What is the difference between metabolic acidosis and respiratory acidosis?

There is a difference between metabolic acidosis and respiratory acidosis. A common symptom of metabolic acidosis is acid-base imbalance, usually caused by lactic acidosis, that is, metabolic acidosis is the most common cause. Respiratory acidosis is usually caused by CO2 retention, and symptoms include difficulty breathing, blurred vision, irritability, etc. Many people still don’t understand the difference between metabolic acidosis and respiratory acidosis. Let’s take a look.

1. What is metabolic acidosis

Metabolic acidosis is the most common acid-base disorder, caused by an increase in extracellular fluid H+ or a loss of HCO3-, and is characterized by a primary decrease in HCO3- (<21mmol/L) and a decrease in pH (<7.35). In the clinical judgment of metabolic acidosis, the anion gap (AG) has important clinical value. According to different AG values, metabolic acidosis can be divided into high AG normal chloride type and normal AG high chloride type.

2. Causes of metabolic acidosis

High AG normochloric metabolic acidosis

Lactic acidosis Lactic acidosis is a common cause of metabolic acidosis. Normal lactic acid is formed by the hydrogenation of pyruvate by NADH under the action of lactate dehydrogenase (LDH), and NADH is converted into NAD. Lactate can also be converted to pyruvate when NAD is converted to NADH under the action of LDH. Therefore, the direction of the above reaction is mainly determined by the concentration of pyruvate and lactate as reaction substrates and the ratio of NADH and NAD. NADH can be produced during normal glucose fermentation, but the generated NADH can go to the mitochondria to generate NAD. In addition, pyruvate is converted into acetyl-CoA by the action of pyruvate dehydrogenase (PDH), which is then converted into CO2 and H2O through the tricarboxylic acid cycle.

The normal blood lactate level is very low, at 1 to 2 mmol/L. When it exceeds 4 mmol/L, it is called lactic acidosis. Lactic acidosis is clinically divided into two types: A and B.

3. Respiratory acidosis

Respiratory acidosis (acute respiratory acidosis) is often caused by CO2 retention. In the acute phase, the compensatory effect of the kidneys is not significant and the bicarbonate buffer system does not work, so acidosis progresses rapidly and can reach a severe level within a dozen minutes. Moreover, the retained CO2 can easily enter the cells, leading to intracellular acidosis. If not corrected in time, the mortality rate is very high. Its main characteristics are increased plasma PaCO2 and a compensatory increase in HCO3- levels in the chronic phase.

4. Common causes of respiratory acidosis

Respiratory center depressants, respiratory muscle weakness, upper airway obstruction, etc.

5. Common symptoms of respiratory acidosis

Shortness of breath, difficulty breathing, headache, blurred vision, irritability, etc.

6. Causes of respiratory acidosis

1. Respiratory center depressant drugs

Such as various sedatives or anesthetics.

2. Respiratory muscle or chest wall disorders

Such as respiratory muscle weakness, paralysis or restriction, insufficient ventilation or ventilation failure when using a ventilator, etc.

3. Upper airway obstruction

Acute tracheal foreign body, acute pharyngolaryngitis spasm, etc.

4. Lung disease

Such as chronic obstructive pulmonary disease, pulmonary edema, atelectasis, acute respiratory distress syndrome (ARDS), etc.

5. Others

Such as high fever or hyperthyroidism.

VII. Clinical manifestations

Acute severe respiratory acidosis is manifested by rapid breathing, dyspnea and obvious neurological symptoms, such as headache, blurred vision, irritability, and even tremors, confusion, delirium and coma. Physical examination may reveal optic disc edema, increased cerebrospinal fluid pressure, and cardiac arrhythmias. The symptoms of chronic respiratory acidosis are often masked by the primary disease.

8. Inspection

A blood gas analysis can diagnose respiratory acidosis based on decreased pH and increased PCO2.