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Endocrinology

Hyponatremia and hypernatremia

Table of contents
Hyponatremia and hypernatremia
Hyponatremia reasons
Hypernatremia reasons
Anamnesis of a hyponatremia
Anamnesis of a hypernatremia
Physical inspection
Diagnostic testings
Assessment

Close concepts: gipoosmolyarny state, water intoxication, giperosmolyarny state, dehydration

The hyponatremia means reduction of plasma or serumal concentration of sodium lower than 135 mmol/l, and a hypernatremia — increase in plasma concentration of sodium out of limits of 145 mmol/l. These terms mean a ratio in plasma of amount of sodium and water and do not belong to increase or reduction of the general content of sodium in an organism. The hyponatremia and a hypernatremia represent primary disturbances of a water balance resulting from frustration in system of regulation of osmolarity which activity is directed to maintenance (generally due to change of excretion and digestion of water) to osmolarity of a blood plasma in narrow limits, components 280 — 295 mosm/kg waters.

Osmolarity of plasma (Rosm) represents the total number of the solid substances which are in plasma water expressed in mosm/kg waters. As sodium is the main cation of a blood plasma, its concentration changes parallel to osmolarity of plasma that is expressed by the following equation:

Rosm = 2 (Na + To mmol/l) + glucose (% mg)/18 + an urea nitrogen (mg)/2.8

Effective osmolarity or tonicity is created due to concentration of those substances which raise an osmotic gradient on cellular membranes and cause water movement. Urea which freely diffuses through a cellular membrane has identical concentration in extracellular liquid and in a cell and does not exert impact on tonicity.

At normal concentration of glucose the troichnost of plasma can be counted approximately as 2 (Na + K) mmol/l.

The acute hyponatremia and acute hyponatremia represent states at which changes of plasma concentration of sodium happen quickly (less than for 48 h). As it will be shown below, the speed of change of plasma concentration of sodium has both diagnostic, and predictive value.

At a pseudo-hyponatremia false low concentration of sodium in a blood plasma are defined. Normal plasma contains more than 90% of water and about 10% of solid substances. Increase in contents in a blood plasma of solid substances, for example at a lipidemia or a hyperproteinemia, causes relative reduction of content of water in it. In spite of the fact that the content of sodium in plasma water can be normal, the value of concentration of sodium expressed in plasma mmol/l is lowered.
The hyponatremia with hypertonicity belongs to clinical states at which as a result of increase of concentration of osmotically active agents (except for sodium), for example glucose, there is a movement of water from a cell in a blood plasma and dilution contained in drink sodium.



 
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