Respiratory acidosis

Introduction Respiratory acidosis is characterized by a primary increase in plasma H 2 CO 3 concentration (the increase in PCO2 into the compensatory increase in HCO3, and the decrease in the arterial blood pH at the time of decompensation) increases the compensatory increase in HCO3. The increase in renal absorption of HCO3 is achieved, the compensation of the kidney is slow, the compensatory increase of HCO3 takes a certain time, and there is a certain limit on the increase of compensatory HCO3. Acute respiratory acidosis and chronic respiratory acid The compensatory increase of poisoned HCO3 is very different and shows different rules.

Cause

The main reason is the lowering of the ventilation function of the lungs, which is seen in respiratory obstruction, pneumonia, atelectasis, chest and abdomen surgery, trauma and so on.

an examination

(1) Medical history: The cause of respiratory acidosis can be central lesions, thoracic and respiratory muscle disorders, but the most common clinical manifestations are lung lesions. Therefore, attention should be paid to lung and related ventilatory dysfunction in the medical history. , the existence of disorders such as diffuse dysfunction of the lungs, ventilation and imbalance of blood flow, as well as history of smoking, asthma and so on. Respiratory acidosis must be produced on the basis of respiratory failure or respiratory insufficiency. Therefore, patients with respiratory acidosis have adequately mobilized or depleted their respiratory compensation and have experienced decompensation, dysfunction or failure.

(B) physical examination: In addition to respiratory diseases and respiratory function compensation symptoms, patients with severe respiratory acidosis often have a variety of neurological symptoms, such as headache, blurred vision, restlessness, irritability, further development to tremor , sputum and lethargy, coma (so-called carbon dioxide anesthesia). As acidemia causes cerebral vasodilation and increased cerebral blood flow, it can cause elevated cerebrospinal fluid pressure and papilledema. HCO3- in the blood is slow through the blood-brain barrier, and carbon dioxide can quickly cross the blood-brain barrier and reach equilibrium. Therefore, when acute hypercapnia, ie acute respiratory acidosis, the pH in the brain and cerebrospinal fluid is lower than that of chronic respiration. Acidosis is obvious, and the decrease of PH in brain and cerebrospinal fluid is greater than that of arterial blood. Therefore, neurological dysfunction in acute respiratory acidosis is more obvious than chronic respiratory acidosis and metabolic acidosis.

Respiratory acidosis often involves metabolic acidosis, and the combined arterial blood pH can be significantly reduced. For example, lowering to 7.10 or less often causes severe hypotension due to arrhythmia and peripheral vasodilation. At this time, the decrease in pH, that is, acidemia, weakens the contractile reactivity of blood vessels to catecholamines, so it is difficult to increase blood pressure by using a vasculature before the pH is restored to 7.15-7.20. Chronic respiratory acidosis often associated with pulmonary heart disease and systemic edema. However, cardiac output and glomerular filtration rate are often normal or near normal.

(3) Laboratory examination: blood gas analysis and examination can be diagnosed as respiratory acidosis according to PH reduction and PCO2 increase. However, respiratory acidosis can be mixed with metabolic acidosis and/or metabolic alkalosis, and simple respiratory acidosis is acute and chronic. The changes in blood gas analysis indicators of acute and chronic respiratory acidosis are different. In chronic respiratory acidosis, there are acute and chronic points. The changes in blood gas analysis indexes of acute and chronic respiratory acidosis are different. On the basis of chronic respiratory acidosis, acute respiratory acidosis can also be combined. Therefore, accurate identification of respiratory acidosis is more difficult to identify than metabolic acid-base disorders.

Differential diagnosis

There are 4 types of simple acid-base balance disorder, namely metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis.

First, respiratory alkalosis: respiratory alkalosis due to increased stress in the central and peripheral nervous system can cause a series of symptoms, including dizziness. The limbs and the area around the mouth are abnormal, muscle spasms, hands and feet, etc., may have swelling or pain in the chest. In addition, various supraventricular and ventricular arrhythmias can occur. Respiratory alkalosis can cause cerebral blood flow to decrease, and cerebral blood flow is also one of the causes of abnormal nervous system function. The experiment reported that when the PCO2 decreased by 2.6 kPa (20 mmHg), the cerebral blood flow could be reduced by 35%-40%. Abnormalities in nervous system function mainly occur in acute respiratory alkalosis, but rarely occur in chronic respiratory alkalosis.

