<unk>  solely measures hemoglobin saturation, not ventilation and is not a complete measure of respiratory sufficiency. It is not a substitute for blood gases checked in a laboratory, because it gives no indication of base deficit, carbon dioxide levels, blood pH, or bicarbonate (HCO3−) concentration. The metabolism of oxygen can be readily measured by monitoring expired CO2, but saturation figures give no information about blood oxygen content. Most of the oxygen in the blood is carried by hemoglobin; in severe anemia, the blood contains less hemoglobin, which despite being saturated cannot carry as much oxygen. Because<unk> imeter devices are calibrated in healthy subjects, the accuracy is<unk> or for critically ill patients and preterm newborns. Erroneously low readings may be caused by hypoperfusion of the extremity being used for monitoring (often due to a limb being cold, or from vasoconstriction secondary to the use of vasopressor agents); incorrect sensor application; highly calloused skin; or movement (such as shivering), especially during hypoperfusion. To ensure accuracy, the sensor should return a steady<unk>  and/or<unk>  waveform.<unk>  technologies differ in their abilities to provide accurate data during conditions of motion and low perfusion. Obesity, hypotension (low blood pressure), and some hemoglobin variants can reduce the accuracy of the results. Some home<unk> imeters have low sampling rates which can significantly underestimate dips in blood oxygen levels. The accuracy of<unk>  deteriorates considerably for readings below 80%.<unk>  also is not a complete measure of circulatory oxygen sufficiency. If there is insufficient bloodflow or insufficient hemoglobin in the blood (anemia), tissues can suffer hypoxia despite high arterial oxygen saturation. Since<unk>  measures only the percentage of bound hemoglobin, a falsely high or falsely low reading will occur when hemoglobin binds to something other than oxygen: * Hemoglobin has a higher affinity to carbon monoxide than it does to oxygen, and a high reading may occur despite the patient's actually being hypoxemic. In cases of carbon monoxide<unk> isoning, this inaccuracy may delay the recognition of hypoxia (low cellular oxygen level). * Cyanide<unk> isoning gives a high reading because it reduces oxygen extraction from arterial blood. In this case, the reading is not false, as arterial blood oxygen is indeed high in early cyanide<unk> isoning. * Methemoglobinemia characteristically causes<unk>  readings in the mid-80s. * COPD especially chronic bronchitis may cause false readings. A noninvasive method that allows continuous measurement of the dyshemoglobins is the<unk>  CO-oximeter, which was built in 2005 by Masimo. By using additional wavelengths, it provides clinicians a way to measure the dyshemoglobins, carboxyhemoglobin, and methemoglobin along with total hemoglobin. Research has suggested that error rates in common<unk> imeter devices may be higher for adults with dark skin color, leading to claims of encoding systemic racism in countries with multi-racial<unk> pulations such as the United States.<unk>  is used for the screening of sleep apnea and other types of sleep-disordered breathing which in the United States are conditions more prevalent among minorities. Equipment In addition to<unk> imeters for professional use, many inexpensive "consumer" models are available. Opinions vary about the reliability of consumer oximeters; a typical comment is "The research data on home monitors has been mixed, but they tend to be accurate within a few percentage<unk> ints". Some smart watches with activity tracking incorporate an oximeter function. An article on such devices, in the context of diagnosing COVID-19 infection, quoted João Paulo Cunha of the University of<unk> rto,<unk> rtugal: "these sensors are not precise, that's the main limitation ... the ones that you wear are only for the consumer level, not for the clinical level".<unk> imeters used for diagnosis of conditions such as COVID-19 should be Class IIB medical grade oximeters. Class IIB oximeters can be used on patients of all skin colors, low pigmentation and in the presence of motion. When a<unk> imeter is shared between two patients, it should be either cleaned with alcohol wipes after each use or a disposable probe or finger cover to be used to prevent cross-infection. According to a report by iData Research the US<unk>  monitoring market for equipment and sensors was over $700 million in 2011. Mobile apps Mobile app<unk> imeters use the flashlight and the camera of the phone, instead of infrared light used in conventional<unk> imeters. However, apps don't generate as accurate readings because the camera can't measure the light reflection at two wavelengths, so the oxygen saturation readings that are obtained through an app on a smartphone are inconsistent for clinical use. At least one study has suggested these are not reliable relative to clinical<unk> imeters.
Pulse oximetry
Plethysmograph
Oxygenation index
Hyperoxia test
Oxygen saturation 
Oxygen saturation
Fraction of inspired oxygen
Respiratory pressure meter