Sodium imbalance (pediatrics)

Sodium Dysbalance represents one of the most common ionic changes. Sodium is the main cation of ECT and is of key importance to the osmolality of this body compartment. In ICT the concentration of sodium is not the same everywhere, it varies between 3 - 35 mmol/l, but it is always lower than in ECT. The difference in Na concentrations between ICT and ECT (sodium concentration gradient) is the result of the active metabolic activity of cells, especially the so-called sodium pumps = Na-K-ATPase. Due to the action of this mechanism located in the cell membrane, sodium ions are constantly expelled from ICT to ECT, potassium ions move in the opposite direction. In situations of energy depletion, the activity of Na-K-ATPase is paralyzed and the movement of both mentioned ions changes to the opposite.

Dietary sodium intake is highly individual, 4 – 15 g NaCl (i.e. 70 – 250 mmol/24 hours). The largest part of the ingested sodium is excreted by the kidneys, however, significant extrarenal losses can occur through the skin during excessive sweating (especially in children with a high concentration of Na in sweat - patients with cystic fibrosis ). With good kidney function and no increase in the proportion of extrarenal losses, it is possible to calculate with a balanced sodium balance, i.e. p.o. intake corresponds to its excretion in urine. This aspect enables a practical assessment of sodium balance, when the amount of Na excreted in the urine can be converted to NaCl intake.

Example: if the amount of excreted Na was 148 mmol/24 h, it means that the child took in 148 : 17 = 8.7 g of NaCl.

Changes in sodium concentration are always accompanied by a redistribution of body water in individual compartments. ECT hyponatremia leads to a decrease in its osmolality with a subsequent movement of water into the ICT. This redistribution is accompanied by a rise in ECT osmolality. ECT hypernatremia induces exactly the opposite changes. Correct kidney function is determining for all the above data. Sodium ions freely penetrate the glomerular membrane and their concentration in the glomerular filtrate is identical to the S-Na value. In the proximal tubule of the kidney, 50-70% of sodium is resorbed, and <1% of the total filtered sodium eventually reaches the final urine. The value determining what part of the filtered sodium is excreted in the urine is referred to as the fractional excretion of FE Na. The determination of FE Na is used to evaluate renal tubular function and is also one of the auxiliary parameters to distinguish the initial cause of acute renal failure (difference between renal and prerenal ASL).

Related Articles

 * Hyponatremia (pediatrics)
 * Hypernatremia (pediatrics)
 * Indoor Environment (Paediatrics)
 * Serum osmolality
 * Sodium imbalance
 * Hyponatremia
 * Hypernatremia

Source

 * HAVRÁNEK, Jiří: Sodium Dysbalance. (edited)