Acidosis

This is an increase in the acidity of body fluids (decrease in pH, excess of acids in the body). In the case of acidosis, the concentration of hydrogen ions in the blood is higher than normal (pH < 7.37). When the pH drops below 6.8, death occurs. Changes in the acid-base balance, both acidosis and alkalosis, are caused by respiratory disorders, metabolic factors, etc. Respiratory acidosis begins with a decrease in the minute volume of the lungs (e.g., bronchial asthma, emphysema, asphyxia, etc.). During all these disorders, there is hypoventilation and hypercapnia (increased pCO₂ in arterial blood). As a result, the concentration of H₂CO₃ in the plasma increases. Increased pCO₂, acting on the buffering mechanism of hemoglobin, increases the concentration of HCO₃^– ions in the plasma. In the case of lung hypoventilation, the patient’s blood pH rapidly decreases and the levels of H₂CO₃ and HCO₃^– increase. One of the main causes of respiratory acidosis is lung hypoventilation (e.g., bronchiolar spasms or airway obstruction). Bronchiolar spasms are caused by increased acetylcholine release in nerve endings or increased sensitivity of choline receptors to acetylcholine during hyperallergic reactions (anaphylaxis). The danger of bronchiolar spasms during acidosis is that it creates the possibility of forming a pathogenic cycle:

In cases of prolonged increase in pCO₂ and hyperkalemia, long-term hypercapnia and hyperkalemia may occur. Respiratory acidosis causes dilation of brain arterioles, leading to cerebral arterial hyperemia and increased intracranial pressure. The reason for this is long-term hypercapnia and hyperkalemia. The secretion of ammonium salts with urine increases in such patients. Metabolic acidosis is the most common and severe disturbance of the acid-base balance. During metabolic acidosis, organic acids accumulate in tissues and blood. This acidosis begins with a disruption in metabolism. Metabolic acidosis can occur during diabetes mellitus, fasting, fever, gastrointestinal diseases, shock (cardiogenic, traumatic, burn, etc.). Metabolic acidosis is particularly pronounced in severe forms of diabetes and when insulin is not used. Blood acidity is determined by large amounts of ketone bodies (b-hydroxybutyrate, acetoacetate) entering the blood. As a compensation in the body, H₂CO₃ decreases because CO₂ is excreted through the lungs. In severe forms of diabetes, acidosis is compensated by the excretion of very large amounts of CO₂ through the lungs, with low concentrations of H₂CO₃ and HCO₃^–, reducing the blood buffering capacity. This is dangerous for the body. The clinical picture of metabolic acidosis is related to the underlying disease. When blood pH drops below 7.2, the amount of blood ejected by the heart decreases, sometimes resistance to the vasoconstrictive effect of catecholamines is detected, and arterial hypotension is possible. In the human body, during metabolism, acidic products are formed about 20 times more than basic ones, so systems that neutralize these products prevail in the body.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė