Oxygen saturation in the blood

February 24, 2020

Oxygen is an essential gas for our survival, which must be present in sufficient quantity in our organism for optimal functioning of the organs. Oxygen saturation is a value used to ensure that the red blood cells are sufficiently loaded with this gaseous element.

The human body needs oxygen to ensure its normal functioning. But having a good exchange system in the lungs is not enough for cells to get the oxygen they need. You also need a transportation system to get it there. These are the red blood cells that provide this transport. They are 33% made up of a protein called hemoglobin.

Each hemoglobin molecule carries four iron atoms, which can each bind to one oxygen molecule. When oxygen binds to iron, the red blood cell is "loaded" with oxygen and turns a bright red color. We're talking about oxyhemoglobin. Once the oxygen has been supplied to the tissues, the red blood cell is almost discharged of its oxygen and we then speak of deoxyhemoglobin.

The pulse oximeter is the device that will be used to measure the filling rate of these buses and therefore the adequate oxygenation of the tissues.

Oxygen saturation

In order to check the good oxygenation of the tissues, we measure the quantity of oxygen that the red blood cells transport, it is the oxygen saturation.

Be careful not to confuse:

Oxygen saturation (SAO2)

It is the measurement of hemoglobin saturation by arterial blood sampling. This second technique requires an act performed by a doctor or a nurse. It is currently the only technique that allows a reliable and definitive measurement of blood gases.

Pulsed oxygen saturation (SpO2)

It is the saturation of hemoglobin with oxygen by pulse oximetry.

A tool, the pulse oximeter or saturometer, provides an approximation of the arterial oxygen saturation, without having to draw a blood sample. Through the skin, it more accurately measures pulsed oxygen saturation (SpO2), a more or less perfect reflection of SAO2.

The values ​​of these measures are expressed as a percentage.

This table does NOT apply to people with certain prior illnesses (e.g. asthma, heart failure, respiratory tract diseases) and when staying at altitudes above 1500 meters. If you already have an illness, always consult your doctor for evaluation of your results.Contact your doctor if you have any doubts about your results.

The special case of the mountain

Oxygen saturation also varies with altitude. As you go up in altitude, towards the top of a mountain, theair contains less and lessoxygen. This is because the air pressure decreases. When the pressure is lower, the same volume air contains less than molecules, so less oxygen.

The following table informs you of the effects of different altitudes on the value of pulsed oxygen saturation as well as their consequences for the human organism.

This table does NOT apply to people with certain prior illnesses (e.g. asthma, heart failure, respiratory tract diseases) and when staying at altitudes above 1500 meters. If you already have an illness, always consult your doctor for evaluation of your results.Contact your doctor if you have any doubts about your results.

How to take the measurement with a pulse oximeter

  • Remove the varnish on the nails and false nails because the result can be distorted.

  • Install the sensor preferably on the fingers or toes but not on the thumb or big toe.

  • Position the sensor so that the light is on top of the nail and the photodetector below the finger or toe.

  • Warm the extremities of the limbs, if necessary, to get a better pulse signal.

  • Reduce the lighting, because too strong light distorts the signal

Certain situations may modify the result: low hemoglobin, peripheral hypoperfusion, vasoconstrictor drugs (adrenaline), hypovolemia, hypothermia, agitation.