Pediheart: Pediatric Cardiology Today
Sep 25, 2026 · 25 min · 9 segments
This week we replay an episode from 2022 i which we reviewed a then recent report on the differences between pulse oximeter Sp02 and arterial Sa02. Are there patient specific factors that may result…
Robert PassHost
Cara PritchettGuest
It is, in fact, a research letter on the topic of pulse oximetry error in patients with single ventricle physiology.
As we all know in this field, pulse oximetry is really a modern miracle that was first developed in Japan in 1972, but it took another 15 years before it became the standard of care for the administration of general anesthesia in the United States, and its use rapidly moved from the operating room to the recovery room and then ICUs, where they have basically become the standard of care.
The most common form of pulse ox all use the so-called transmissive pulse ox, in which a sensor device is placed on a thin part of a patient like a fingertip or an earlobe.
The device then passes two wavelengths of light through the body to the photo detector, and the change in absorbance at each of the wavelengths used allows the device to determine the oxygen saturation.
Essentially, the goal of the monitor is to measure what percentage of hemoglobin is loaded with oxygen.
The devices typically have an LED that is red of one wavelength and the others infrared of another wavelength.
The absorption of light of these wavelengths will differ based upon the degree of oxygen bound to hemoglobin.
Oxygenated hemoglobin will absorb more infrared light and allow more red light to pass through, whereas deoxygenated hemoglobin will allow absorption of more red light and allow more infrared light to go through.
These sequences from the LEDs are happening literally 30 times a second and allow the sensor to respond to the red and infrared light separately.
The amount of light that's not absorbed and transmitted is measured and the ratio of red light to infrared light is then calculated and converted to an SpO2.
The clear advantage of these devices is rapid non-invasive estimate of blood oxygen saturation.
We are, however, aware of a few things that can limit the accuracy of these devices or the utility, such as methemoglobinemia, cyanide poisoning, or carbon monoxide poisoning.
Also, erroneous low levels can be caused by low perfusion, calloused skin, obesity, low blood pressure, some hemoglobin variants, to name a few.
Importantly, it's well established that at lower oxygen saturation levels, the accuracy of the SpO2 monitor is slightly less.
It is, in fact, a research letter on the topic of pulse oximetry error in patients with single ventricle physiology.
As we all know in this field, pulse oximetry is really a modern miracle that was first developed in Japan in 1972, but it took another 15 years before it became the standard of care for the administration of general anesthesia in the United States, and its use rapidly moved from the operating room to the recovery room and then ICUs, where they have basically become the standard of care.
The most common form of pulse ox all use the so-called transmissive pulse ox, in which a sensor device is placed on a thin part of a patient like a fingertip or an earlobe.
The device then passes two wavelengths of light through the body to the photo detector, and the change in absorbance at each of the wavelengths used allows the device to determine the oxygen saturation.
Essentially, the goal of the monitor is to measure what percentage of hemoglobin is loaded with oxygen.
The devices typically have an LED that is red of one wavelength and the others infrared of another wavelength.
The absorption of light of these wavelengths will differ based upon the degree of oxygen bound to hemoglobin.
Oxygenated hemoglobin will absorb more infrared light and allow more red light to pass through, whereas deoxygenated hemoglobin will allow absorption of more red light and allow more infrared light to go through.
These sequences from the LEDs are happening literally 30 times a second and allow the sensor to respond to the red and infrared light separately.
The amount of light that's not absorbed and transmitted is measured and the ratio of red light to infrared light is then calculated and converted to an SpO2.
The clear advantage of these devices is rapid non-invasive estimate of blood oxygen saturation.
We are, however, aware of a few things that can limit the accuracy of these devices or the utility, such as methemoglobinemia, cyanide poisoning, or carbon monoxide poisoning.
Also, erroneous low levels can be caused by low perfusion, calloused skin, obesity, low blood pressure, some hemoglobin variants, to name a few.
Importantly, it's well established that at lower oxygen saturation levels, the accuracy of the SpO2 monitor is slightly less.
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