Pulse oximetry is a noninvasive, accurate, and safe method for the measurement of oxygen saturation during intravenous sedation or general anesthesia. Several factors should be considered with its use, since these variables will either alter the accuracy of the readings or may cause harm to the patient. These factors include changes in the strength of the arterial pulse, body movements, dyshemoglobinemias, plasma lipids and bilirubin, color interferences, venous pulsations, and several physical factors. Awareness of these variations will help the clinician become more knowledgeable in the use of the pulse oximeter.