AACN Essentials Of Critical Care Nursing Practice Test

Which statement about oxygen saturation (SpO2) is correct?

SpO2 reflects the percentage of dissolved oxygen in plasma SpO2 equals PaO2 SpO2 represents the percentage of hemoglobin bound with oxygen SpO2 is unaffected by hemoglobin status

Correct Answer:

SpO2 represents the percentage of hemoglobin bound with oxygen

Explanation:

SpO2 reflects the percentage of hemoglobin binding sites that are occupied by oxygen, measured noninvasively with pulse oximetry. It does not measure the amount of dissolved oxygen in plasma (that’s PaO2), and it is not the same as PaO2, even though they relate through the oxygen–hemoglobin dissociation curve. SpO2 can be influenced by hemoglobin status—low hemoglobin, or abnormal forms like carboxyhemoglobin or methemoglobin can affect readings—so it isn’t independent of Hb status. Therefore, the statement that SpO2 represents the percentage of hemoglobin bound with oxygen is the correct interpretation.

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