What is Acidosis?
Acidosis is a change in the acid-base balance of an organism as a result of insufficient excretion and oxidation of organic acids (for example, beta-butyric acid). Usually these products are quickly removed from the body. In febrile diseases, intestinal disorders, pregnancy, fasting, etc., they are retained in the body, which is manifested in mild cases by the appearance in the urine of acetoacetic acid and acetone (so-called acetonuria), and in severe cases (for example, diabetes mellitus) can result to coma.
Causes of Acidosis
Usually, oxidation products of organic acids are quickly removed from the body. In febrile diseases, intestinal disorders, pregnancy, fasting, etc., they are retained in the body, which is manifested in mild cases by the appearance in the urine of acetoacetic acid and acetone (so-called acetonuria), and in severe cases (for example, diabetes mellitus) can result to coma.
Pathogenesis during Acidosis
According to the mechanisms of occurrence, there are 4 types of violations of the acid-base state, each of which can be compensated and decompensated:
- non-respiratory (metabolic) acidosis;
- respiratory acidosis;
- non-respiratory (metabolic) alkalosis;
- respiratory alkalosis.
Non-respiratory (metabolic) acidosis is the most common and most severe form of acid-baseline impairment. The basis of non-respiratory (metabolic) acidosis is the accumulation in the blood of so-called non-volatile acids (lactic acid, hydroxybutyric, acetoacetic, etc.) or the loss of buffer bases by the body.
Symptoms of Acidosis
The main symptoms of acidosis are often masked by the manifestations of the underlying disease or are difficult to distinguish from them. Mild acidosis can be asymptomatic or accompanied by some fatigue, nausea and vomiting. Severe metabolic acidosis (for example, pH is less than 7.2 and the concentration of bicarbonate ions is less than 10 meq / l) is most characteristic of hyperpnea, manifested by an increase in the depth first, and then the respiration rate (Kussmaul breathing). There may be signs of a decrease in ECG, especially in diabetic acidosis or loss of base through the gastrointestinal tract. Severe acidosis sometimes leads to circulatory shock due to impaired myocardial contractility and the reaction of peripheral vessels to catecholamines, as well as to an increasing stupor.
Diagnosis of Acidosis
In severe acidosis, when the content of bicarbonate ions in the plasma becomes very low, urine pH drops below 5.5, blood pH drops below 7.35, HCO3 concentration falls below 21 meq / l. In the absence of pulmonary diseases, the partial pressure of carbon dioxide in arterial blood does not reach 40 mm Hg. Art. With simple metabolic acidosis, it can decrease by about 1-1.3 mm Hg. Art. for each mEq / l reduction in plasma HCO3 level. A greater incidence of pCO2 indicates simultaneous primary respiratory alkalosis.
Many forms of metabolic acidosis are characterized by an increase in undeterminable anions. The number of undetectable serum anions (sometimes called the anion interval or anion deficiency) is estimated by the difference between the serum sodium concentration and the sum of chloride and bicarbonate concentrations. It is considered that in normal this value varies within 12 + 4 mEq / l. However, it was obtained by measuring electrolyte levels using the Technicon autoanalyzer, which was widely used in the 1970s. At the present time, most clinical laboratories use other techniques that give slightly different numbers. In particular, the normal level of chloride in the serum is higher, and the undetectable anions are normally less – only 3-6 meq / l. You should be aware of this and proceed from the boundaries of the norms established in the laboratory whose services are used in this particular case.
Metabolic acidosis can be associated with the accumulation of undetectable anions — for example, sulfate in renal failure, ketone bodies in diabetic or alcoholic ketoacidosis, lactate, or exogenous toxic substances (ethylene glycol, salicylates). Metabolic acidosis with a normal amount of undetectable anions (hyperchloremic metabolic acidosis) is usually caused by a primary loss of bicarbonate through the gastrointestinal tract or kidney (for example, in renal canalicular acidosis).
Diabetic acidosis is usually characterized by hyperglycemia and ketonemia. With hyperglycemia and non-ketone (according to the usual clinical analyzes) acidosis, the content of lactic and / or p-hydroxybutyric acid in the blood is increased.
Ethylene glycol poisoning should be suspected in case of unexplained acidosis if oxalate crystals are present in the urine.
Salicylate poisoning is characterized initially by respiratory alkalosis and then metabolic acidosis; the level of salicylates in the blood usually exceeds 30-40 mg%.
Since acidosis is often accompanied by hypovolemia, mild azotemia is often noted (blood urea nitrogen content is 30-60 mg%). A more significant increase in blood urea nitrogen levels, especially in combination with hypocalcemia and hyperphosphatemia, indicates renal failure as a cause of acidosis. Hypocalcemia is sometimes observed in septic shock. Changes in the level of potassium in serum during acidosis were discussed above (see on violations of potassium metabolism). In lactic acidosis, hyperkalemia is relatively rare, unless there is at the same time no kidney failure and / or increased tissue breakdown.
Elimination of the cause of acidosis (for example, insulin deficiency in diabetes), as well as symptomatic – ingestion of soda, plenty of drink.