Dehydration in children

Dehydration is a significant loss of water and usually electrolytes. Symptoms of dehydration in children include thirst, lethargy, dry mucous membranes, decreased urine output, and, as dehydration progresses, tachycardia, hypotension, and shock. Diagnosis is based on history and physical examination. Treatment of dehydration in children is with oral or intravenous fluid and electrolyte replacement.

Dehydration, usually due to diarrhea, remains a major cause of morbidity and mortality in infants and young children worldwide. Infants are particularly susceptible to dehydration and its adverse effects because they have higher fluid requirements (due to a higher metabolic rate), higher fluid losses (due to a higher surface area to volume ratio), and an inability to communicate thirst or seek fluids.

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What causes dehydration in children?

Dehydration occurs as a result of increased fluid loss, decreased fluid intake, or a combination of both.

The most common source of fluid loss is through the gastrointestinal tract due to vomiting, diarrhea, or a combination of the two (gastroenteritis). Other sources of fluid loss include the kidneys (diabetic ketoacidosis), skin (excessive sweating, burns), and fluid loss into the cavity (into the intestinal lumen due to intestinal obstruction). In all of these cases, the fluid that the body loses contains electrolytes in varying concentrations, so fluid loss is always accompanied by electrolyte loss.

Decreased fluid intake is common during any serious illness and is most serious with vomiting and hot weather. It can also be a sign of poor care for the baby.

Symptoms of Dehydration in Children

Symptoms of dehydration in children may vary depending on the degree of fluid deficit and depend on the concentration of sodium in the blood serum: the effect on the child's hemodynamics is increased by hyponatremia and decreased by hypernatremia. In general, dehydration without hemodynamic disturbances is considered mild (approximately 5% of body weight in infants and 3% in adolescents); tachycardia is observed with a moderate degree of dehydration (approximately 10% of body weight in infants and 6% in adolescents); hypotension with microcirculation disorders indicates severe dehydration (approximately 15% of body weight in infants and 9% in adolescents). A more accurate method for assessing the degree of dehydration is to determine the change in body weight; it is believed that in any case, a loss of more than 1% of body weight per day is associated with fluid deficit. At the same time, this method depends on knowing the child's exact weight before the disease. Parents' estimates, as a rule, do not correspond to reality; A 1 kg error in a 10 kg child leads to a 10% error in calculating the degree of dehydration - this is the difference between mild and severe.

Laboratory testing is usually needed in patients with moderate to severe illness, who frequently develop electrolyte disturbances (hypernatremia, hypokalemia, metabolic acidosis). Other laboratory changes include relative polycythemia due to hemoconcentration, increased blood urea nitrogen, and increased urine specific gravity.

Treatment of dehydration in children

The best approach to treatment is to divide the rehydration fluid into fluid for emergency correction, replacement of deficit, ongoing pathological losses, and physiological needs. The volume (amount of fluid), composition of solutions, and rate of replenishment may vary. Formulas and assessment tables provide only initial data, but therapy requires ongoing monitoring of the child: assessment of hemodynamics, appearance, urine output and specific gravity of urine, body weight, and sometimes blood electrolyte levels. Children with severe dehydration are given parenteral rehydration. Children who are unable or refuse to drink, as well as children with repeated vomiting, are prescribed intravenous rehydration, fluid administration through a nasogastric tube, and sometimes oral rehydration is used - frequent fractional drinking.

Emergency correction of dehydration in newborns

Patients with signs of hypoperfusion should undergo emergency correction of fluid deficit with bolus administration of saline (0.9% sodium chloride solution). The goal is to restore adequate circulating volume to maintain blood pressure and microcirculation. The emergency correction phase should reduce the degree of dehydration from moderate or severe to a deficit of approximately 8% of body weight. If dehydration is moderate, 20 ml/kg (2% of body weight) of the solution is administered intravenously over 20-30 minutes, reducing the fluid deficit from 10% to 8%. In severe dehydration, 2-3 bolus administrations of 20 ml/kg (2% of body weight) of the solution will probably be required. The result of the emergency correction phase is restoration of peripheral circulation and blood pressure, normalization of the increased heart rate. Compensation of fluid deficit.

The total fluid deficit is determined clinically as described above. The sodium deficit is usually 80 mEq/L of fluid loss, and the potassium deficit is approximately 30 mEq/L of fluid loss. During the acute correction phase of severe or moderate dehydration, the fluid deficit should have decreased to 8% of body weight; this remaining deficit should be replaced at a rate of 10 mL/kg (1% of body weight)/hour over 8 hours. Because 0.45% saline contains 77 mEq of sodium per liter, it is usually the solution of choice. Potassium replacement (usually by adding 20 to 40 mEq of potassium per liter of solution) should not be attempted until adequate urine output has been established.

Dehydration with significant hypernatremia (serum sodium level greater than 160 mEq/L) or hyponatremia (serum sodium level less than 120 mEq/L) requires special attention to prevent complications.

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Continued losses

The volume of ongoing losses should be measured directly (by nasogastric tube, catheter, stool volume measurement) or estimated (e.g., 10 ml/kg stool for diarrhea). Replacement should be equal to the milliliter of loss and should be given over a time period consistent with the rate of ongoing losses. Ongoing electrolyte losses can be estimated based on the source or cause. Renal electrolyte losses vary with intake and the disease process but can be measured if the deficit cannot be corrected by replacement therapy.

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Physiological need

Physiological fluid and electrolyte requirements must also be taken into account. Physiological requirements depend on the basal metabolic rate and body temperature. Physiological losses (water loss through the skin and through respiration in a ratio of 2:1) account for approximately 1/2 of the physiological requirement.

An exact calculation is rarely necessary, but usually the volume should be sufficient so that the kidney does not need to significantly concentrate or dilute the urine. The most common method uses the patient's weight to determine energy expenditure in kcal/day, which approximates physiological fluid requirements in ml/day.

A simpler calculation method (Holiday-Segar formula) uses 3 weight classes. It is also possible to use the calculation for the child's body surface area determined by nomograms, the physiological fluid requirement will be 1500-2000 ml/(m2 x day). More complex calculations are rarely used. The calculated volume can be administered as a separate infusion simultaneously with those already described, so that the infusion rate of fluid replacement and ongoing pathological losses can be established and changed independently of the maintenance infusion rate.

The calculated volume of physiological requirement may change with fever (increasing by 12% for each degree above 37.8 °C), hypothermia, physical activity (increases with hyperthyroidism and epileptic status, decreases with coma).

The composition of the solutions differs from those used to compensate for fluid deficit and ongoing pathological losses. The patient requires 3 mEq/100 kcal/day of sodium (meq/100 ml/day) and 2 mEq/100 kcal/day of potassium (meq/100 ml/day). This requirement is met by a 0.2-0.3% solution of sodium chloride with 20 mEq/l of potassium in 5% glucose solution (5% G/V). Other electrolytes (magnesium, calcium) are not routinely prescribed. It is incorrect to compensate for fluid deficit and ongoing pathological losses by only increasing the volume and rate of infusion of the maintenance solution.