Noninvasive monitoring of arterial oxygen saturation by pulse oximetry (SpO₂) was first adopted by anesthesiologists in the early 1980s in an effort to optimize patient safety. The goal of this technology was to identify as early as possible unrecognized episodes of hypoxemia (insufficient blood oxygenation) that often resulted in irreversible tissue damage and costly malpractice insurance claims. During the past decade, pulse oximetry has become a rapidly growing practice in many fields of clinical medicine, including subacute and long-term care. Whether used as a safety guard or as a diagnostic tool, this new modality is widely acknowledged to be one of the most important technological advances in patient monitoring. The most important advantage of pulse oximetry is the capability to provide continuous, safe, and cost-effective monitoring of blood oxygenation noninvasively at the patient bedside. It is particularly useful when a patient is unstable and subject to rapid or unpredictable oxygen desaturation. Pulse oximeters are easy to use, require no user calibration, and provide virtually maintenance-free operation.