Oxygen saturation – better measured than calculated
Haemoglobin carries oxygen in the blood. mafiathegame.info is charity-funded and written by independent doctors. The haemoglobin–oxygen dissociation curve describing the relationship between oxygen partial pressure and saturation can be modelled mathematically and. The oxygen dissociation curve (ODC) describes this relationship graphically (see The percentage of total hemoglobin that is saturated with oxygen (i.e. oxygen .. This same advice is contained in guidelines from the Clinical and Laboratory .
A fuller and more accurate assessment of blood oxygenation is offered by arterial blood gas analysis.
Relating oxygen partial pressure, saturation and content: the haemoglobin–oxygen dissociation curve
Oxygen saturation is just one of several oxygen-related parameters generated during blood gas analysis. Oxygen saturation is generated during blood gas analysis by one of two methods: The calculation used to generate sO2 from pO2 a is based on the relationship between the two described by the oxygen dissociation curve.
The oxygen dissociation curve is affected by a number of factors other than pO2 and sO2 that may be in a state of considerable flux during critical illness, rendering calculated sO2 potentially inaccurate. Measured sO2 by CO-oximetry is unaffected by these fluxes; it is the method of choice for determining oxygen saturation and the most commonly used nowadays most modern blood gas analyzers have an incorporated CO-oximeter Clinicians should be aware of the method used to generate sO2 during blood gas analysis at their institution.
If the method is calculation from measured pO2, then sO2 values from critically ill patients should be interpreted with caution. Discrepancy between pO2 a and calculated sO2 for example, one indicating hypoxemia and the other indicating normoxemia suggests an inaccurate calculated sO2 a value. References Gutierrez J, Theidorou A. Oxygen delivery and oxygen consumption in Pediatric Critical Care.
Pediatric Critical Care Study Guide. Springerchapter 2. Crit Care Med ; 31, Ranney H, Aharma V. Structure and function of hemoglobin, In: Performance of an automated six wavelength photometer Radiometer OSM3 for routine measurement of hemoglobin derivatives.
Clin Chem ; Oxygen saturation calculation procedures: Intensive Care Medicine ; Myoglobin, in muscle cells, accepts, stores, transports and releases oxygen.
Oxygen–hemoglobin dissociation curve
About 6 percent of body iron is a component of certain proteins, essential for respiration and energy metabolism, and as a component of enzymes involved in the synthesis of collagen and some neurotransmitters. Iron also is needed for proper immune function.
About 25 percent of the iron in the body is stored as ferritin, found in cells and circulates in the blood. The average adult male has about 1, mg of stored iron enough for about three yearswhereas women on average have only about mg enough for about six months. When iron intake is chronically low, stores can become depleted, decreasing hemoglobin levels.
When iron stores are exhausted, the condition is called iron depletion. Further decreases may be called iron-deficient erythropoiesis and still further decreases produce iron deficiency anemia. Blood loss is the most common cause of iron deficiency. It's got four parts to it. And each part can bind an oxygen.
So hemoglobin, I can shorten this to Hb. Now, oxygen is going to bump into, quite literally bump into one of these hemoglobins. And it's going to bind, let's say, right here. And initially, it's kind of tricky because oxygen doesn't feel very comfortable sitting on the hemoglobin or binding to hemoglobin. But once a single oxygen is bound, a second one will come and bind as well. And then a third will find it much easier. Because what's happening is that as each oxygen binds, it actually changes the conformation or shape of hemoglobin.
And so each subsequent oxygen has an easier time binding. We call that cooperativity. Has the word, almost like cooperation in it. And an easy way to think of cooperativity, the way I think of it, is that if you're at a dinner party, you are much more likely to sit where two or three of your friends are already sitting, if you think of this as a table with four chairs, rather than just sitting at a table by yourself being the first one to sit there. So we kind of like sitting with our friends and oxygen is kind of a friendly molecule.
And so it also likes to sit where or bind where other oxygens have already bound. What are the two, then, major ways, based on this diagram, how I've drawn it. What are the two major ways that oxygen is going to be transported in the blood? One is hemoglobin binding oxygen. And we call that HbO2. Just Hb for hemoglobin, O2 for oxygen. And this molecule, or this enzyme, then, is not really called hemoglobin anymore. Technically, it's called oxyhemoglobin.
Hemoglobin and Functions of Iron | Patient Education | UCSF Medical Center
That's the name for it. And another way that you can actually transport oxygen around is, that some of this oxygen-- I actually underlined it there-- is dissolved, O2 is dissolved in plasma. So some of the oxygen actually just gets dissolved right into the plasma. And that's how it gets moved around. Now, the majority, the vast majority of it is actually going to be moved through binding to hemoglobin.
So just a little bit is dissolved in the plasma. The majority is bound to hemoglobin. So this red blood cell goes off to do its delivery. Let's say, it's delivering some oxygen out here. And there is a tissue cell.
And, of course, it doesn't know where it's going to go that day. But it's going to go wherever its blood flow takes it. So let's say, it takes a pass over to this thigh cell in your, let's say, upper thigh. So this thigh cell has been making CO2.
And remember, sometimes we think of CO2 as being made only when the muscle has been working. But you could be napping. You could be doing whatever. And this CO2 is still being made because cellular respiration is always happening.
So this red blood cell has moved into the capillary right by this thigh cell. So you've got a situation like this where now some of the CO2 is going to diffuse into the red blood cell like that. And what happens once it gets down there?
So let me draw out, now, a large version of the red blood cell. Just so you get a closer view of what's going on. And we're in the thigh and the two big conditions in the thigh that we have to keep in mind. One is that you have a high amount of CO2 or partial pressure of CO2. And this is dissolved in the blood. And the other is that you have a low amount of oxygen, not too much oxygen in those tissues.
So let's focus on that second point. If there's not too much oxygen in the tissues, and we know that the hemoglobin is kind of constantly bumping into oxygen molecules and binding them.
And they fall off and new ones bind. So it's kind of a dynamic process. Now, when there's not too much oxygen around, these oxygen molecules are going to fall off as they always do in a dynamic situation. Except new ones are not going to bind. Because there's so little oxygen around in the area, that less and less oxygen is free and is available to bump into hemoglobin and bind to it.
So you're going to literally start getting some oxygen that falls off the hemoglobin simply because the partial pressure of oxygen is low. So one reason for oxygen to come into the cells is going to be a low pO2. So these are reasons-- and I'm going to give you another one, that's why I'm writing reasons-- for O2 delivery.
So one of them is going to be simply not having too much oxygen in that area.
A second reason has to do with CO2 itself. So let's actually follow what happens once CO2 starts getting into the red blood cell.
Now, this first CO2 molecule, it's going to meet up with a little water. Remember, there's a lot of water in the red blood cell.
Hemoglobin moves O2 and CO2 (video) | Khan Academy
In fact, there's water all over the blood. In fact, it's made of mostly water. And so it's not too hard to imagine that a water molecule might bump into this CO2. And there's an enzyme called carbonic anhydrase. Now, if it's an acid, try to keep in mind what acids do. Acids are going to kick off a proton.