Other Abnormalities of Arginine Vasopressin Metabolism and Action

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Chapter 553 Other Abnormalities of Arginine Vasopressin Metabolism and Action

Hyponatremia (serum sodium <130 mEq/L) in children is usually associated with severe systemic disorders and is most often due to intravascular volume depletion, excessive salt loss, or hypotonic fluid overload, especially in infants (Chapter 52). The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is an uncommon cause of hyponatremia in children.

The initial approach to the patient with hyponatremia begins with determination of the volume status. A careful review of the patient’s history, physical examination, including changes in weight, and vital signs helps determine whether the patient is hypovolemic or hypervolemic. Supportive evidence includes laboratory data such as serum electrolytes, blood urea nitrogen, creatinine, uric acid, urine sodium, specific gravity, and osmolality (Chapter 52.3; Tables 553-1 and 553-2).

Table 553-1 DIFFERENTIAL DIAGNOSIS OF HYPONATREMIA

DISORDER INTRAVASCULAR VOLUME STATUS URINE SODIUM
Systemic dehydration Low Low
Decreased effective plasma volume Low Low
Primary salt loss (nonrenal) Low Low
Primary salt loss (renal) Low High
SIADH High High
Cerebral salt wasting Low Very high
Decreased free water clearance Normal or high Normal or high
Primary polydipsia Normal or high Normal
Runner’s hyponatremia Low Low
NSIAD High High
Pseudohyponatremia Normal Normal
Factitious hyponatremia Normal Normal

NSIAD, nephrogenic syndrome of inappropriate antidiuresis; SIADH, syndrome of inappropriate antidiuretic hormone secretion.

Causes of Hyponatremia

Systemic Dehydration

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