Absorption spectra of oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) for red and infrared wavelengths The inner side of a<unk> imeter A blood-oxygen monitor displays the percentage of blood that is loaded with oxygen. More specifically, it measures what percentage of hemoglobin, the protein in blood that carries oxygen, is loaded. Acceptable normal<unk>  ranges for patients without pulmonary pathology are from 95 to 99 percent. For a person breathing room air at or near sea level, an estimate of arterial<unk> 2 can be made from the blood-oxygen monitor "saturation of peripheral oxygen" <unk>  reading. Mode of operation A typical<unk> imeter uses an electronic processor and a pair of small light-emitting diodes (LEDs) facing a photodiode through a translucent part of the patient's body, usually a fingertip or an earlobe. One LED is red, with wavelength of 660 nm, and the other is infrared with a wavelength of 940 nm. Absorption of light at these wavelengths differs significantly between blood loaded with oxygen and blood lacking oxygen. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin allows more infrared light to pass through and absorbs more red light. The LEDs sequence through their cycle of one on, then the other, then both off about thirty times per second which allows the photodiode to respond to the red and infrared light separately and also adjust for the ambient light baseline. The amount of light that is transmitted (in other words, that is not absorbed) is measured, and separate normalized signals are produced for each wavelength. These signals fluctuate in time because the amount of arterial blood that is present increases (literally<unk> s) with each heartbeat. By subtracting the minimum transmitted light from the transmitted light in each wavelength, the effects of other tissues are corrected for, generating a continuous signal for<unk> tile arterial blood. The ratio of the red light measurement to the infrared light measurement is then calculated by the processor (which represents the ratio of oxygenated hemoglobin to deoxygenated hemoglobin), and this ratio is then converted to<unk>  by the processor via a lookup table based on the Beer–Lambert law. The signal separation also serves other purposes: a plethysmograph waveform ("pleth wave") representing the<unk> tile signal is usually displayed for a visual indication of the<unk> s as well as signal quality, and a numeric ratio between the<unk> tile and baseline absorbance ("perfusion index") can be used to evaluate perfusion. where HbO2 is oxygenated hemoglobin (oxyhemoglobin) and Hb is deoxygenated hemoglobin. Derived measurements Due to changes in blood volumes in the skin, a plethysmographic variation can be seen in the light signal received (transmittance) by the sensor on an oximeter. The variation can be described as a periodic function, which in turn can be split into a DC component (the peak value) and an AC component (peak minus trough). The ratio of the AC component to the DC component, expressed as a percentage, is known as the (peripheral) perfusion index (Pi) for a<unk> , and typically has a range of 0.02% to 20%. An earlier measurement called the<unk>  plethysmographic <unk> P) only measures the "AC" component, and is derived manually from monitor pixels. Pleth variability index (PVI) is a measure of the variability of the perfusion index, which occurs during breathing cycles. Mathematically it is calculated as , where the maximum and minimum Pi values are from one or many breathing cycles. It has been shown to be a useful, noninvasive indicator of continuous fluid responsiveness for patients undergoing fluid management.<unk>  plethysmographic waveform amplitude (ΔPOP) is an analogous earlier technique for use on the manually-derived<unk> P, calculated as .
Pulse oximetry
Plethysmograph
Oxygenation index
Hyperoxia test
Oxygen saturation 
Oxygen saturation
Fraction of inspired oxygen
Respiratory pressure meter