Respiratory alkalosis

Introduction Respiratory alkalosis refers to a decrease in plasma H 2 CO 3 concentration or PaCO 2 due to excessive lung ventilation, resulting in an increase in pH (>7.45). According to the incidence of the disease, it is divided into two categories: acute and chronic. In the acute case, the PaCO 2 decreased by 10 mmHg (1.3 kPa), the HCO 3 decreased by about 2 mmol/L, and the chronic HCO 3 decreased to 4-5 mmol/L. Respiratory alkalosis occurs within 6 hours, and when the kidney still shows significant compensatory function, it is called acute respiratory alkalosis. After 6 to 18 hours of respiratory alkalosis, when the kidney has shown compensatory function, it is called persistent respiratory alkalosis, or chronic respiratory alkalosis.

Cause

Mental hyperventilation

Common causes of respiratory alkalosis. In severe cases, you may have dizziness, abnormal feelings, and occasional paralysis. Common in patients with rickets.

2. Metabolic process abnormalities

When the thyroid function is hyperthyroidism and fever, the ventilation can be significantly increased beyond the amount of CO2 that should be discharged. Can cause respiratory alkalosis, but generally not serious. Excessive ventilation at this time may be caused by an increase in pulmonary blood flow through a reflective response.

3. Hypoxia hypoxia

Hyperventilation during hypoxic hypoxia is a compensation for hypoxia, but at the same time it can cause excessive CO2 excretion and respiratory alkalosis. Common in people who enter the plateau, mountains or high altitudes. Thoracic and pulmonary lesions such as pneumonia, pulmonary embolism, pneumothorax, pulmonary congestion, etc. cause thoracic, pulmonary vascular or lung tissue afferent nerve stimulation and increased reflex ventilation. In addition, in some patients with congenital heart disease, hyperventilation can also occur due to increased right-to-left shunt.

4. Central nervous system disorders

Encephalitis, meningitis, brain tumors, cerebrovascular accidents, and respiratory center of patients with craniocerebral injury are stimulated and excited, and hyperventilation occurs.

5. Salicylic acidosis

Salicylic acid can directly stimulate the respiratory center to increase its excitability and increase sensitivity to normal stimuli. Thus hyperventilation occurs.

6. Gram-negative bacilli sepsis

In patients with Gram-negative bacilli entering the bloodstream, significant hyperventilation can occur when the body temperature and blood pressure have not changed. Pco2 has as low as 17mmHg. This change is very helpful for diagnosis.

7. Excessive artificial respiration.

8. Cirrhosis

Hyperventilation may occur in patients with cirrhosis with ascites and elevated blood NH3. May be caused by the stimulating effect of NH3 on the respiratory center.

9. Metabolic acidosis

Suddenly corrected, for example, using NaHCO3 to correct metabolic acidosis, the concentration of extracellular fluid [HCO3-] rapidly rose to normal, but the blood-brain barrier was very slow. At this time, the brain was still metabolic acidosis, so hyperventilation still persisted. .

Pregnancy

There is a moderate increase in ventilation during pregnancy, and it is currently believed that progesterone stimulates the respiratory center, and some synthetic progesterone preparations also have this effect. During the pregnancy reaction period, ketoacidosis may occur due to vomiting and insufficient diet. Respiratory alkalosis may occur after the pregnancy reaction period, sometimes causing hand and foot convulsions.

an examination

1. Blood gas analysis and detection.

2. Detection of electrolyte sodium, potassium, calcium, chlorine and magnesium.

3. Liver and kidney function tests.

According to the condition and clinical symptoms, choose ECG, B-ultrasound, X-ray examination and so on.

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 can cause a range of symptoms, including dizziness, due to increased stress in the central and peripheral nervous systems. The limbs and the area around the mouth are abnormal, muscle spasms, convulsions of the 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 (The 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 nervous system, such as paresthesia, muscle spasms, headaches, and 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.

Fourth, metabolic acidosis

Respiratory activity is a compensatory response to the body during acidemia. 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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