Hyponatremia

Hyponatremia management

1. Hyponatremia [Na] < 135 mEq /L

2. Extracellular-Fluid and Intracellular-Fluid Compartments under Normal Conditions and during States of Hyponatremia.

3. Effects of Hyponatremia on the Brain and Adaptive Responses.

4. Clinical Signs of Hyponatrema Nausea, vomiting, anorexia, muscle cramps, confusion, and lethargy, and culminate ultimately in seizures and coma. Seizures are quite likely at [Na + ] of 113 mEq /L or less.

5. Causes of Hyponatremia Hypertonic Hyponatremia Osmotic Pressure >295 Isotonic Hyponatremia Osmotic Pressure 275 to 295 Hypotonic Hyponatremia Osmotic Pressure <275

6. Hypertonic hyponatremia ( P osm >295) Hyperglycemia   Mannitol excess   Glycerol therapy

7. Isotonic (pseudo) hyponatremia ( P osm 275–295) Hyperlipidemia    Hyperproteinemia (e.g., multiple myeloma, Waldenström macroglobulinemia )

8. Hypotonic hyponatremia ( P osm <275) Hypovolemic      Renal        Diuretic use        Salt-wasting nephropathy (renal tubular acidosis, chronic renal failure, interstitial nephritis)        Osmotic diuresis (glucose, urea, mannitol , hyperproteinemia )        Mineralocorticoid ( aldosterone ) deficiency Extrarenal         Volume replacement with hypotonic fluids        GI loss (vomiting, diarrhea, fistula, tube suction)        Third-space loss (e.g., burns, hemorrhagic pancreatitis, peritonitis)   Hypervolemic       Urinary [Na + ] >20 mEq /L Renal failure (inability to excrete free water)     Urinary [Na + ] <20 mEq /L Congestive heart failure Nephrotic syndrome    Cirrhosis Euvolemic urine [Na + ] usually > 20 mEq /L SIADH Hypothyroidism (possible increased ADH or deceased glomerular filtration rate)     Pain, stress, nausea, psychosis (stimulates ADH)     Drugs: ADH, nicotine, sulfonylureas , morphine, barbiturates, NSAIDs, acetaminophen, carbamazepine , phenothiazines , tricyclic antidepressants, colchicine , clofibrate , cyclophosphamide , isoproterenol , tolbutamide , vincristine , monoamine oxidase inhibitor     Water intoxication    Glucocorticoid deficiency Positive pressure ventilation     Porphyria      Essential (reset osmostat or sick cell syndrome—usually in the elderly)

9. Diagnostic Criteria for Syndrome of Inappropriate Secretion of ADH Hypotonic hyponatremia Inappropriately elevated urine osmolality (usually >200 mOsm /kg) Elevated urine [Na + ] (typically > 20 mEq /L) Clinical euvolemia Normal adrenal, renal, cardiac, hepatic, and thyroid function Correctable with water restriction

10. Total Body [Na + ] Deficit = (desired plasma [Na + ] － measured plasma [Na + ]) ×TBW

11. Emergency Treatment of Severe Hyponatremia Although specific or general treatment of hyponatremia for the condition discussed may be initiated in the ED, there is generally little urgency to address the hyponatremia immediately when [Na + ] is 120 mEq /L. If hyponatremia is severe (<115 mEq /L or when the patient is symptomatic ), treatment should be initiated .

12. Emergency Treatment of Severe Hyponatremia Situations that warrant consideration of emergent treatment are hypovolemic patients and patients in extremis, (e.g., mental status changes or coma). In hypovolemic patients, the [Na + ] deficit should be calculated and replaced with normal saline solution. Urine electrolytes are useful only before beginning treatment and therefore should be collected in the ED. The rise in [Na + ] should be no greater than 0.5 to 1.0 mEq /L per hour.

13. Reference Fluids and Electrolytes, Tintinalli‘s Emergency Medicine 2010: 117-121 Hyponatremia , NEJM 2000; 342:1581-158 Hypertonic and hypotonic Conditions, The ICU Book 2007: 595-602