Why do we measure oxygen saturation

Arterial oxygenated blood is red due to the quality of oxyhaemoglobin it contains, causing it to absorb light of certain wavelengths. The oximeter probe has two light-emitting diodes LEDs , one red and one infrared, located on one side of the probe. The probe is placed on a suitable part of the body, usually a fingertip or ear lobe, and the LEDs transmit light wavelengths through pulsating arterial blood to a photodetector on the other side of the probe. Infrared light is absorbed by the oxyhaemoglobin; red light by the reduced haemoglobin.

Pulsatile arterial blood during systole causes an influx of oxyhaemoglobin to the tissue, absorbing more infrared light, and allowing less light to reach the photodetector.

The oxygen saturation of the blood determines the degree of light absorption. The result is processed into a digital display of oxygen saturation on the oximeter screen, which is symbolised as SpO2 Jevon, There are various makes and models of pulse oximeters available Lowton, Most provide a visual digital waveform display, an audible display of arterial pulsations and heart rate, and a variety of sensors to accommodate individuals regardless of age, size or weight.

Selection depends on the setting in which it is used. All staff using the pulse oximeter must be aware of its functions and correct usage. Arterial blood gas analysis is more accurate; however, pulse oximetry is considered sufficiently accurate for most clinical purposes, having recognised that there are limitations. Patient condition - To calculate the difference between full and empty capillaries, oximetry measures light absorption over a number of pulses, usually five Harrahill, In order for a pulsatile flow to be detected, there must be sufficient perfusion in the monitored area.

If the patient has a weak or absent peripheral pulse, pulse oximeter readings will not be precise. Patients most at risk of low perfusional states are those with hypotension, hypovolaemia and hypothermia and those in cardiac arrest.

Patients who are cold but not hypothermic may have vasoconstriction in their fingers and toes that may also compromise arterial flow Carroll, Non-arterial pulses may be detected if the probe is secured too tightly, creating venous pulsations in the finger. Venous pulsations are also caused by right-sided heart failure, tricuspid regurgitation Schnapp and Cohen, , and the tourniquet effect of a blood pressure cuff above the probe. Intravenous dyes used in diagnostic and haemodynamic testing may cause inaccurate, usually lower, estimates of oxygen saturations Jenson et al, The effects of deeply pigmented skin, jaundice or bilirubin levels should also be considered.

Using pulse oximetry correctly involves more than just reading the number display, since not all patients with the same SpO2 have the same amount of oxygen in their blood.

Another factor that affects the oximeter readings is how tightly the haemoglobin and oxygen are bound together, which may change with various physiological conditions. External influences - Because the pulse oximeter measures the amount of light transmitted through arterial blood, bright light that shines directly on the sensor, whether artificial or natural, may affect readings.

Dirty sensors Sims, , dark-coloured nail polishes Carroll, and dried blood Woodrow, may affect the accuracy of the readings by hindering or altering the light absorption of the contact probes. Optical shunting affects accuracy and occurs when the sensor is improperly positioned so that light goes directly from the LED to the photodetector without passing through the vascular bed. Moving and dislodging of the sensor, which may be caused by a rhythmic movement such as the tremors of Parkinsonism, seizures or even shivering, may leads to inaccurate readings.

Exercise and vibrations can also make it difficult for the pulse oximeter to determine which tissue is pulsatile. False high readings - Pulse oximeters can give a falsely high reading in the presence of carbon monoxide. Carbon monoxide binds to haemoglobin about times more strongly than oxygen and, once in place, prevents the binding of oxygen. It also turns haemoglobin bright red. The pulse oximeter is unable to distinguish between haemoglobin molecules saturated in oxygen and those carrying carbon monoxide Casey, Pulse oximetry is a quick, noninvasive, and completely painless test.

It comes with no risks, aside from potential skin irritation from the adhesive used in some types of probes. Read this article in Spanish. If you have chronic health conditions, your blood oxygen level may fall outside of the normal range.

This includes people with asthma, heart disease…. Looking for pulse oximeter recommendations? We take a closer look at ChoiceMMed and two of their pulse oximeters that are the easiest to find.

See what finger pulse oximeters our team has chosen to help you keep an eye on your health. Find information on why a blood gas test done, what to expect during the procedure, and how to interpret the test results.

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You can increase iron levels with diet and supplements. Health Conditions Discover Plan Connect. Medically reviewed by Adithya Cattamanchi, M. Takeaway Pulse oximetry is a noninvasive test that measures the oxygen saturation level of your blood. Purpose and uses. How to take a reading.

There has been a shortage of things one might expect: toilet paper, disinfectant wipes, and thermometers. But, there are other—more surprising—items like yoga mats, yeast, and, more recently, pulse oximeters.

So, what, exactly, is a pulse oximeter? Pulse oximeters started to fly off store and online shelves when people learned that low oxygen saturation levels can be a sign of COVID The logic is that shortness of breath, a symptom of the disease, may not be easy—or even possible—for a person to reasonably self-assess.

It happens to patients both in the hospital and at home, but it is a particular problem in the latter case because the symptom may indicate severe COVIDrelated pneumonia, requiring a ventilator. There is debate among doctors about whether or not people need a pulse oximeter in their medical supply kits at home.