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Dehydration or volume depletion is classified as mild, moderate or severe based on how much body fluid is lost. When severe, dehydration is a life-threatening emergency. Volume depletion denotes lessening of the total intravascular plasma, whereas dehydration denotes loss of plasma-free water disproportionate to the loss of sodium. Potassium and other electrolytes including buffers líke phosphates need to be considered. Children, especially those younger than 4 years old, are more susceptible to volume depletion as a result of vomiting, diarrhea or increases in insensible water losses.
Dehydration can be caused by losing too much fluid, not drinking enough water or fluids, or both. Vomiting and diarrhea are common causes.
In addition to the symptoms of actual dehydration, you may also have:
Intravenous fluids and hospitalization may be necessary for moderate to severe dehydration. The doctor will try to identify and then treat the cause of the dehydration.
Most cases of stomach viruses (also called viral gastroenteritis) tend to resolve on their own after a few days.
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.
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. Significant fluid 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:
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 person may appear more ill clinically than fluid losses indicate. 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. An example 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 must be 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 shifts between intracellular and extracellular fluid compartments occur more slowly than free water shifts. Serum potassium level may not reflect intracellular potassium levels. Although a potassium deficit is present in all patients with volume depletion, it is not usually clinically significant. However, failure to correct for a potassium deficit during volume repletion may result in clinically significant hypokalemia. Potassium should not be added to replacement fluids until adequate urine output is obtained.
Clinicians may observe derangements of acid-base balance with volume depletion. Some degree of metabolic acidosis is common, especially in infants. Mechanisms include bicarbonate loss in stool and ketone production. Hypovolemia causes decreased tissue perfusion and increased lactic acid production. Decreased renal perfusion causes decreased glomerular filtration rate, which, in turn, leads to decreased hydrogen (H+) ion excretion. These factors combine to produce a metabolic acidosis.
In most patients, acidosis is mild and easily corrected with volume restoration (as increased renal perfusion permits excretion of excess H+ ions in the urine). Administration of glucose-containing fluids further decreases ketone production.
Morbidity varies with the degree of volume depletion and the underlying cause.
Infants and younger children are more susceptible to volume depletion than older children.
The emergency physician should be diligent in obtaining the following information:
Of these, the most accurate in identifying the level of dehydration are capillary refill, skin turgor, and breathing. The least accurate are mental status, heart rate and fontanelle appearance.
In most cases, volume depletion in children is from fluid losses from vomiting or diarrhea.
Diarrhea may be caused by any of the following systems or processes:
Volume depletion not caused by vomiting or diarrhea may be divided into renal or extrarenal causes.
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