Decreased arterial oxygen saturation

Introduction Oxygen saturation (SO2) is the percentage of oxygen-bound oxyhemoglobin (HbO2) in the blood that accounts for the total capacity of the combined hemoglobin (Hb), which is the concentration of blood oxygen in the blood. It is an important physiological part 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 oxygen and hemoglobin. Therefore, monitoring arterial oxygen saturation (SaO2) can estimate lung oxygenation and hemoglobin oxygen carrying capacity. The blood oxygen saturation of normal human arterial blood is 98%.

Cause

In hypoxic hypoxemia, hemoglobin is not fully effective due to insufficient supply of oxygen. At this time, the partial pressure of blood oxygen is lowered and the oxygen saturation is low. For example, in chronic heart and lung disease, if SaO2 is lowered, it is oxygen supply. Insufficient performance; if there is no environmental factor of hypoxia, it is the result of lung ventilation and ventilation disorder. If hypoxemia, the oxygen partial pressure is reduced and SaO2 is not low, suggesting hemoglobin deficiency or abnormal hemoglobinemia.

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Many clinical diseases cause a lack of oxygen supply, which will directly affect the normal metabolism of cells, and will seriously threaten human life. Therefore, real-time monitoring of arterial 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 the blood gas analyzer to perform electrochemical analysis, and measure the hemorrhagic oxygen partial pressure PO2 to calculate the hemorrhage oxygen saturation. This method is cumbersome and cannot be continuously monitored.

The current measurement method is to use a finger-type photoelectric sensor. When measuring, it is only necessary to put the sensor on the human finger, using a finger as a transparent container for hemoglobin, using red light with a wavelength of 660 nm and near-infrared light of 940 nm as an incident light source. The light transmission intensity through the tissue bed is measured to calculate the hemoglobin concentration and blood oxygen saturation, and the instrument can display the blood oxygen saturation of the human body, thereby providing a continuous non-invasive blood oxygen measuring instrument for clinical practice.

Differential diagnosis

First, arterial oxygen partial pressure (PaO2):

Refers to the pressure generated by the physical dissolution of oxygen molecules in the blood. Healthy people PaO2 gradually decrease with age, and physiological effects such as receptor level. According to the relationship between oxygen partial pressure and blood oxygen saturation, the dissociation curve of oxyhemoglobin is in S form. When PaO2>8kPa (60mmHg) or more, the curve is flat, the oxygen saturation is above 90%, and PaO2 is changed by 5.3kPa (40mmHg). ), and the blood oxygen saturation changes little, indicating that the oxygen partial pressure is far more sensitive than oxygen saturation; but when PaO2 <8kPa or less, the curve is steep and straight, the oxygen partial pressure drops slightly, and the blood oxygen saturation drops sharply. PaO2 is less than 8 kPa (60 mmHg) as a diagnostic indicator of respiratory failure.

Second, arterial oxygen saturation (SaO2):

Is the oxygen percentage of the unit hemoglobin, the normal value is 97%. When PaO2 is lower than 8kPa (60mmHg), the hemoglobin oxygen dissociation curve is in the steep section, the oxygen saturation reflects the hypoxic state, so in the case of severe respiratory failure, the pulse oximeter is used to help evaluate In the absence of O2, adjusting the concentration of O2 to make the patient's SaO2 reach more than 90%, in order to reduce the blood gas analysis of traumatic arterial blood, which plays a positive role in rational oxygen therapy and assessment of curative effect.

Third, arterial blood oxygen content (CaO2):

It is the number of milliliters of oxygen in 100 ml of blood. These include the sum of hemoglobin binding oxygen and physically dissolved oxygen in plasma. CaO2 = 1.34 × SaO2 × Hb + 0.003 × PaO2. The reference value of CaO2 in healthy persons was 20 ml%. The mixed venous blood oxygen saturation (SVO2) is 75%, and the oxygen content CVO2 is 15 ml%. About 100 ml of oxygen per 100 ml of arterial blood is used for tissue utilization. Hemoglobin is reduced, SaO2 is lower than normal, and blood oxygen content is still in the normal range.

Fourth, arterial blood carbon dioxide partial pressure (PaCO2):

Refers to the pressure generated by physically dissolved CO2 molecules in the blood. Normal PaCO2 is 4.6 kPa-6 kPa (35-45 mmHg), greater than 6 kPa is insufficient ventilation, and less than 4.6 kPa may be excessive ventilation. Insufficient acute ventilation, when PaCO2>6.6kPa (50mmHg), according to the Henderson-Hassellbalch formula, the pH is below 7.20, which will affect circulation and cell metabolism. Chronic respiratory failure due to the body compensation mechanism, PaCO2>6.65kPa (50mmHg) as a diagnostic indicator of respiratory failure.

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