what is being measured when using a pulse oximeter
Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation (SO). Though its reading of SpO (peripheral oxygen saturation) is not always identical to the more desirable reading of SaO (arterial oxygen saturation) from arterial blood gas analysis, the two are correlated well enough that the safe, convenient, noninvasive, inexpensive pulse oximetry method is valuable for measuring oxygen saturation in clinical use.