The basic principle of blood oxygen saturation detection
Oxygen is the foundation of human life. The contraction and relaxation of the heart causes the blood of the human body to pulsate through the lungs. A certain amount of reduced hemoglobin (HbR) combines with the oxygen taken up in the lungs to form oxygen and hemoglobin (HbO2). About 2% of the oxygen is dissolved in the plasma. This blood is transported through the arteries to the capillaries and then releases oxygen in the capillaries to maintain the metabolism of the tissue cells. Blood oxygen saturation (SpO2)
It is the capacity of oxygen-bound oxyhemoglobin (HbO2) in the blood to account for all bindable hemoglobin (Hb).
The percentage of volume, the concentration of blood oxygen in the blood, is an important physiological parameter of the respiratory cycle. Functional oxygen saturation is the ratio of HbO2 concentration to HbO2 Hb concentration, which is different from the percentage of oxyhemoglobin. Therefore, monitoring arterial oxygen saturation (SaO2) can estimate lung oxygenation and hemoglobin oxygen carrying capacity.
Blood oxygen saturation detection classification
The measurement of blood oxygen concentration is generally divided into two types: electrochemical method and optical method.
The traditional electrochemical method of measuring oxygen saturation is to first collect blood from the human body (the most commonly used is to take arterial blood), and then use the blood gas analyzer for electrochemical analysis, and measure the partial pressure of arterial oxygen (PaO2) within a few minutes. And calculate arterial oxygen saturation (SaO2). Because this method requires arterial puncture or intubation, it causes pain to the patient and cannot be continuously monitored, so when it is in a dangerous situation, it is not easy for the patient to receive timely treatment. The advantage of the electrochemical method is that the measurement result is accurate and reliable, the disadvantage is that it is cumbersome and cannot be continuously monitored, and is a damaged oximetry method.
Optical method is a new optical measurement method that overcomes the shortcomings of electrochemical method. It is a continuous non-invasive blood oxygen measurement method, which can be used in emergency ward, operating room, recovery room and sleep research. At present, pulse oximetry (Pulse Oximetry) is used. The principle is to detect changes in blood absorption by light, and to measure the percentage of total hemoglobin (Hb) in oxyhemoglobin (HbO2). Get SpO2. The advantage of this method is that it can continuously measure the human body without damage, and the instrument is simple and convenient to use, so it has been paid more and more attention. The disadvantage is that the measurement accuracy is lower than that of the electrochemical method, and the error caused by the lower blood oxygen value is large. Ear oximeters, multi-wavelength oximeters and the newly introduced pulse oximeter have appeared. The measurement error of the latest pulse oximeter can be controlled within 1% to meet the requirements of clinical use. Although they are not satisfactory in some respects, their clinical benefits have been widely recognized.