Pediatric Hypernatremia

Hypernatremia is defined as a serum sodium concentration of more than 145 mEq/L. It is characterized by a deficit of total body water (TBW) relative to total body sodium levels due to either loss of free water; infrequently, the administration of hypertonic sodium solutions[1] ; or, even more uncommonly, administration of plasmalike isotonic fluids.[2]

In healthy subjects, the body's two main defense mechanisms against hypernatremia are thirst and the stimulation of vasopressin release.

Hypernatremia represents a deficit of water in relation to the body's sodium stores, which can result from a net water loss or a hypertonic sodium gain. Net water loss accounts for most cases of hypernatremia. Hypertonic sodium gain usually results from clinical interventions or accidental sodium loading. As a result of increased extracellular sodium concentration, plasma tonicity increases. This increase in tonicity induces the movement of water across cell membranes, causing cellular dehydration.

The following three mechanisms may lead to hypernatremia, alone or in concert:

• Pure water depletion (eg, diabetes insipidus)

• Water depletion exceeding sodium depletion (eg, diarrhea)

• Sodium excess (eg, salt poisoning)

Sustained hypernatremia can occur only when thirst or access to water is impaired. Therefore, the groups at highest risk are infants and intubated patients.

Because of certain physiologic characteristics, infants are predisposed to dehydration. They have a large surface area in relation to their height or weight compared with adults and have relatively large evaporative water losses. In infants, hypernatremia usually results from diarrhea and sometimes from improperly prepared infant formula or inadequate mother-infant interaction during breastfeeding. A retrospective study that evaluated data from 18 neonates with hypernatremic dehydration found that this condition most commonly occurs due to inadequate milk intake in breast or mixed fed babies, but only rarely as a result of feeding difficulties in infants with an acute infection.[3] In addition, not only was percentage weight loss at presentation strongly association with neonatal hypernatremic dehydration, but it was also the key factor for acute kidney injury in these infants.[3]

Hypernatremia causes decreased cellular volume as a result of water efflux from the cells to maintain equal osmolality inside and outside the cell. Brain cells are especially vulnerable to complications resulting from cell contraction. Severe hypernatremic dehydration induces brain shrinkage, which can tear cerebral blood vessels, leading to cerebral hemorrhage, seizures, paralysis, and encephalopathy.

In patients with prolonged hypernatremia, rapid rehydration with hypotonic fluids may cause cerebral edema, which can lead to coma, convulsions, and death.

A systemic review of the literature indicates that risk factors for breastfeeding-associated hypernatremia include the following[4] :

• Cesarean delivery

• Primiparity

• Breastfeeding difficulties

• Delayed breastfeeding

• Lack of previous breastfeeding experience

• Excessive maternal body weight

• Low maternal education level

Causes of hypovolemic hypernatremia include the following:

• Diarrhea

• Excessive perspiration

• Renal dysplasia

• Obstructive uropathy

• Osmotic diuresis

Causes of euvolemic hypernatremia include the following:

• Central diabetes insipidus causes

• Idiopathic causes

• Head trauma

• Suprasellar or infrasellar tumors (eg, craniopharyngioma, pinealoma)

• Granulomatous disease (sarcoidosis, tuberculosis, Wegener granulomatosis)

• Histiocytosis

• Sickle cell disease

• Cerebral hemorrhage

• Infection (meningitis, encephalitis)

• Associated cleft lip and palate

• Nephrogenic diabetes insipidus causes

• Congenital (familial) conditions

• Renal disease (obstructive uropathy, renal dysplasia, medullary cystic disease, reflux nephropathy, polycystic disease)

• Systemic disease with renal involvement (sickle cell disease, sarcoidosis, amyloidosis)

• Drugs (amphotericin, phenytoin, lithium, aminoglycosides, methoxyflurane)

Causes of hypervolemic hypernatremia include the following:

• Improperly mixed formula

• NaHCO3 administration

• NaCl administration

• Primary hyperaldosteronism

United States data

Hypernatremia is primarily a hospital-acquired condition occurring in children of all ages who have restricted access to fluids, mostly due to significant underlying medical problems such as a chronic disease, neurologic impairment, a critical illness, or prematurity. The incidence is estimated to be greater than 1% in hospitalized patients. Hospital-acquired hypernatremia accounts for 60% of hypernatremia cases in children. Gastroenteritis contributes to the hypernatremia in only 20% of cases. The group most affected is intubated, critically ill patients. Most cases result from a failure to freely administer water to patients. The incidence of breastfeeding-related hypernatremia is 1-2%.

International data

In developing nations, the reported incidence is 1.5-20%.

Race-, sex-, and age-related demographics

No racial or sexual predilection for hypernatremia in children is known.

In the pediatric population, hypernatremia usually affects newborns and toddlers who depend on caretakers for water, as well patients of any age who have significant underlying medical problems such as a chronic disease, neurologic impairment, a critical illness, or prematurity.

Patients usually recover from hypernatremia. Patients with recurrent hypernatremic dehydration develop neurologic sequelae, especially infants with diabetes insipidus.

Morbidity/mortality

In children with acute hypernatremia, mortality rates are as high as 20%. Extremely low birth weight infants with sodium level fluctuations during the first week of life are particularly at risk for death.[5] Neurologic complications related to hypernatremia occur in 15% of patients. The neurologic sequelae consist of intellectual deficits, seizure disorders, and spastic plegias. In cases of chronic hypernatremia in children, the mortality rate is 10%.

The neurolodevelopmental effects of hypernatremia in the first week of life of preterm infants born at less than 32 weeks' gestation has a long-term impact, including lower fine motor scores at 18 months of corrected age.[6]

Complications

Although seizures can occur because of hypernatremia per se, this is rare. They usually occur during the treatment of hypernatremia because of a rapid decline in serum sodium levels. Therefore, slowly correcting hypernatremia is important.

Other complications include the following:

• Mental retardation

• Intracranial hemorrhage

• Intracerebral calcification

• Cerebral infarction

• Cerebral edema, especially during treatment

• Hypocalcemia

• Hyperglycemia

Parents and caregivers should avoid making oral rehydration solutions at home or adding salt to any commercial infant formula.

Parents, especially breastfeeding mothers, should watch for neonatal dehydration and perinatal care.

The breastfed infant should be routinely monitored during the first weeks of life.[7]

In patients with diabetes insipidus, the following is indicated:

• Monitor weight and urine output because clinically significant changes in sodium values are associated with changes in weight.

• Restrict sodium and protein intake.

• The patient should drink liberal amounts of water.

• The patient and parents should ensure thirst develops before taking or giving medications.

Patients in certain situations or with certain conditions are at risk for hypernatremia, as follows:

• Hospitalized patients who receive exclusive intravenous fluids

• Patients with coma

• Newborns

• Toddlers

• Patients with diabetes insipidus

• Patients receiving alkali therapy

• Patients with diarrhea

• Patients with fever

• Patients with renal disorders (eg, dysplasia, medullary cystic disease, polycystic kidney disease, tubulointerstitial disease)

• Patients with obstructive uropathy

• Patients with electrolyte disturbances (eg, hypokalemia, hypercalcemia)

• Patients with heat stroke or excessive hypotonic fluid loss

Signs and symptoms of hypernatremia include the following:

• Irritability

• High-pitched cry or wail

• Periods of lethargy interspersed with periods of irritability

• Altered sensorium

• Seizures

• Increased muscle tone

• Fever

• Rhabdomyolysis[8, 9]

• Oligoanuria

• Excessive diuresis

Skin turgor is a physical finding in patients with hypernatremia. Extracellular and plasma volumes tend to be maintained in hypernatremic dehydration until dehydration is severe (ie, when the patient loses >10% of body weight).

When dehydration is severe, skin turgor is reduced, and the skin develops a characteristic doughy appearance.

Studies indicated in patients with suspected hypernatremia are listed below.

Serum tests

Obtain levels of sodium, osmolality, BUN, and creatinine.

Other laboratory measurements include aldosterone, cortisol, antidiuretic hormone (ADH), and corticotropin (ACTH) levels

Urine sodium concentration and osmolality

In cases of hypovolemic hypernatremia, extrarenal losses show urine sodium levels of less than 20 mEq/L, and in cases of renal losses, urine sodium values are more than 20 mEq/L.

In euvolemic hypernatremia, urine sodium data vary.

In hypervolemic hypernatremia, the urine sodium level is more than 20 mEq/L.

Imaging studies of the head should be considered in alert patients with severe hypernatremia to rule out a hypothalamic lesion affecting the thirst center.

CT scans may help in diagnosing intracranial tumors, granulomatous diseases (eg, sarcoid, tuberculosis, histiocytosis), and other intracranial pathologies.

MRI further delineates the pathology.

Medical care involves the correction of hypernatremia and treating the underlying disease.

However, avoid rapid correction of sodium levels in patients with chronic hypernatremia, because a rapid decline in the serum sodium concentration can cause cerebral edema.[10]

The recommended rate of sodium correction is 0.5 mEq/h or as much as 10-12 mEq/L in 24 hours. Dehydration should be corrected over 48-72 hours. Guidelines for hydration management have been established.[11] If the serum sodium concentration is more than 200 mEq/L, peritoneal dialysis should be performed using a high-glucose, low-sodium dialysate.

Body water deficit

Body water deficit may be calculated. The equations used are based on a goal of plasma sodium concentration of 145 mEq/L. In children, total body water (TBW) is 60% of their lean body weight. Therefore, TBW = 0.6 X weight. Babies are an exception to these equations and may have a TBW as much as 80% of their body weight.

