SpO2 vs. SaO2 ?

  1. 0 My instructor's lecture notes state that SpO2 refers to pulse oximetry, and that SaO2 refers to "peripheral capillary saturation".

    It also says that PaO2 is an invasive procedure used to determine the arterial percentage of blood.

    However...

    my "Fundamentals of Nursing Made Incredibly Easy!" book says that SaO2 denotes "invasively measured arterial oxygen saturation values, such as from arterial blood gas analysis". Now that almost sounds just like the definition of PaO2, above.

    So I guess I'm wondering - is "peripheral capillary saturation" the same thing as pulse oximetry? or no? Does this sound like a typo in my instuctor's outline, or am I just confused? (Yes I'm sure it's the latter, but just humor me..)

    Thanks......
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  3. Visit  Jedi of Zen} profile page

    About Jedi of Zen

    Joined Jul '07; Posts: 277; Likes: 40.

    11 Comments so far...

  4. Visit  Daytonite} profile page
    3
    Very simply, SpO2 is an indirect measurement of the oxygen content of blood (oximetry) where Sao2 is a direct measurement of the oxygen content of the blood (arterial blood gas sampling). I would ask your instructor to clarify what they meant by "peripheral capillary saturation" at the next class meeting since they were the one to use that terminology. However, just hearing it sounds suspiciously like it is referring to pulse oximetry because pulse oximetry is measured at the fingertips where there are peripheral capillaries.
  5. Visit  caliotter3} profile page
    0
    Thanks for these posts. Learned something today.
  6. Visit  Virgo_RN} profile page
    1
    SaO2 can be measured either by ABG analysis or by pulse oximetry. SaO2 refers to the amount of oxygen bound to hemoglobin in arterial blood. SpO2 simply means that the SaO2 was measured using pulse oximetry.
    Sun*shine likes this.
  7. Visit  Jedi of Zen} profile page
    0
    Quote from Daytonite
    Very simply, SpO2 is an indirect measurement of the oxygen content of blood (oximetry) where Sao2 is a direct measurement of the oxygen content of the blood (arterial blood gas sampling). I would ask your instructor to clarify what they meant by "peripheral capillary saturation" at the next class meeting since they were the one to use that terminology. However, just hearing it sounds suspiciously like it is referring to pulse oximetry because pulse oximetry is measured at the fingertips where there are peripheral capillaries.

    Thank you, that does make sense.

    What about PaO2 - where does that fit into all of this? She described it as an "invasive procedure"...I guess I'm wondering how that differs from SaO2.

    I sent my teacher an email several weeks ago and she still has not responded. She has only given about 3 lectures over the semester (this was one of them) and she is usually hard to find at campus.
  8. Visit  Jolie} profile page
    0
    Quote from Jedi of Zen
    Thank you, that does make sense.

    What about PaO2 - where does that fit into all of this? She described it as an "invasive procedure"...I guess I'm wondering how that differs from SaO2.

    I sent my teacher an email several weeks ago and she still has not responded. She has only given about 3 lectures over the semester (this was one of them) and she is usually hard to find at campus.
    Pa02 refers to the partial pressure of 02 in arterial blood. It is measured via artial blood sample. A normal range is approximately 75-100 mm Hg.

    Sa02 refers to oxygen saturation of arterial blood. It is likewise measured by arterial blood sample. A normal value is approximately 95-100%. A pulse-oximeter can be used to continuously monitor a patient's oxygen saturation, and provides a good estimate of Sa02.

    The partial pressure of oxygen in the blood is not the same measurement as the oxygen saturation of blood, but both are indicators of the adequacy of oxygen levels in the patient's blood.

    You can Google "arterial blood gas" to find sites that explain this information more fully.
  9. Visit  Savin'Em} profile page
    0
    Be careful with this. SpO2 and SaO2 are two very different values. Sure, in some patients you can use SpO2 as a guide, but it doesn't always reflect what's actually going on in the blood, such as in cases of patients with septic shock. A good guide to help understand this is the oxyhemoglobin saturation curve.
  10. Visit  scilla} profile page
    0
    I've got the Fundamentals of Nursing textbook, and it says, "The use of a pulse oximeter can provide inormation about the saturation of the client's arterial blood with oxygen (called oxygen saturation or SaO2)." (Harkreader, 2007, p. 129). My Physical Examination and Health Assessment textbook says, "The pulse oximeter is a noninvasive method to assess arterial oxygen saturation (SpO2)." (Jarvis, 2008, p. 169). So, it looks like SaO2 and SpO2 are both measured by the pulse oximeter. So, they must be the same thing.

