The common causes of hypoxemia are: ① low partial pressure of inhaled oxygen; ② Alveolar ventilation Insufficient; ③ Diffusion dysfunction; ④ Alveolar ventilation/blood flow imbalance; ⑤ Right to left shunt 。 1. Due to diffusion Arterial blood Low oxygen pressure in makes PaO two Lower, too low PaO two Can directly cause CaO two And SaO two Lower. 2. If Hb has no abnormal changes in quality and quantity, CO two Max is normal.
3. Due to PaO two When lowering, red blood cell Increased internal 2,3-DPG, so blood SaO two Lower. four Hypotonic hypoxia PaO two And blood SaO two Reduce CaO two Lower. 5. Arteriovenous oxygen difference decreases or changes little. Usually, when 100ml of blood flows through tissues, about 5ml of oxygen is used, namely A-VdO two It is about 2.23mmol/L (5ml/dl). The power of oxygen diffusion from blood to tissue is between the two Oxygen partial pressure Poor, PaO in case of hypotonic hypoxia two Significantly lower and CaO two Significantly reduce the oxygen content Dispersion velocity Slowing down, the amount of oxygen diffused by the same amount of blood to the tissue decreases, eventually leading to A-VdO two Decrease and tissue hypoxia. In case of chronic hypoxia, A-VdO two The change may not be obvious. six Skin mucosa Color change: normal blood capillary The average concentration of deoxygenated Hb is 26g/L (2.6g/dl). During hypotonic hypoxia, arterial blood and veinal blood Of Oxygenation The concentration of Hb decreases, the oxygenated Hb in capillaries inevitably decreases, and the concentration of deoxygenated Hb increases. When deoxygenated Hb in capillaries is average Concentration increase To more than 50g/L (5g/dl) (SaO two ≤ 80%~85%) can make skin and mucosa appear cyan, which is called Cyanosis 。 Cyanosis is easy to occur in chronic hypotonic hypoxia. Cyanosis is a manifestation of hypoxia, but not all patients with hypoxia may have cyanosis. Similarly, patients with cyanosis may also have no hypoxia, such as Polycythemia vera In patients, due to the abnormal increase of Hb, the content of deoxygenated Hb in capillaries is very easy to exceed 50g/L, so cyanosis is easy to occur Anoxic symptom 。 Including simple mask, invasive mechanical ventilation , non-invasive mechanical ventilation. The purpose of oxygen therapy is to improve Arterial partial pressure of oxygen 、 Oxygen saturation and oxygen content In order to correct hypoxemia, ensure the oxygen supply to the tissue, and achieve the purpose of alleviating tissue hypoxia. Regardless of its Basic diseases Which is it? It is the indication of oxygen therapy. from Oxygen dissociation curve Look, PaO two If it is lower than 8.0kPa (60mmHg), it indicates that it is on the edge of decompensation, PaO two A slight decrease will result in a significant decrease in oxygen saturation. Press Blood gas analysis Hypoxemia can be divided into two types. ① Hypoxemia with Hypercapnia ： Hypoventilation Induced hypoxia, with carbon dioxide Retention, oxygen therapy can correct hypoxemia, but it is not conducive to the discharge of carbon dioxide. If not properly applied, it can aggravate Carbon dioxide retention 。② Simple hypoxemia: generally diffusion dysfunction And ventilation/blood flow imbalance. Diffusion dysfunction can satisfactorily correct hypoxemia by increasing the concentration of inhaled oxygen, but it is caused by the imbalance of ventilation/blood flow ratio intrapulmonary shunt , oxygen therapy is not ideal, because oxygen therapy is not good for ventilatory Alveoli Resulting Arteriovenous shunt No help. 3. Cancellation Bronchospasm 
