Pulse oximetry is a noninvasive method to measure the oxygen saturation of hemoglobin in arterial blood and assess the oxygen delivery to tissues. A pulse oximeter indirectly monitors blood oxygen levels through the skin using light absorption properties of oxygenated and deoxygenated hemoglobin to calculate oxygen saturation. It is useful for continuously monitoring patients at risk for hypoxemia in settings like the ICU, operating room, and emergency department. While generally accurate, readings can be affected by factors like poor perfusion, dyshemoglobins, or excessive motion.