    It appears that when they draw arterial blood gasses they get PaO2 and PaCO2, which are partial pressures, not percentages (see Harkreader p. 903). I realize this comes a little late for this conversation, but maybe it will help folks like me who are just starting out.
  11. Visit  DrAli} profile page
    0
    At the end of the discussion it gets confusing again!!! lolzzzzzzzz
  12. Visit  ghillbert} profile page
    0
    Oxygen partial pressure (paO2) and saturation (saO2) are 2 different things - read about the difference.

    Saturation can be measure directly/invasively (saO2) or indirectly/peripherally (spO2).
  13. Visit  ALERTMEDIC} profile page
    0
    You may already know this but SaO2 and SpO2 do not measure the same thing. SaO2 is an invasive measure of the % of Oxyhemoglobin(oxygen saturated hemoglobin) in the blood using lab tests on arterial blood. SpO2 noninvasive measure the % of saturated hemoglobin in the capillary bed and does not identify what is saturating the hemaglobin. ie: carboxyhemoglobin, methemoglobin, ect. Typically(in a healthy pt) SaO2 and SpO2 measure the same thing, but a difference can be found in patients with conditions such as CO poisoning and rhabdomyolysis.
  14. Visit  GrnTea} profile page
    1
    it's important to know that saturation is a measure of the percent of rbcs which are carrying oxygen (saturated). so if your s(aturation)p(peripheral)o2 is 98%, then 98% of the rbcs in your peripheral blood (capillaries) carry oxygen on them.

    it's important to know that p(pressure) a(arterial) o2 is the measure of oxygen dissolved in the blood (on the blood cells and to some extent in the serum), most often measured in an arterial blood sample. this has to do with the amount of oxygen that gets out of the air that's breathed into the alveoli and into the blood on the other side of the alveolar capillary bed; it can be increased by increasing the amount of oxygen breathed in (supplemental oxygen) and decreased by decreased alveolar function (like in a pulmonary disease, pneumonia, drowning, etc). it says nothing about the percentage of rbcs carrying oxygen.

    (there's a way to tell how bad your lungs are by looking at the difference between the pao2 that a given supplemental oxygen level should give you if your lungs were normal, and the actual pao2 your crappy diseased lungs actually allow your blood to carry. quick and dirty, your pao2 should be roughly 4-5x the % of oxygen you're breathing; normal pao2 is 80-100 if room air is around 20% oxygen. if you breathe 100% oxygen, your pao2 should measure around 400-500. if it doesn't, your lungs are doing a lousy job of gas exchange. same with any other supplemental level. this is usually called "fio2," "fraction of inspired oxygen;" breathing 60% o2 is an fio2 of .6 and 100% is 1.0, but i digress.)

    the reason that a lot of people get these confused is because normal saturation is 95-100% on room air, and normal pao2 is 80-100 torr or mmhg (note, this is not a percent, it's a pressure measurement) on room air. as your saturation goes down, your pao2 goes down too. please look at this graph:

    http://tinyurl.com/3fzep68

    dang, i wanted that to appear here but you'll have to open it in another window and follow along.this is called the oxyhemoglobin dissociation curve-- it shows the relationship between % saturated hemoglobin and blood oxygen.

    it has the % saturation on the up-down axis and the pao2 (po2 in this graph, same thing for purposes of this discussion) on the side-side axis. as you can see, if your sat is around 95-100%, your pao2 is like 80-100 mmhg (or torr), normal. but if your sat is 90%, your pao2 is down around 60-ish, which is pretty bad, and if it's 80%, your pao2 is in the 40s, which is not really compatible with life for very long at all.

    you can see how if somebody said, "oh, his spo2 is 89, that's fine," she is really wrong, he is not fine.
    i hope this helps you see the relationship between the two and why that is so.

    last.... think about hematocrit. someone with a 98% saturation has 98% of his rbcs carrying oxygen. that's great. but someone in bed a with a hematocrit of 12 is carrying one-third the amount of oxygen to his cells than the guy in the next bed b with a hematocrit of 36, because he only has one-third as much hemoglobin to carry oxygen on. both sats of 95%, but bed a has cells that are getting short on o and bed b is fine. so look at both to see how well your patient is oxygenating his body.

    hope this helps.
    NRKB likes this.


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