Approach to pt with polyuria , polydipsia and hyponatremia

The cause of pathologic polyuria or polydipsia (exceeding 2 L/m2/24 hr) may be difficult to establish in children. Infants may present with irritability, failure to thrive, and intermittent fever.

History:

Patients with suspected DI should have a careful history taken, which should quantify the child's daily fluid intake and output and establish the voiding pattern, nocturia, and primary or secondary enuresis

Examination:

A complete physical examination should establish the patient's hydration status, and the physician should search for evidence of visual and central nervous system dysfunction as well as other pituitary hormone deficiencies

Investigations:

If pathologic polyuria or polydipsia is present, the following should be obtained:

serum for osmolality,

serum sodium, potassium, blood urea nitrogen, creatinine, glucose, and calcium;

urine for osmolality, specific gravity, and glucose determination.

The diagnosis of DI is established if the serum osmolality is greater than 300 mOsm/kg and the urine osmolality is less than 300 mOsm/kg.

If the patient's serum osmolality is less than 300 mOsm/kg (but greater than 270 mOsm/kg) and pathologic polyuria and polydipsia are present, a water deprivation test is indicated to establish the diagnosis of DI and to differentiate central from nephrogenic causes.

In the inpatient post-neurosurgical setting, central DI is likely if hyperosmolality (serum osmolality >300 mOsm/kg) is associated with urine osmolality less than serum osmolality. It is important to distinguish between polyuria resulting from postsurgical central DI and polyuria resulting from the normal diuresis of fluids received intraoperatively. Both cases may be associated with a large volume (>200 mL/m2/h) of dilute urine, although in patients with DI, the serum osmolality is high in comparison with patients undergoing postoperative diuresis