The pulse oximeter is one of the most important, yet least understood, patient monitoring advances of the last 25 years. The technology provides a means to easily, quickly, continuously, accurately and non-invasively estimate a patient"s arterial blood saturation level and helps the clinician determine if the patient"s blood is adequately oxygenated. Some clinicians have even said that if, for some reason, they could only have one monitor, SPO2 would be the most important one.