Metabolic Alcalose

The metabolic alcalose is a disorder of the acido-basic balance defined by a rise of pH in the extracellular sector plasma tick.

Physiopathology

Is the intracellular pH at the man of 7 (or 7.2?), 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, allowing to reject of CO₂ and the steam and thus to make increase the pH.) On the contrary, one bradypnée (slow and surface breathing) involves an accumulation of CO₂ and thus an acidification of blood.
the Rein S have two essential 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 (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.

During the metabolic alcalose, one a:

a generally high pH (superior with 7,42), but sometimes normal by respiratory compensation (hypoventilation)
of always high bicarbonates, higher than 26 mmol/L
a pCO₂ generally higher than 42 MmHg by compensation hypoventilation of the alcalose.

Etiologies

The alcalose occurs consecutively with several anomalies, often associated between them:

an increased contribution of bases, generally in the form of Bicarbonate of sodium or Bicarbonate of calcium,
an Acid S, in general by the kidney,
loss of Chlorine, digestive or renal loss of ,
a extracellular Dehydration, which involves a concentration of bicarbonates,
an increased reabsorption of bases by the Rein.

The role of chlorine (and its deficit in particular) is capital in the genesis of the metabolic alcaloses: indeed, the renal excretion of the bases possible that is not coupled with chlorine. The correction of a frequent chlorinated deficit is essential to return to the kidneys their capacity to remove blood from its excess of bases.

Excessive contribution of bases

Maybe by contribution of bicarbonate of sodium (for example at the insufficient renal one), or of bicarbonate of calcium (Syndrome of the “milk drinkers”.

Chlorine losses

digestive Losses (the saddles is very rich in chlorine. A Hypokaliémie is often associated): Vomiting S, digestive aspiration, digestive Tumor villous, etc
renal Losses.

Other causes

Hyperaldostéronismes
Disease of Cushing
Certain rare hereditary tubulopathies

Diagnosis

The clinical diagnosis is aspecific: it associates a muscular tetany, paraesthesias (abnormal feelings), to the maximum of the convulsions. Breathing is in general slow (bradypnée) by compensation. The diagnostic certainty is brought by gases of blood and the blood ionogramme (see higher). Other metabolic anomalies soivent being sought, because they are frequently associated: Hypokaliémie, hypocalcemy.

Treatment

Treatment etiologic

It is always essential, and often sufficient with the corrections of the metabolic anomalies:

Stop of an excessive bicarbonate catch,
Stop or reduction in a treatment by diuretic
Fight against the vomiting

etc

Symptomatic treatment

It rests not on an acidification of blood (except exceptional cases), but on the correction of the anomalies associated with the metabolic alcalose, and in particular the chlorinated deficit. This treatment is useful only for the deep alcaloses and/or source of a significant clinical repercussion.

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