One of the following equations may be used to calculate body water deficit:

• Water deficit (in L) = [(current Na level in mEq/L ÷ 145 mEq/L) - 1] X 0.6 × weight (in kg)

• Water deficit (in L) = [(current Na level in mEq/L - 145 mEq/L)/145 mEq/L)] × 0.6 X weight (in kg)

• Water deficit (in L) = [1- (145 mEq/L ÷ current Na level in mEq/L)] × 0.6 × weight (in kg)

An example calculation is: A child weighs 10 kg and has a plasma sodium concentration of 160 mEq/L. By using the first equation, water deficit (in L) = [(160 mEq/L ÷ 145 mEq/L) - 1] X 0.6 × 10 = 0.62 L.

Replacement fluid

The volume of replacement fluid needed to correct the water deficit is determined by using the concentration of sodium in the replacement fluid. The replacement volume can be determined as follows:

• Replacement volume (in L) = TBW deficit × 1 ÷ [1 - (Na concentration in replacement fluid in mEq/L ÷ 154 mEq/L)]

An example calculation is: If the patient from the example calculation above has a TBW of 0.62, and if the replacement fluid contains 0.2% NaCl (Na concentration of 34 mEq/L), the replacement volume (in L) = 0.62 L × 1 ÷ [1 - (34 mEq/L ÷ 154 mEq/L)] = 0.79 L. This volume has to be replaced slowly over 48-72 hours.

Intravenous fluid

The election of intravenous fluid is based on the following:

• If the patient is hypotensive, normal saline (lactated Ringer solution, or 5% albumin solution) should be used regardless of a high serum sodium concentration.

• In hypernatremic dehydration, 0.45% or 0.2% NaCl should be used as a replacement fluid to prevent excessive delivery of free water and a too-rapid decrease in the serum sodium concentration.

• In cases of hypernatremia caused by sodium overload, sodium-free intravenous fluid (eg, 5% dextrose in water) may be used, and a loop diuretic may be added.

• The serum sodium concentration should be monitored frequently to avoid too-rapid correction of hypernatremia.

• In cases of associated hyperglycemia, 2.5% dextrose solution may be given. Insulin treatment is not recommended because the acute decrease in glucose, which lowers plasma osmolality, may precipitate cerebral edema.

• Once the child is urinating, add 40 mEq/L KCl to fluids to aid water absorption into cells.

• Calcium may be added if the patient has an associated low serum calcium level.

Serum sodium levels

Serum sodium levels should be monitored every 4 hours.

Further inpatient care

Inpatient management also includes the following:

• Record daily body weights in patients with hypernatremia.

• Frequently monitor electrolyte concentrations.

• Restrict sodium and protein intake.

• Treat the underlying disease.

Transfer

Patients with symptomatic hypernatremia should be transferred to a pediatric intensive care unit for appropriate treatment and close monitoring.

Patients should be transferred to a facility that has dialysis in case of renal failure or in case the serum sodium concentration is more than 180 mEq/L.

Diet

In diabetes insipidus, a sodium-restricted and protein-restricted diet should be prescribed

Consultation is also recommended for patients with renal dysplasia, medullary cystic disease, reflux nephropathy, or polycystic disease. Consider obtaining consultations with the following specialists:

• Critical care specialist: Patients with symptomatic hypernatremia may need to be transferred to a pediatric ICU for appropriate treatment and monitoring.

• Endocrinologist: Consult an endocrinologist for patients with primary hyperaldosteronism.

• Nephrologist: Consult a nephrologist in cases of renal failure, obstructive uropathy, and serum sodium levels of more than 180 mEq/L for possible peritoneal dialysis.

The medications described below are used in patients with diabetes insipidus who have hypernatremia.

Class Summary

Desmopressin is a synthetic ADH with actions mimicking vasopressin. These agents are used to treat diabetes insipidus, which deprives the kidney of its capacity to produce concentrated urine. This effect results in large volumes of dilute urine (polyuria) and excessive thirst (polydipsia). Serum sodium concentrations may be elevated, but hypernatremia is most likely to be severe when fluid is restricted.

Desmopressin acetate (DDAVP)

Structural analog of vasopressin (ADH), the endogenous posterior pituitary hormone that maintains serum osmolality in a physiologically acceptable range. Works in neurohypophysial (eg, central) diabetes insipidus. Exerts similar antidiuretic effects. Vasopressin increases resorption of water at level of renal collecting duct, reducing urinary flow and increasing urine osmolality.

Vasopressin (Pitressin)

Exogenous, parenteral form of ADH. Antidiuretic and increases resorption of water at renal collecting ducts.

Class Summary

These drugs promote the excretion of water and electrolytes by the kidneys. They are used in patients with nephrogenic diabetes insipidus.

Hydrochlorothiazide (Esidrix, HydroDIURIL)

Works by increasing excretion of sodium, chloride, and water by inhibiting sodium ion transport across renal tubular epithelium. Resulting sodium depletion reduces glomerular filtration rate, enhancing reabsorption of fluid in proximal portion of nephron, decreasing delivery of sodium to ascending limb of loop of Henle and consequently reducing capacity to dilute urine.