Pulse oximetry SpO2 refers to the percentage of blood oxygen content and blood oxygen capacity. SpO2 has been recognized as a non-invasive, fast-responding, safe, and reliable continuous monitoring indicator.
It is currently widely used in anesthesia, surgery, and PACU and ICU. According to the spectral characteristics of oxyhemoglobin (HbO2) and reduced hemoglobin (Hb) in the red and infrared regions, it can be seen in the red region (600~
700nm) The absorption of HbO2 and Hb is very different. The degree of light absorption and the degree of light scattering of blood are greatly dependent on oxygen saturation. In the infrared region (800~1000nm), the absorption difference is large, and the degree of light absorption of blood is large. The degree of light scattering is mainly related to the hemoglobin content. Therefore, the absorption spectra of HbO2 and Hb are different. Therefore, the blood in the blood catheter of the oximeter can be based on HbO2 and Hb, whether it is arterial blood or venous blood saturation meter. The content accurately reflects the hemorrhage oxygen saturation.
The ratio of blood reflection near the wavelength of 660nm and around 900nm (ρ660/900) most sensitively reflects the change of hemorrhage oxygen saturation. Clinical general oximeter (such as Taijia saturation meter, pulse oximeter) This ratio is also used as a variable. In the light-conducting pathway, in addition to arterial hemoglobin absorbs light, other tissues (such as skin, soft tissue, venous blood, and capillary blood) can also absorb light. However, when the incident light passes through the finger or the earlobe, the light can be absorbed by the pulsating blood and other tissues at the same time, but the light intensity absorbed by the two is different, and the light intensity (AC) absorbed by the pulsating arterial blood changes with the arterial pressure wave. And change.
The light intensity (DC) absorbed by other tissues does not change with the beat and time, and thus, the light absorption ratio R at two wavelengths can be calculated. R = (AC660 / DC660) / (AC940 / DC940). R is negatively correlated with SpO2. According to the R value, the corresponding SpO2 value can be obtained from the standard curve.