Metabolic acidosis - SpeedyLook encyclopedia

The metabolic acidosis is a disorder of acido-basic balance defines by a fall of pH in the extracellular sector plasma tick.

Physiopathology

The intracellular pH at the Man is of 7,2, the extracellular pH of 7,4. These values are extremely closely controlled via several mechanisms based on the following equation: H⁺ + HCO₃^- <-> H₂CO₃ <-> H₂O + CO₂.

the pulmonary plug makes it possible to eliminate an excess from Acide by hyperventilation (Dyspnée of Kussmaul: Breathing full, major, making it possible to reject of CO₂ and the steam and thus to make increase the pH.)
the Rein S has two IMPORTANT functions:

to eliminate the H⁺ ions in the urines (excretion on the level of the distal circumvented tube) for 75% in the form of ammonium NH4⁺ (i.e. H⁺ + ammonia), the last quarter being eliminated in free form or in the form of other acids (for example H₂PO₄).

to reabsorb the H₂CO₃ bases, via the tube circumvented proximal in the cortical renal one.

The physiological standards at the human being are:

pH : between 7,38 and 7,42.
Bases : HCO₃^- = 26 mmol/L
pCO₂ (partial pressure in Carbon dioxide in the Blood) = 40 anion MmHg
Hole (difference between the acids and the bases in plasma i.e. Na⁺ + K⁺ - + Cl^-, normally located between 12 and 18.

The metabolic acidosis is defined by a fall of the pH under 7,38, that it that is the reason and the compensation mechanisms.

Diagnosis

The clinical signs of the acidosis are in rule discrete: one finds has minimum a full dyspnea of Kussmaul (compensation hyperventilation), the diagnosis is then confirmed by the measurement of the Gaz of blood. The major acidoses are often responsible for neurological disorders energy of mental confusion to the Coma. The clinical signs revealing of an etiology are to be sought with the patient or his entourage if this one is unconscious.

Etiology

The diagnosis etiologic rests on a fundamental examination to require at the same time as gases of blood: the blood Ionogramme, which makes it possible to calculate the anion hole, which only makes it possible to make the difference between an acidosis by excess of acid or loss in bases. The anion hole is calculated by difference between the cations and the anions in plasma: Na⁺ + K⁺ - + Cl^-.

Metabolic acidosis with high anion hole

The rise in the anion hole testifies to the presence in the blood of an acid which can be endogenous or exogenic (by intoxication)

Endogenous excess of acid

Lactic acidosis: it must generally with a severe Hypoxie tissue (states of shock, intoxication with the Carbon monoxide) but can also be due to certain intoxications (Biguanide S, in particular at insufficient renal, hepatic the or cardiac one), Cancer S, etc
Acido-ketosis: in the Diabetes sweetened insulinopenic very unbalanced, by accumulation of ketonic bodies.

Exogenic intoxications

Most frequent are the intoxication with the Aspirine, the Méthanol, the ethylene glycol.

Metabolic acidosises with normal anion hole

They are due to a loss excessive of bases: digestive losses (Diarrhea S acute) or renal losses (renal tubular Acidosis).

Treatment

Treatment etiologic (of the cause), when it is possible, is fundamental: assumption of responsibility of a state of shock, insulin treatment in the event of Acidocétose, etc

Of an acute metabolic acidosis

Dialysis (or extra-renal purification)

It is indicated in the event of acidosis due to a Toxique dialysable (for example an intoxication with the Biguanide S), in the event of Hyperkaliémie severe associated (the acidosis involves a hyperkaliemy), or in the event of oligo-anurie (less than 500 ml of Urine produced per day, which prevents a natural elimination of the accumulated acids). If extra-renal purification is not quickly available, an intravenous bicarbonate contribution must be considered.

Sodium intravenous bicarbonate contribution

This treatment must be held with the mineral metabolic acidosises, i.e. those which translate a defect of the normal metabolic acid excretion. In the event of organic metabolic acidosis (lactic acidosis, acido ketosis), the treatment must rest on the treatment of the cause. Indeed, the metabolisation of salts of organic acid in excess induced by the treatment of the cause is at the origin of a équimolaire generation of bicarbonate which thus corrects spontaneously the disorder. When the sodium bicarbonate is used, it owes the being with a greatest caution: many side effects indeed are risked when the pH is corrected too quickly or that the bicarbonates are brought back to their normal state: it is necessary to aim at a subnormal concentration in HCO₃^-, about 16 mmol/L after 6 hours of treatment. The risks are mainly due to the time which exists between the correction of the acidosis and the catch in compten of this correction by the Cerveau: indeed, the cerebral chemical receivers responsible for hyperventilation are stimulated by the pH of the céphalo-rachidian Liquide, of which the pH longer takes to be corrected than the blood pH. In the event of too fast standardization, one thus risks a respiratory Alcalose (the other risks are the Hypokaliémie, and the hydro-containing soda overload). Moreover, the sodium bicarbonate contribution can worsen the acidosis intacellulaire paradoxically by generating CO2 which diffuses freely in cellular space.

Of a chronic and moderate metabolic acidosis

The two major causes of chronic metabolic acidosis are the Impaired renal function (the Rein does not manage any more to remove the organization from its nitrogenized waste) and the renal tubular Acidose. The treatment rests on the sodium per-bone bicarbonate contribution to the long course, by water of Vichy or masterly preparation, from approximately 2 to 8 grams per day of HCO₃^-, with a regular monitoring of the blood ionogramme, urinary ionogramme, and gases of blood.

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