PULSE OXIMETRY

PULSE OXIMETRY
What is saturation?
I'm going to talk about ventilation and respiration. Ventilation is done by breathing, which consists of taking O2 from outside to inside, and CO2 from inside to outside, in a very simple way. Ventilation is the main driver of hemodynamics, i.e. blood circulation. Even before the heart, how is the venous return? When I breathe in, the diaphragm pulls on the venous and splanchnic circulation, and brings all the venous blood back to the right heart. It is the first engine of hemodynamics.
CO2 from inside to outside, it’s also to regulate the pH of the body through the carbonic acid buffer. Expired CO2 comes from the CO2 produced by our cellular metabolism in the form of carbonic acid. We continuously produce CO2 through internal combustion that keeps us alive. From carbon chains and oxygen that comes from the atmosphere for cellular metabolism, we manufacture CO2 in the mitochondria to produce energy, ATP.
So we have to transport oxygen to every cell and into the mitochondria, our ATP energy plants. O2 comes quite easily, for example if I do laps in a swimming pool, in apnea, 3 minutes underwater, I will slowly lower my O2 level in the blood, but I will not desaturate. I will still have enough. But in the meantime I'm going to produce a lot of CO2, all the time. The amount of O2 in the blood is called oxemia, and the CO2 in the blood is called capnia.
When I have too much CO2 in my blood, I get hypercapnia. When I don't have enough O2 in my blood, I am hypoxemic.
If I maintain my breathing, or if I re-inhale what I breathe because, for example, I have a mask, I'm going to re-inhale CO2, after a while I get hot, I don't feel very well, I have a feeling of oppression, we are in hypercapnia. Hypercapnia manifests by :
-    arterial hypertension because CO2 is a powerful vasoconstrictor, it presses on the arterioles.
-    It is a powerful vasodilator of the brain, it opens the vessels of the brain. The brain will grow in an inextensible cranium, so the brain will press on the skull and can cause headaches, attention disorders, agitation with an impression of oppression.
When you hold your breath too long, it is not hypoxemia that alerts you, it is hypercapnia. And you have a strong urge to breathe. This can lead to discomfort or even coma.
-    It also induces tachycardia (increased heart rate), sweating, a feeling of heat.
Hypoxemia is much more serious, because if you desaturate, you don't have enough O2 in your blood, the first cells that will feel it are those of the heart, which will stop and you can go into hypoxemic cardiac arrest. But before that you will first have tachycardia, the heart tries to compensate, then bradycardia. And when we desaturate, we have less and less O2 we become blue, cyanosis at the end of the lips, at the end of the nails, it is already a late stage, and after a while the heart slows down and finally stops.
For oxygenation we can see the concentration of O2 in the blood, by a measurement in the arterial blood to measure pO2, this is a blood gas examination. But it is very difficult.
Alternatively, you can look at the amount of O2 in the haemoglobins. The amount of O2 in the red blood cells is the arterial O2 saturation. I can get it from blood gases but I can approach it by "pulsatile oxygen saturation" by pulse oximetry.
  
By colorimetry, by infra-red, we are going to look the quantity of O2 on the red globules. This is what’s important. The heart stops when I desaturate, i.e. when the red blood cells run out of O2, even if there is some left in the blood. I am going to look, with a small clip on the tip of my finger, at a number in 0 and 100, a percentage of oxygen. And below 95% is not normal, and in a child, being below 95% is really not normal.
The problem with masks is much more a problem of capnia, i.e. of the quantity of CO2 which is at the origin of all the symptoms mentioned above. They are the side effects of mask-wearing imposed on children.
The saturation measured by the small clip will give you the % of O2 and the heart rate. If the heart rate is accelerated, this is not normal either. You take the measurement in the morning, for example, before going to school: oxygen saturation and pulse rate of the child.
Then after a day of abuse behind masks, you will see a change in heart rate and a change in oxygenation. If there is a variation in oxygenation, it is very serious: the cells suffer from a chronic lack of O2 with many side effects.
Look at the child's blood pressure, look for signs such as headache, attention deficit disorder, restlessness, malaise, sweat, warmth, discomfort. Note all those signs.
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