Pulse oximetry is a non-invasive method which allows health care providers to monitor the oxygenation of a patient's blood. A sensor is placed on a relatively thin part of the patient's anatomy, usually a fingertip or earlobe, and red and infrared light is passed from one side to the other. Based upon the ratio of absorption of the red and infrared light caused by the difference in color between oxygen-bound (red) and unbound (blue) hemoglobin in the capillary bed, an approximation of oxygenation can be made. This is especially useful in an intensive care setting, for asssessment of emergency patients, determining the effectiveness of or need for supplemental oxygen, and monitoring during anesthesia.