This. If the waveform is good, I will consider the SpO2 reading as part of the assessment. If not, it means nothing to me. However, if there is any doubt or if the initial SpO2 is low, I will use ETCO2 to see what's really going on and to help me choose a treatment plan. Also, you can try moving your sensor around to different fingers (or toes) and see what type of results you get. If you have the hard sensors, try using one of the disposable ones to obtain a better reading.