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  • Writer's pictureArun Bhatia

How does the pulse oximeter work?

How does the pulse oximeter work?

• The pulse oximeter works out the oxygen saturation by shining light

through your finger. The sensors detect how much oxygen is in your

blood by comparing how much red light and infra-red light is

absorbed by the blood. Depending on the amounts of oxygenated Hb

and deoxygenated Hb present, the ratio of the amount of red light

absorbed compared to the amount of infrared light absorbed


Normal values

· Normal pediatric pulse oximetry (SP02) values have not yet been firmly established.

· SPO2 is lower in the immediate newborn period. Beyond this period,

· normal levels are stable with age.

· Generally, a SPO2 of <92% should be a cause of concern and may suggest a respiratory disease or cyanotic heart disease.

· 96-98 is referred to as normal.


· Incorrect reading if the probe falls off the earlobe, toe, or finger.

· Nail polish: it can interfere with the readings, should be removed.

· Anemia

· Hypovolemia, hypotension, and hypothermia: may have adequate

· oxygen saturation, but low oxygen carrying capacity. Due to the

· reduction in blood flow, the sensor may not be able to pick up

· adequately the pulsatile waveform resulting in no signal or loss of

· accuracy.

· Dark skin pigmentation can give over-estimated Sp02 readings when

· it is below 80%.

· Intravenous dyes (such as methylene blue, indigo carmine, and

· indocyanine green) can cause inaccurate readings.

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