The metabolic process of the human body is a biological oxidation process, and the oxygen required in the metabolic process enters the human blood through the respiratory system, combines with hemoglobin (Hb) in the red blood cells to form oxyhemoglobin (HbO2), and then transports it to all parts of the body. Part of the tissue cells go.
Blood oxygen saturation (SO2) is the percentage of the volume of oxyhemoglobin (HbO2) that is bound by oxygen in the blood to the total volume of hemoglobin (Hb) that can be bound, that is, the concentration of blood oxygen in the blood. It is an important physiology of the respiratory cycle parameter. The functional oxygen saturation is the ratio of HbO2 concentration to HbO2+Hb concentration, which is different from the percentage of oxygenated hemoglobin. Therefore, monitoring arterial oxygen saturation (SaO2) can estimate the oxygenation of the lungs and the ability of hemoglobin to carry oxygen. Normal human arterial blood oxygen saturation is 98%, and venous blood is 75%.
(Hb stands for hemoglobin, hemoglobin, abbreviated Hb)
Measurement methods
Many clinical diseases will cause the lack of oxygen supply, which will directly affect the normal metabolism of cells, and seriously threaten human life. Therefore, real-time monitoring of arterial blood oxygen concentration is very important in clinical rescue.
The traditional blood oxygen saturation measurement method is to first collect blood from the human body, and then use a blood gas analyzer for electrochemical analysis to measure the partial pressure of blood oxygen PO2 to calculate the blood oxygen saturation. This method is cumbersome and cannot be continuously monitored.
The current measurement method is to use a finger sleeve photoelectric sensor. When measuring, you only need to put the sensor on a human finger, use the finger as a transparent container for hemoglobin, and use red light with a wavelength of 660 nm and near-infrared light with a wavelength of 940 nm as the radiation. Enter the light source and measure the intensity of light transmission through the tissue bed to calculate the hemoglobin concentration and blood oxygen saturation. The instrument can display the human blood oxygen saturation, providing a continuous non-invasive blood oxygen measurement instrument for the clinic.
Reference value and meaning
It is generally believed that SpO2 should not be less than 94% normally, and that less than 94% is insufficient oxygen supply. Some scholars set SpO2<90% as the standard of hypoxemia, and believe that when SpO2 is higher than 70%, the accuracy can reach ±2%, and when SpO2 is lower than 70%, there may be errors. In clinical practice, we have compared the SpO2 value of several patients with the arterial blood oxygen saturation value. We believe that the SpO2 reading can reflect the patient’s respiratory function and reflect the change of arterial blood oxygen to a certain extent. After thoracic surgery, except for individual cases where the clinical symptoms and values do not match, blood gas analysis is required. The routine application of pulse oximetry monitoring can provide meaningful indicators for clinical observation of changes in the disease, avoiding repeated blood sampling for patients and reducing nurses’ The workload is worth promoting. Clinically, it is generally more than 90%. Of course, it needs to be in different departments.
Judgment, harm, and disposal of hypoxia
Hypoxia is an imbalance between the body’s oxygen supply and oxygen consumption, that is, tissue cell metabolism is in a state of hypoxia. Whether the body is hypoxic or not depends on whether the amount of oxygen transport and oxygen reserves received by each tissue can meet the needs of aerobic metabolism. The harm of hypoxia is related to the degree, rate and duration of hypoxia. Severe hypoxemia is a common cause of death from anesthesia, accounting for about 1/3 to 2/3 of death from cardiac arrest or severe brain cell damage.
Clinically, any PaO2<80mmHg means hypoxia, and <60mmHg means hypoxemia. PaO2 is 50-60mmHg called mild hypoxemia; PaO2 is 30-49mmHg called moderate hypoxemia; PaO2<30mmHg is called severe hypoxemia. The patient’s blood oxygen saturation under orthopedic respiration, nasal cannula and mask oxygenation was only 64-68% (approximately equivalent to PaO2 30mmHg), which was basically equivalent to severe hypoxemia.
Hypoxia has a huge impact on the body. Such as the influence on CNS, liver and kidney function. The first thing that occurs in hypoxia is the compensatory acceleration of the heart rate, the increase in heart beat and cardiac output, and the circulatory system compensates for the lack of oxygen content with a high dynamic state. At the same time, redistribution of blood flow occurs, and the brain and coronary blood vessels are selectively expanded to ensure adequate blood supply. However, in severe hypoxic conditions, due to the accumulation of subendocardial lactic acid, ATP synthesis is reduced, and myocardial inhibition is produced, leading to bradycardia, pre-contraction, blood pressure and cardiac output, as well as ventricular fibrillation and other arrhythmias Even stop.
In addition, hypoxia and the patient’s own disease may have an important impact on the patient’s homeostasis.
Post time: Oct-12-2020