Problem. A 7-day-old infant with an intraventricular bleed has a serum sodium level of 127 mEq/L, below the normal accepted value of 135 mEq/L.
Is there any seizure activity? Seizure activity is often seen in patients with extremely low serum sodium levels (usually <120 mEq/L). This is a medical emergency, and urgent sodium correction is needed.
How much sodium and free water is the patient receiving? Is weight gain or loss occurring? Be certain that an adequate amount of sodium is being given and that free water intake is not excessive. The normal amount of sodium intake is 2–4 mEq/kg/day. Weight gain with low serum sodium levels is most likely a result of volume overload, especially in the first day or two of life when weight loss is expected.
What is the urine output? With syndrome of inappropriate secretion of anti-diuretic hormone (SIADH), urine output is decreased. If the urine output is increased (>4 mL/kg/h), perform a spot check of urine sodium to determine whether sodium losses are high.
Are renal salt-wasting medications being given? Diuretics such as furosemide may cause hyponatremia.
Differential diagnosis. When considering the differential, determine if the value is real. Certain conditions can cause pseudohyponatremia. Is the amount of sodium given adequate? Then you need to decide if the hyponatremia is caused by deficit of total body sodium or an excess of free water. Have medications caused the hyponatremia? Deciding the cause dictates the form of treatment. The most frequent cause of hyponatremia in the neonate is hypotonic hyponatremia caused by excessive fluid administration or retention of free water.
Exclude pseudohyponatremia. Laboratory tests reveal a decreased sodium, but serum osmolality is normal. Caused by hyperproteinemia, hyperglycemia, or hyperlipidemia.
Inadequate sodium intake. Maintenance is usually 2–4 mEq/kg/day.
Hyponatremia with hypervolemia. This occurs with excess of extracellular fluid. There is a positive water balance. The infants have signs of edema and weight gain. Causes include the following:
Congestive heart failure.
Sepsis with decreasing cardiac output.
Neuromuscular paralysis with fluid retention (with pancuronium).
Hyponatremia with hypovolemia. This occurs with a deficit of extracellular fluid and can be caused by either renal losses or extrarenal losses.
Renal losses (urinary Na >20mEq/L)
Congenital adrenal hyperplasia.
Osmotic diuresis. One case report presented this secondary to renovascular hypertension caused by a thrombotic occlusion.
Bartter and Fanconi syndrome.
Renal immaturity. Often very low birthweight infants show increased renal tubular sodium and water loss, causing hyponatremia. (See Chapter 16.)
Renal tubular acidosis.
Extrarenal losses (urinary Na <20mEq/L)
Gastrointestinal (GI) losses such as vomiting, diarrhea, nasogastric tubes.
Third spacing of fluids due to ascites, pleural effusion, ileus, necrotizing enterocolitis, sloughing of skin.
Radiant warmer skin loss.
Hyponatremia with normal extracellular fluid.
Excessive IV fluids, free water or using diluted (hypotonic) formulas is a common cause of the hyponatremia in a neonate. Maternal water intoxication is also a cause of hyponatremia in a newborn. Associated with low urine specific ...
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