Final answer:
The SpO₂ reading of 90% corresponds to a PO₂ value of approximately B. 60 torr. This reflects hypoxemia, which is a lower than normal level of oxygen in the blood, important in clinical assessment and management of patients receiving oxygen therapy.
Step-by-step explanation:
The student has asked about the correlation between SpO₂ (oxygen saturation) levels and the partial pressure of oxygen (PO₂) in the blood. A SpO₂ reading of 90% obtained from a pulse oximeter typically correlates with a PO₂ value that can be determined using an oxygen-hemoglobin dissociation curve. In this case, a SpO₂ of 90% corresponds roughly to a PO₂ of 60 mm Hg. Therefore, the correct answer to the question is B. 60 torr.
It is important to understand that oxygen saturation as measured by a pulse oximeter and partial pressure of oxygen in the blood are related but not the same. The pulse oximeter uses wavelengths of light to measure the saturation of hemoglobin with oxygen, while PO₂ is measured after an arterial blood sample is taken. Since normal pulse oximeter readings range from 95-100 percent, a reading of 90% indicates hypoxemia, or low blood oxygen, which needs to be addressed in a clinical setting, especially for patients on oxygen therapy.