Second, respiratory acidosis: In addition to the symptoms of respiratory diseases and respiratory function compensation, patients with severe respiratory acidosis often have a variety of neurological symptoms, such as headache, blurred vision, restlessness, irritability, further development to Tremors, paralysis and lethargy, coma (so-called carbon dioxide anesthesia). As acidemia causes cerebral vasodilation and increased cerebral blood flow, it can cause elevated cerebrospinal fluid pressure and papilledema. HCO3- in the blood is slow through the blood-brain barrier, and carbon dioxide can quickly cross the blood-brain barrier and reach equilibrium. Therefore, when acute hypercapnia, ie acute respiratory acidosis, the pH in the brain and cerebrospinal fluid is lower than that of chronic respiration. Acidosis is obvious, and the decrease of PH in brain and cerebrospinal fluid is greater than that of arterial blood. Therefore, neurological dysfunction in acute respiratory acidosis is more obvious than chronic respiratory acidosis and metabolic acidosis.

Respiratory acidosis often involves metabolic acidosis, and the combined arterial blood pH can be significantly reduced. For example, lowering to 7.10 or less often causes severe hypotension due to arrhythmia and peripheral vasodilation. At this time, the decrease in pH, that is, acidemia, weakens the contractile reactivity of blood vessels to catecholamines, so it is difficult to increase blood pressure by using a vasculature before the pH is restored to 7.15-7.20. Chronic respiratory acidosis often associated with pulmonary heart disease and systemic edema. However, cardiac output and glomerular filtration rate are often normal or near normal.

Third, metabolic alkalosis: severe metabolic alkalosis can cause functional abnormalities in the peripheral nerves of the central, such as abnormalities, muscle spasms, headaches, irritability. Ankle and disturbance of consciousness, the above-mentioned abnormalities of central nervous function are obvious in patients with alkalosis after hypercapnia, because patients with chronic hypercapnia, increased PaCO2, and increased compensatory HCO3- in plasma and cerebrospinal fluid, when mechanical ventilation is applied After treatment, PCO2 decreased rapidly, and HCO3- could not quickly pass through the blood-brain barrier, resulting in a sudden increase in the pH of the cerebrospinal fluid. Therefore, the speed of correcting chronic respiratory acidosis should not be too fast.

4. Metabolic acidosis: Respiratory activity is a compensatory response of the body during acidosis. Examination can reveal that the breathing is deep and fast, and the ventilation per minute can be increased by 4-8 times, even if the patient feels difficulty breathing or respiratory distress. In the case of acidemia, the peripheral blood vessels dilate, so the facial skin is flushed. As cardiovascular susceptibility to catecholamines is reduced, ventricular function is reduced, myocardial contractility is reduced, blood pressure is reduced, and even shock occurs. If a ventricular arrhythmia occurs, the pulse and electrocardiogram will respond. Generally, it is considered that the occurrence of ventricular arrhythmia in acidemia is related to hyperkalemia. In acidemia, anorexia and nausea can cause weight loss, and the nervous system is mild and weak, and severe cases can cause drowsiness and coma. Long-term or recurrent acidosis can cause various bone diseases. In children, it can affect the growth and development of the body, and even fibrosis and rickets, and osteomalacia or osteoporosis occurs in adulthood. Henderson's test: For patients with deep, fast, and suspected metabolic acidosis, stop breathing and stop breathing as a breath holding. If the breath holding time is less than 20 seconds, it is a virtue. The pine test was positive. This positive generally indicates that the patient is in a severe or severe metabolic acidosis state because the HCO3- is reduced, the pH is lowered, the respiratory center excitability is enhanced, respiratory activity is enhanced, and H2CO3 compensatory discharge is increased.

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