Deshidratacion

Pediatric dehydration is frequently the result of gastroenteritis, characterized by vomiting and diarrhea. However, other causes of dehydration may include poor oral intake due to diseases such as stomatitis, insensible losses due to fever, or osmotic diuresis from uncontrolled diabetes mellitus.

The terms dehydration and volume depletion are commonly used interchangeably to denoteintravascular fluid depletion. However, it is useful for clinicians to understand that volume depletion is distinct from dehydration. Volume depletion denotes contraction of the total intravascular plasma pool, whereas dehydration denotes loss of plasma free water disproportionate to loss of sodium, the main intravascular solute. The distinction is important because volume depletion can exist with or withoutdehydration, and dehydration can exist with or without volume depletion.

In children with dehydration, the most common underlying problem actually is volume depletion, not dehydration. Intravascular sodium levels are within the reference range, indicating that excess free water is not being lost from plasma. Rather, the entire plasma pool is contracted with solutes (mostly sodium) and solvents(mostly water) lost in proportionate quantities. This is volume depletion without dehydration. The most common cause is excessive extrinsic loss of fluids in conditions such as vomiting and diarrhea.

Pediatric patients, especially those younger than 4 years, tend to be more susceptible to volume depletion as a result of vomiting, diarrhea, or increases in insensible water losses. Significantfluid losses may occur rapidly. The turnover of fluids and solute in infants and young children can be as much as 3 times that of adults. This is because of the following:
* Higher metabolic rates
* Increased body surface area to mass index
* Higher body water contents (Water comprises approximately 70% of body weight in infants, 65% in children, and 60% in adults.)
Sodiumconsiderations

Volume depletion can be concurrent with hyponatremia. This is characterized by plasma volume contraction with free water excess. An example is a child with diarrhea who has been given tap water to replete diarrheal losses. Free water is replenished, but sodium and other solutes are not.

In hyponatremic volume depletion, the patient may appear more ill clinically than fluid lossesindicate. The degree of volume depletion may be clinically overestimated. Serum sodium levels less than 120 mEq/L may result in seizures. If intravascular free water excess is not corrected during volume replenishment, the shift of free water to the intracellular fluid compartment may cause cerebral edema.

With true dehydration, plasma volume contracts with disproportionate further free water loss. Anexample is the child with diarrhea whose fluid losses have been replenished with hypertonic soup, boiled milk, baking soda, or improperly diluted infant formula. Volume has been restored, but free water has not.

In hypernatremic volume depletion, the patient may appear less ill clinically than fluid losses indicate. The degree of volume depletion may be underestimated. Usually, at least a 10%volume deficit exists with hypernatremic volume depletion.

As in hyponatremia, hypernatremic volume depletion may result in serious central nervous system (CNS) effects as a result of structural changes in central neurons. However, cerebral shrinkage occurs instead of cerebral edema. This may result in intracerebral hemorrhage, seizures, coma, and death. For this reason, volume restoration mustbe performed gradually over 24 hours or more. Gradual restoration prevents a rapid shift of fluid across the blood-brain barrier and into the intracellular fluid compartment.

Potassium considerations

Potassium shifts between intracellular and extracellular fluid compartments occur more slowly than free water shifts. Serum potassium level may not reflect intracellular potassium levels....