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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  2. 11 Comments...

  3. 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.
  4. 0
    Thanks for these posts. Learned something today.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
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    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.
  10. 0
    At the end of the discussion it gets confusing again!!! lolzzzzzzzz
  11. 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).


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