What Is Refractory Hypoxemia?

Hypoxemia refers to the lack of oxygen in the blood, and the arterial oxygen partial pressure (PaO ₂ ) is lower than the normal lower limit of the same age, which is mainly manifested by the decrease in partial oxygen pressure and blood oxygen saturation. Adult normal arterial blood oxygen pressure (PaO ₂ ): 83-108 mmHg. Hypoxia can be caused by various reasons such as central nervous system disorders, bronchial and pulmonary lesions that cause ventilation and / or ventilation dysfunction. Due to the different degrees, speed and duration of hypoxemia, the effects on the body are also different. Hypoxemia is one of the common critical illnesses in the respiratory department and one of the important clinical manifestations of respiratory failure.

Basic Information

English name

hypoxemia; mionecticblood

Visiting department

Internal medicine

Common symptoms

Partial blood oxygen pressure, blood oxygen saturation decreases

Contagious

no

Causes of hypoxemia

The common causes of hypoxemia are: low inhaled oxygen partial pressure; inadequate alveolar ventilation; diffuse dysfunction; alveolar ventilation / blood flow imbalance; right-to-left shunt.

Hypoxemia diagnosis

1. PaO _{2 is} reduced due to the low oxygen pressure diffused into the arterial blood. Too low PaO ₂ can directly cause the decrease of CaO ₂ and SaO ₂ .

2. If there is no abnormal change in the quality and quantity of Hb, CO ₂ max is normal.

3. As PaO ₂ decreases, 2,3-DPG in red blood cells increases, so blood SaO ₂ decreases.

4. During hypotonic hypoxia, the decrease of PaO ₂ and blood SaO ₂ reduces CaO ₂ .

5. The arterio-venous oxygen difference decreases or changes little. Usually about 5ml of oxygen is used when 100ml of blood flows through the tissue, that is, A-VdO ₂ is about 2.23mmol / L (5ml / dl). The motive force for the diffusion of oxygen from the blood to the tissue is the oxygen partial pressure difference between the two. When hypotonic hypoxia, PaO ₂ and CaO _{2 are} significantly reduced, which slows down the diffusion rate of oxygen and the same amount of blood diffuses to Tissue oxygen is reduced, which ultimately leads to a decrease in A-VdO ₂ and tissue hypoxia. In the case of chronic hypoxia, the change in A-VdO ₂ may not be noticeable when the tissue's ability to use oxygen is compensated.

6. Changes in skin and mucous membrane color: The average concentration of deoxygenated Hb in normal capillaries is 26 g / L (2.6 g / dl). During hypotonic hypoxia, the oxygenated Hb concentration in arterial blood and venous blood is reduced, the oxygenated Hb concentration in capillaries is necessarily reduced, and the deoxygenated Hb concentration is increased. When the average concentration of deoxygenated Hb in capillaries increases to more than 50g / L (5g / dl) (SaO ₂ 80% to 85%), the skin and mucous membranes can appear blue and purple, which is called cyanosis. Hair cyanosis is prone to occur in chronic hypotonic hypoxia. Hair cyanosis is a manifestation of hypoxia, but patients with hypoxia may not always have cyanosis. Similarly, patients with cyanosis can also be free of hypoxia, such as patients with polycythemia vera, due to abnormal increase in Hb, the deoxygenated Hb content in capillaries can easily exceed 50g / L, so cyanosis is easy to occur without hypoxia symptoms.

Hypoxemia treatment

Oxygen therapy

Includes simple mask, invasive mechanical ventilation, non-invasive mechanical ventilation. The purpose of oxygen therapy is to improve the arterial blood oxygen pressure, oxygen saturation and oxygen content to correct hypoxemia, ensure oxygen supply to the tissue, and achieve the purpose of alleviating tissue hypoxia. Whatever the underlying disease is, it is an indication of oxygen therapy. From the perspective of the oxygen dissociation curve, PaO _{2 is} lower than 8.0 kPa (60 mmHg), which indicates that it is on the verge of decompensation. A slight decrease in PaO ₂ will cause a significant decrease in oxygen saturation. According to blood gas analysis, hypoxemia is divided into two types. Hypoxemia with hypercapnia: Hypoxia caused by inadequate ventilation and carbon dioxide retention. Oxygen therapy can correct hypoxemia, but it does not help the discharge of carbon dioxide. If improperly applied, it can worsen carbon dioxide retention. Simple hypoxemia: Generally caused by diffuse dysfunction and imbalance of ventilation / blood flow. Diffuse dysfunction. By increasing the concentration of inhaled oxygen, hypoxemia can be corrected more satisfactorily. However, the intrapulmonary shunt caused by imbalance of ventilation / blood flow is not ideal because oxygen therapy produces unvented alveoli Arteriovenous shunting does not help.

2. Hyperbaric oxygen chamber treatment

3. relieve bronchospasm

Phosphodiesterase inhibitors such as aminophylline and dihydroxyprophylline are used to relax airway smooth muscle and inhibit histamine release. It is best to monitor heart rate, heart rate, and blood concentration while taking the medication. Other anticholinergic drugs such as ipratropine, selective 2 receptor agonists such as salbutanol, and adrenal corticosteroids are also available.