Pulse ox + Sickle cell anemia

adamjh3

adamjh3

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Quick question, We discussed PulseOx today. My teacher brought up the extreme example of someone breathing straight carbon monoxide, then getting an O2 saturation reading, (I know, wouldn't happen, but just for the sake of argument) it would come back good, because it's detecting that SOMETHING is being carried by the RBCs.

My book says the Pulse Oximeter is a "photoelectric" device. Breaking that word down, I'm assuming it somehow takes an image of the RBCs, and detects that O2 is being carried by them. So would a Pulse Oximeter be able to get an "accurate" reading on someone with sickle cell anemia, or any other disease that would alter the shape of RBCs?
 
The pulseOx detects the amount of O being carried. It will give you a number of it. I do not believe that it measures the shape of the hemoglobin, from what my instructer said, it is just measuring the amount of the O2 or O in the blood. It is not just something, but that specific thing. -- it would say that you have near 100% pulseOx if you are breating in straight carbon monoxide, because it is only measuring the amount of O in the blood, and CO attaches to hemoglobin faster and stronger then O2, --

-- unless the altered shape affects how much the O attaches to it, or the amount of it that can attach, I don't see how it could affect the pulseOx.
 
katja said:
The pulseOx detects the amount of O being carried. It will give you a number of it. I do not believe that it measures the shape of the hemoglobin, from what my instructer said, it is just measuring the amount of the O2 or O in the blood.
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Your instructor is wrong if that's how he's explaining it. A basic pulse oximeter measures the amount of saturated hemoglobin, not the oxygen in the blood. As such, it doesn't care if the blood is saturated with CO or O2 (however the more expensive models can tell the difference). Similarly, if the patient is anemic, they can have a SpO2 of 100% and still be hypoxic.
 
Pulse ox uses a colorimeter to test the redness of the blood.

The color red is calibrated against what oxygenated blod looks like to the colorimeter.

CO makes blood nice and red, and it's affinity for RBC's is hundreds of times greater than O2, but it does not want to dissociate. Similarly, if your pt's pH is too high (basic), since O2 won't want to dissociate into tissue, it may make the pulse ox (and mucosae and skin color) look good when actually the RBC's are flying past the tissues teasing them with O2 they won't give up...effectively smothering you while you are saturated with oxygen. (To a point).

Since CO has such a high RBC affinity, you do not need 100% CO for this sort of poisoning to occur. Been there seen that.
 
I have actually transported a young child with sickle cell and had a few during my pedi rotations and the pulse ox on the truck and in the hospital were both altered. In each situation the child received supplimental O2 and were watched for resp distress signs and symptoms.
 
Awesome, thanks for the information, everyone. Should I be disturbed that my instructor that night (who is a Paramedic) couldn't answer this quesiton?
 
I would be concerned if he was confusing oxygen carring capacity (of which satuartion percent is a component, but so is the hemiglobin concentration) and percent saturation when interpreting a pulse oximeter reading.
 
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