Pulse oximeters estimate the arterial oxygen saturation. Oxygen saturation is the used fraction of the oxygen carrying capacity of the hemoglobin molecules in arterial blood. The oxygen content of the blood should be known to help diagnose certain conditions and help keep oxygen levels appropriate when methods are used to improve blood oxygenation. These methods include oxygen therapy, cpap, and infant ventilation. Too little oxygenation can lead to hypoxia and tissue damage. Too much oxygen can lead to oxygen toxicity--notably affecting the eyes, lungs, and central nervous system.
Mechanism of Action
Pulse oximetry estimates arterial oxygen saturation using the transmission of two wavelengths of light, one red and one infrared. Oxygenated hemoglobin absorbs more infrared than red, whereas reduced hemoglobin does the opposite. The ratio of transmitted wavelengths can be used to approximate oxygen saturation. The most accurate devices perform well under low perfusion, can reject motion artifacts, and can operate on a range of skin colors. In neonates, the most common sensor placement is over the hand or foot. In adults, the sensor is usually placed on a finger.
Pulse oximetry is commonly used in the continuous monitoring of neonates receiving breath support and mothers in a variety of intensive care conditions. To a lesser extent, it can also be used for the differential diagnosis of diseases that have cardio-pulmonary effects.
Current Use in High-Resource Settings
Pulse oximetry has become ubiquitous in high-resource settings. It is used continuously in surgery, monitors many patients, and is carried by some practitioners. In high-resource settings, pulse oximetry is often built into devices which have other capabilities including recording, sounding alarms, or other diagnostic methodologies.
Application in Low-Resource Settings
Pulse oximetry appears in some hospitals and can be immediately useful through the clarity of its reading. However, issues with disposable probes and the integration of oxygenation into diagnostics causes problems in some facilities where practitioners were not trained to add its impact to other tools. Pulse oximetry does have clear benefits for neonates on oxygen and groups including the WHO are advocating for its adoption as standard of care in these situations.
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