is a possibility that the SpO₂ probe might have deviated from the correct attachment position.

This is a feature that lets you set the response times of the SpO₂;value. We have Normal, Slow and Fast mode.

Normal: Standard response time
Slow: Slower response. This is useful when you want to control transient fluctuations in the SpO₂;value.
Fast: Faster response. This can be used in a situation that requires an extremely fast response.

When measurement condition is unstable such as due to strenuous movement of the patient, response may become slower in all modes.

Sensitivity mode allows you to improve the sensitivity of the pulse wave, therefore this feature is useful when it is difficult to detect the pulse of a patient with peripheral circulation insufficiency or when an IABP (Intra-Aortic Balloon Pump) is used. On the other hand, an SpO₂ value may be measured even if the probe is detached from the patient. Therefore, when selecting “Max” for the setting, it is necessary to confirm that the probe is appropriately attached to the patient.

A pulse oximeter detects the light that penetrates the measurement site. In most cases, a probe should be attached across a measurement site with a thickness of 6-18 mm to obtain stable and accurate SpO₂;value.

To obtain stable and accurate SpO₂ measurement, the probes should be attached in the correct position so that the light emitter and the photo detector face each other like in the following image.

To prevent skin damage due to prolonged attachment, it is important to check and change the attachment site if necessary.

For single-patient use probes: within every 8 hours

For reusable types: within every 4 hours