0521779407-09 CUNY1086/Karliner 0 521 77940 7 June 13, 2007 7:54
792 Hyponatremia➣Due to flame photometry methods used in many laboratories
➣Direct (undiluted) ion-specific electrodes are accurate for Na
measurements.
■Translocational Hyponatremia
➣Associated with high serum osmolality
➣The osmotically active substance draws the water out of the cells
and lowers the serum sodium.
➣Common causes are uncontrolled diabetes, glycine intoxication
(endometrial and prostatic surgeries) and mannitol therapy.
➣With hyperglycemia, serum sodium falls approximately by 1.6
mEq/L for each 100-mg/dL rise in blood glucose.
■Hypoosmolar Hyponatremia
➣Assessment of volume status and urinary Na provides a useful
classification.
➣Hypovolemic hyponatremia and Urine Na <10 mEq/L
Vomiting, diarrhea, third-space losses (pancreatitis)
➣Hypovolemic hyponatremia and Urine Na >20 mEq/L
Diuretic, mineralocorticoid deficiency, osmotic diuresis
➣Euvolemic hyponatremia (Urine Na >20 mEq/L usually)
Glucocorticoid deficiency, hypothyroidism, physical or emo-
tional stress, drugs (morphine, nicotine), syndrome of inap-
propriate antidiuretic hormone secretion (SIADH)
SIADH:
Associated with hypo-osmolality, a urine osmolality >100
mOsmol/kg, urine sodium concentration that is usually >40
mEq/L, normal acid-base and potassium balance, and fre-
quently a low plasma uric acid concentration
Diagnosis of exclusion
Some important causes include carcinomas, pulmonary disor-
ders, CNS disorders, AIDS and geriatric patients (idiopathic).
➣Hypervolemic hyponatremia and Urine Na >20 mEq/L
Acute and chronic renal failure
➣Hypervolemic hyponatremia and Urine Na <10 mEq/L
Nephrotic syndrome, cirrhosis, cardiac failuremanagement
n/a
specific therapy
■Depends on 2 factors: symptoms and duration
■Acute Symptomatic Hyponatremia
➣Goal: Increase serum Na until symptoms resolve