Always keep SpO2 < 100% (with rare exception).
An SpO2 between 92% to 99% says something about your patient’s condition.
SpO2 PaO2 FiO2 P/F ratio
100 % 600 100% 600
100% 500 100% 500
100% 400 100% 400
100% 300 100% 300
100% 200 100% 200
100% 100 100% 100
99% 90 100% 90
98% 87 100% 87
97% 85 100% 85
96% 82 100% 82
95% 80 100% 80
90% 60 100% 60
Look at your patient’s SpO2 > this will allow you to approximate both your patient’s PaO2 and P/F ratio.
If your patient’s spo2 = 90%, your patient’s PaO2=60mmHg.
If your patient’s spo2=99%, your patient’s PaO2=90mmHg.
So if your patient’s SpO2 = 97% and the FiO2=40%, you can estimate the P/F ratio as ~80/0.4=200.
If your patient’s SpO2=100%, your PaO2 can be anywhere from 90 to 600 > this is no help because you cannot approximate, let alone pinpoint, the pao2.
So, your patient with an SpO2=100% is not very telling of the patient condition.
If your patient’s spo2=100% and the pao2=100, on an fio2=40%, the p/f ratio=100/0.4=250 (=ALI = acute lung injury).
if your patient’s spo2=100% and the pao2=240, on an fio2=40%, the p/f ratio=240/0.4=600 (= normal).