Pulse oximetry is a non-invasive method that allows healthcare providers to examine the oxygenation of a patient's blood. It also measures the pulse and the saturation of hemoglobin in the blood. Pulse oximetry was developed half a century ago. However, widespread clinical use of pulse oximeters only became practical with the advent of digital technology. Pulse oximeters began to be commercially marketed in 1981, however their use was principally restricted to critical care areas. Recently, pulse oximetry has been offering reasonably inexpensive, simple, and dependable means to monitor respiratory function and proper oxygen and hemoglobin saturation of the blood in a wide variety of clinical areas, hospitals, and in the community as well. Today, pulse oximetry is very important for assessing emergency patients, determining the effectiveness of supplemental oxygen or the need for it, for use in intensive care settings, and monitoring patients during anesthesia. Pulse Oximeters are the devices that monitor all of these factors. By using a sensor attached to an extremity, the pulse oximeter yields a computerized readout and will sound an alarm if the blood saturation becomes less than optimal. The sensor is placed on a relatively thin part of the anatomy, usually a fingertip or earlobe or in the case of an infant, the foot. A red and infrared light passes from one side of the sensor 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 estimation of oxygenation is made. This is a measure solely of oxygenation, not of ventilation, and is not a substitute for blood gases checked in a laboratory as it provides no indication of carbon dioxide levels, blood pH, or sodium bicarbonate levels. Hypoperfusion of the extremity being used for monitoring, often caused by the extremity being cold or from vein constriction secondary to the use of a vasopressor agent, may account for falsely low readings. Conversely, falsely high readings may take place when the hemoglobin is bound to something besides oxygen (i.e. cases of carbon monoxide poisoning).