Hyponatremia[Na] < 135 mEq/L

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

Effects of Hyponatremia on the Brain and Adaptive Responses.

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.

Causes of Hyponatremia

Hypertonic Hyponatremia – Osmotic Pressure >295

Isotonic Hyponatremia– Osmotic Pressure 275 to 295

Hypotonic Hyponatremia– Osmotic Pressure <275

Hypertonic hyponatremia (Posm >295)

Hyperglycemia  

Mannitol excess  

Glycerol therapy

Isotonic (pseudo) hyponatremia (Posm 275–295)

Hyperlipidemia  

Hyperproteinemia (e.g., multiple myeloma, Waldenström macroglobulinemia)

Hypotonic hyponatremia (Posm <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)

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

Total Body [Na+] Deficit

= (desired plasma [Na+]－measured plasma [Na+]) ×TBW

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.

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.

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