SpO2 measures blood oxygen saturation levels. Normal is between 95-99%, and the only way to achieve 100% is with supplemental oxygen. Once you know the SpO2 value, you can estimate the arterial PO2 value using the 4-5-6-7-8-9 rule. For example:
SpO2 70% = PO2 of 40
SpO2 80% = PO2 of 50
SpO2 90% = PO2 of 60
SpO2 100% (our patient) = PO2 of 70.
If the SpO2 were to drop a bit from 100%, the PO2 would also drop a bit. The range of possible PO2 values in our patient is: 60-70.
