0521779407-09 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 21:13
752 Hypernatremia■Hypernatremia
➣Seen more with acute hypernatremia
➣Nonspecific CNS symptoms due to cellular dehydration
➣Subcortical and subarachnoid bleeding have been described due
to tearing of cerebral blood vessels.
tests
■Basic metabolic profile
■Other tests in differential diagnosis of hypernatremia
➣Serum osmolality
➣Urine sodium
➣Urine osmolality
➣ADH measurement is expensive and unnecessary.
differential diagnosis
■Central diabetes insipidus vs. nephrogenic diabetes insipidus
■Do a water deprivation test followed by a DDAVP challenge. In both
setting the urine remains hypotonic (<300 mOsm/Kg) or isotonic
(∼300 mOsm/Kg) with water deprivation, but in central diabetes
insipidus only, the urine osmolality increases with DDAVP.Approach to Hypernatremia
■Based on the volume status and Urine Na, it can be divided into
following categories:
■Hypovolemic hypernatremia and Urine Na <10 mEq/L
➣Urine is hypertonic (>300 mOsm/Kg)
➣Extrarenal hypoosmolar losses – i.e., sweating, febrile states,
burns, diarrhea, fistulas
■Hypovolemic hypernatremia and Urine Na >20 mEq/L
➣Urine is hypotonic or isotonic
➣Renal hypo-osmolar losses: diuretic use, osmotic diuresis, renal
disease, post obstruction
■Hypervolemic hypernatremia (Urine Na is usually >20 mEq/L)
➣Urine is hypertonic or isotonic
➣Hypertonic Na (usually Na bicarbonate) administration, primary
hyperaldosteronism, Cushing’s syndrome
■Euvolemic hypernatremia (Urine Na and osmolality variable)
➣Renal losses of water due to the deficiency or resistance of ADH
secretion
➣Central diabetes insipidus – defect in ADH production
Idiopathic or secondary to malignancies, infections or granu-
lomatous diseases of the pituitary gland