A patient receiving mechanical ventilation is being continuously monitored for oxygen saturation measured by pulse oximeter (SpO2) for the past 48 hours

When initially applied, the SpO2 and the arterial oxygen saturation (SaO2), as well as the pulse on the pulse oximeter, ECG, and manual pulse, were consistent. During clinical rounds, the respira-tory therapist notices that although the probe is appropriately placed and capillary refill is normal, the SpO2 reading is down to 90% from 95%. The most appropriate immediate action is to do which of the following?
a. Replace the probe.
b. Reposition the patient.
c. Draw an arterial blood gas.
d. Move the probe to a different site.

ANS: C
The oxygen saturation measured by pulse oximeter (SpO2) has dropped from 95% to 90%. Since the SpO2 and arterial oxygen saturation (SaO2) previously correlated, this situation could mean that the patient is becoming hypoxemic. The probe is appropriately placed, so changing sites is not appropriate. The patient has already been checked for and has adequate circulation to the site of the probe, so moving the probe to a site with more perfusion is not appropriate. Therefore, the patient needs to have an arterial blood gas to ascertain the SaO2 and partial pressure of oxygen (PaO2).