The Importance of Selecting the Appropriate Attachment Site

Brochures and other product information indicate body weight of the patient as a yardstick for the selection of probes. However, because body weight is only a rough yardstick and the pulse oximeter detects the light penetrating the measurement site, it is necessary to base this selection on the thickness of the site at which the probe is attached. In most cases, a probe should be attached across a measurement site with a thickness of 6-18 mm.

Probe attachment on Infants and Neonates

When the probe is attached to a small patient, the recommended site is the big toe (1st toe), where a relatively large amount of the pulse can be detected. If measurement is made across a foot, target at the base of the 4th toe, as shown in the figure above, and place the probe so that the measurement site is sandwiched. This will reduce the effect from the thickness of measurement site as compared with the areas near the big toe, making it easier to detect the pulse.
Besides, sometimes neonates are wrapped in a blanket for their comfort, warmth and security. In that case, the SpO₂ value may be inaccurate or unstable if a probe is attached to their hand when it is placed between the blanket and themselves, as the probe might get unnecessary strong pressure by breathing. In such case, attach a probe to their toe, instep or sole so an accurate and stable value can be measured.

Measurement on the Earlobe

Nihon Kohden provides clip type adapters for SpO₂ measurement in places other than the fingers and toes (to be used with TL-260T). Because the pulses detected with the earlobe are about 10 times as small as those detected in fingers and toes, we recommend measurement on fingers and toes for routine examinations.
However, measurement on the earlobe can be advantageous a) when attaching a probe to a finger or toe is difficult due to any accident or any disease, or b) in cases when pulse is difficult to detect because of the contraction of peripheral blood vessels or low perfusion.^*1
In addition, the use of earlobe probes in combination with telemetry can be effective for the improvement of the quality of life of patients in hospital wards.
  ^{*1 The Japanese Journal of Medical Instrumentation, Vol. 79, No. 8 (2009). “A New Approach to Percutaneous Arterial Oxygen Saturation (SpO₂) Measurement: An Attempt with Earlobe Sensors.”}