The Sao2 is the percent of oxygen bound to the heme portion of hemoglobin.
Neither the amount of hemoglobin, nor the binding characteristics of hemoglobin, should affect the amount of dissolved oxygen, and hence should not affect the PaO2). Stated another way, the number of dissolved oxygen molecules is independent of the amount of hemoglobin or what is bound to it. To repeat one more time (because it is so important), PaO2 is not a function of hemoglobin content or of its characteristics, but only of the alveolar PO2 and the lung architecture (alveolar-capillary interface). This explains why, for example, patients with severe anemia or carbon monoxide poisoning or methemoglobinemia can (and often do) have a normal PaO2.
Thus hemoglobin is like an efficient sponge that soaks up oxygen so more can enter the blood. Hemoglobin continues to soak up oxygen molecules until it becomes saturated with the maximum amount it can hold - an amount that is largely determined by the PaO2
Why wouldn't Pao2 and Sa02 vary inversly? It seems to me that if a low Sao2 existed(due to a deficiency of Hb, or inability of oxygen to bind to the Hb), one would find a higer Pa02, as no oxygen molecules are being removed from the plasma?
Would Co2 poisoning result in a low sa02, and a higher Pa02 as the heme bonding sites are occupied, thus preventing oxygen from bonding with hemeglobin?
Several sources seem to use Sp02 and Sa02 interchangebly. Spo2 and Sa02, while similiar, should represent 2 entirely differnet values, correct? If a patient has an Sp02/Sa02 level within an acceptable range, would that indicate that the Pa02 is also satisfactory?
Does the Ca02, simply combine the data gathered by the sa02 and the Pao2, in to a quantifiable amount?
If Cao2 is calculated with the following amount, would it stand to reason that a patient could be found to have an adequate Sa02 or Pao2 and still "not be oxygneating properly"?
CaO2 = Hb (gm/dl) x 1.34 ml O2/gm Hb x SaO2 + PaO2 x (.003 ml O2/mm Hg/dl).
Thank you in advance, and I hope my questions were phrased in a way that made sense to those of you reading(I can't seem to disable the bold font, so that is why this is typed boldly)
Edited by LifeguardsForLife, 27 December 2009 - 08:27 PM.