Medical Care
The American Academy of Pediatrics (AAP) strongly recommends that patients aged 28 days to 18 years who require maintenance intravenous fluids (IVFs) receive isotonic solutions with appropriate potassium chloride (KCl) and dextrose, due to their significantly lowered risk of developing hyponatremia with these solutions. [15]
Principles of treatment in hyponatremia
The most common and devastating effects of hyponatremia are of central nervous system (CNS) origin. Therefore, identifying the risk factors that lead to hyponatremia and instituting prompt treatment while avoiding complications is crucial.
Although cerebral adaptation to low serum Na occurs slowly, it protects the brain from deleterious effects of hypo-osmolality. However, this protective mechanism leaves the brain susceptible to osmotic demyelination syndrome (ODS) during treatment, especially in persons with chronic hyponatremia, if the correction is rapid.
Equations used in managing hyponatremia
To estimate the effect of 1 L of any infusate on serum Na concentration
-
Change in Na concentration = (infusate Na level - serum Na level)/(total body water + 1)
To estimate the effect of 1 L of any infusate containing Na and potassium (K) on serum Na concentration
-
Change in serum Na level = [(infusate Na level + infusate K level) - serum Na level]/(total body water + 1)
Na concentrations of various fluids used in pediatric practice
Note the following:
-
5% NaCl in water: 855 mEq/L
-
3% NaCl in water: 513 mEq/L
-
0.9% NaCl in water: 154 mEq/L
-
Ringer lactate solution: 130 mEq/L
-
0.45% NaCl in water: 77 mEq/L
-
0.2% NaCl in water: 34 mEq/L
-
5% dextrose in water: 0 mEq/L
Management of hypovolemic hyponatremia
The immediate goal is to correct volume depletion with normal saline. As soon as the patient is hemodynamically stable, hyponatremia should be corrected as per the treatment principles described below. In patients with seizure, 3% NaCl should be given while volume depletion is being corrected.
No consensus has been reached about the optimal treatment of symptomatic hyponatremia. However, guidelines for hydration management have been established. [16] Physiologic considerations indicate that a relatively small increase in the serum Na concentration, on the order of 5%, should substantially reduce cerebral edema. Available evidence indicates that even a 9 mEq/L increase in serum Na concentration over 24 hours can result in demyelinating lesions. Given the risk of demyelinating lesions, the recommended rate of correction should not exceed 8 mEq/L/d. Even hyponatremia-induced seizures can be stopped with changes in serum Na concentration of only 3-7 mEq/L.
Treatment of normovolemic hyponatremia due to syndrome of inappropriate antidiuretic hormone secretion (SIADH) can include fluid restriction, along with the administration of normal saline; the use of 3% NaCl, and intravenous (IV) administration of furosemide may also be needed. Furosemide is given to offset the volume expansion created by the 3% Na infusion. As previously discussed, when confronted with neurologic symptoms the plan is to raise the serum Na concentration until symptoms resolve, this can be done by giving doses of 1-2 mL/Kg of 3% saline, symptoms typically resolve with a rise in sodium of 3-7 mEq/L; subsequently, closely monitor electrolyte levels so that the correction does not exceed 8 mEq/L/d. This appears to leave little room for elevation of serum sodium after immediately addressing symptoms; however, it appears that maintaining control of the absolute rise over 24 hours remains beneficial, even after the immediate emergent increase in serum sodium.
Management of hypervolemic hyponatremia
In patients with hypervolemic hyponatremia, restrict fluids, administer 3% NaCl to stop the symptoms, and treat the underlying cause.
Management of asymptomatic hyponatremia
In asymptomatic individuals with hypovolemic hyponatremia, one should not rush to correct hyponatremia. The main principle is to avoid hypotonic fluids and to slowly correct Na levels, especially when hyponatremia has been present for 48 hours or longer. When the duration of hyponatremia is unknown, as is encountered in outpatient settings, assume hyponatremia is chronic and treat accordingly. Closely monitor electrolyte values, and the rate of correction should not exceed 8 mEq/L/d.
In patients with normovolemic hyponatremia, restriction of fluids to two-thirds (or less) of the volume needed for maintenance is the mainstay of treatment. Diuretics can be administered with fluid restriction to remove excessive free water. Once again, the change in Na levels should not exceed 8 mEq/L/d.
In recalcitrant euvolemic hyponatremia, one can use demeclocycline to induce therapeutic nephrogenic diabetes insipidus, which might help eliminate excessive water. However, one must remember that total correction should not exceed the established goal.
Diet
Patients with salt-wasting disorders (eg, salt-losing nephropathies) need Na supplementation throughout the period of continued loss of excessive Na.
Patients with SIADH and renal failure require fluid restriction.
Consultations
Transfer patients with symptomatic hyponatremia to a pediatric intensive care unit (PICU) for appropriate treatment and close monitoring.
Consult an endocrinologist when patients have hypothyroidism or adrenal insufficiency.
Consult a nephrologist when patients have salt-losing nephropathy, renal failure, or recalcitrant hyponatremia.
Appropriate neurosurgical care is required when central nervous system (CNS) conditions are the cause of syndrome of inappropriate antidiuretic hormone secretion (SIADH).
Prevention
Carefully monitor patients receiving drugs that can cause hyponatremia.
Give careful consideration to the type of intravenous (IV) hydrating solution used in pediatric patients. The findings of one study conclude that the use of hypotonic maintenance fluids increases the incidence of hyponatremia because they decrease blood sodium levels in normonatremic patients. Isotonic maintenance fluids did not increase the incidence of dysnatremia and showed a reduced incidence of hyponatremia in the patients studied. The findings suggest that the administration of isotonic fluids should be considered the standard of care in critically ill children. [17]
Prudently monitor serum electrolytes in postoperative patients, patients on IV fluids, and in those with brain tumors, intracranial infections, pulmonary infections, or head trauma.
-
Pediatric Hyponatremia. Drugs that impair water excretion.
