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Thread: pulse oximetry

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    pulse oximetry

    anyone know of actual research done looking at correlations of inspired PO2 and pulse oximetry (via ear or finger probe)

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    Re: pulse oximetry

    In my experience as an intensive care nurse pulse oximetry Would have very limited use healthy lungs on air give a reading of 98 to 100%. 100% being the highest they read.

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    Re: pulse oximetry

    Quote Originally Posted by OceanOpportunity  View Original Post
    anyone know of actual research done looking at correlations of inspired PO2 and pulse oximetry (via ear or finger probe)
    It's only looking at the colour of the hemoglobin in the blood and a few days in a cardiac ward taught me that it read 98% for me and everybody.

    Breathing more than 0.21bar ppO2 it's probably jammed against the end stop with enough dissolved O2 that the circulation probably never needs the hemoglobin transport mechanism. It might tell you you'e about to go hypoxic but hyperoxic is the real problem.

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    Re: pulse oximetry

    Quote Originally Posted by OceanOpportunity  View Original Post
    anyone know of actual research done looking at correlations of inspired PO2 and pulse oximetry (via ear or finger probe)
    If what you're asking about is the corelation between actual arterial PO2 and oximetry then the answer is that there is surprisingly little data.

    What do you actually want to know?

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    Re: pulse oximetry

    Quote Originally Posted by nigelh  View Original Post
    It's only looking at the colour of the hemoglobin in the blood and a few days in a cardiac ward taught me that it read 98% for me and everybody.

    Breathing more than 0.21bar ppO2 it's probably jammed against the end stop with enough dissolved O2 that the circulation probably never needs the hemoglobin transport mechanism. It might tell you you'e about to go hypoxic but hyperoxic is the real problem.
    Thinking out loud, so in hyperbaric situation if you get an O2 pulse you are close to hypoxia, interesting, , its a shame not to have a similar method for CO2, perhaps easiest to monitor that than CO2 in the loop...
    An other problem would be where to place the sensor during a dive

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    Re: pulse oximetry

    Quote Originally Posted by nigelh  View Original Post
    Breathing more than 0.21bar ppO2 it's probably jammed against the end stop with enough dissolved O2 that the circulation probably never needs the hemoglobin transport mechanism.
    Uh, no.

    Dissolved oxygen (in the plasma) is not sufficient on its own until you get up somewhere around 3.0 PO2, and by that point you've probably toxed!

    Hemoglobin transport is one of those amazing physiological things without which we'd all be dead......

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    Re: pulse oximetry

    A pulse oximeter measures the ratio of oxygenated to total haemoglobin. So when it says 98% it means that 98% of the total (arteriolar) haemoglobin has oxygen bound to it.

    Haemoglobin binds oxygen very well and is well saturated even at surprisingly low partial pressures of oxygen.

    In rebreather use, where we use FIO2's much higher than atmosheric air, our haemoglobin is 100% saturated with oxygen all the time.

    A fall in oxygen saturation would be a very late sign of loop hypoxia (only seen when the FIO2 falls below about 0.15 ATA), and therefore of very little use.

    Dave T

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    Re: pulse oximetry

    Quote Originally Posted by dteubner  View Original Post
    A pulse oximeter measures the ratio of oxygenated to total haemoglobin. So when it says 98% it means that 98% of the total (arteriolar) haemoglobin has oxygen bound to it.

    Haemoglobin binds oxygen very well and is well saturated even at surprisingly low partial pressures of oxygen.

    In rebreather use, where we use FIO2's much higher than atmosheric air, our haemoglobin is 100% saturated with oxygen all the time.

    A fall in oxygen saturation would be a very late sign of loop hypoxia (only seen when the FIO2 falls below about 0.15 ATA), and therefore of very little use.

    Dave T
    sorry to the OP to go off-topic

    Dave
    On one of my trips to the chamber, i was sitting at the emergency ward and my %oxygenation was 93%. This caused some concern in relation to a possible lung perforation, so i was then subjected to chest x-ray. However the oximeter was placed on my finger that had a not-quite-recently blackened fingernail (when it met hammer). could that have interfered? Just wondering really.

    rachel

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    Re: pulse oximetry

    Quote Originally Posted by bendomatic  View Original Post
    sorry to the OP to go off-topic

    Dave
    On one of my trips to the chamber, i was sitting at the emergency ward and my %oxygenation was 93%. This caused some concern in relation to a possible lung perforation, so i was then subjected to chest x-ray. However the oximeter was placed on my finger that had a not-quite-recently blackened fingernail (when it met hammer). could that have interfered? Just wondering really.

    rachel
    Hi Rachel,

    Short answer - yes.

    Longer answer - the way the oximeter works is it shines two lights through the finger, one red and one near infrared. The amount of light which goes through the finger is detected by sensors. Oxygenated and deoxygenated haemoglobin absorb the lights differently and the ratio of the signal from the two sensors is used to determine what the oxygen saturation. The machine is clever in that it only uses the bit of the signal whcih fluctuates with time (i.e the pulseatile bit) to eliminate the absorption from skin, bone, venous blood etc.

    Anything that can absorb the light can potentially interfere with the signal and so maybe affect results. This might include nail polish, bruise under the nail etc. The other point is that, because the machine relies on pulsatile flow, anything which reduces blood flow to the fingers (cold, anxiety, low blood pressure) will make the reading less accurate.

    If you were on oxygen and the machine was saying 93%, then it almost certainly was an error, assuming your lungs were OK.

    Dave

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    Re: pulse oximetry

    no problems with the lungs which is why i've wondered. but at least it got the staff treating me a little more seriously. ;)

    also thanks for the long answer.

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