Diagnosis and Management of Hyponatremia

Hyponatremia is defined as a serum sodium concentration <>

Signs and Symptoms of Hyponatremia:

Most patients with hyponatremia are asymptomatic, and when symptoms appear they are usually nonspecific. They include:

• Nausea and malaise are the earliest findings if Na <>

• Headache, lethargy and obtundation

• Seizures, coma and respiratory arrest if Na <>

What are the causes of hyponatremia?

Hypertonic Hyponatremia

• Factitious Hyponatremia due to Hyperglycemia or Administration of Mannitol

Hypotonic hyponatremia (most common)

• Hypervolemic hypotonic hyponatremia: caused by congestive heart failure, liver cirrhosis, renal failure or nephrotic syndrome

• Euvolemic hypotonic hyponatremia: Psychogenic polydipsia, Alcoholism, Hypokalemia, SIADH, Hypothyroidism, Thiazide diuretics

• Hypovolemic hypotonic hyponatremia: GI losses, Fluid sequestration, Insensible losses e.g. seat, burns, Na wasting nephropathy, Addison’s disease, Postobstructive diuresis

Hyponatremia with Normal Plasma osmolality

• Pseudohyponatremia due to Hyperlipidemia or Hyperproteinemia

How do you diagnose hyponatremia?

History:

• Inquire about any history of fluid loss e.g. vomiting, diarrhea, diuretic therapy: history consistent with one of the causes of SIADH e.g. Small Cell Carcinoma or Central Nervous system disease

Physical Exam:

• Observe for signs of extracellular volume depletion e.g. decreased skin turgor and low jugular venous pressure; Signs of peripheral edema and/or ascites which can be due to congestive heart failure, cirrhosis, or renal failure; Signs or symptoms suggestive of adrenal sufficiency or hypothyroidism

Laboratory Tests:

• Plasma Osmolality, Urine Osmolality and Urine Sodium Concentration

How do you treat hyponatremia?

• Determine if immediate treatment is required based on the presence of symptoms, the degree of hyponatremia, whether the condition is acute (<48hrs)>

• Determine the most appropriate method of correcting the hyponatremia

• For acute severe hyponatremia associated with neurologic symptoms should be treated urgently with hypertonic saline at a correction rate that does not exceed 1-2 mmol per L per hour, and normo/hypernatremia should be avoided in the first 48 hours

• For chronic hyponatremia, rapid correction should be avoided because it can lead to central pontine myelinolysis. In most cases of chronic asymptomatic hyponatremia, removing the underlying cause of the hyponatremia is adequate treatment. Otherwise, fluid restriction (less than 1 to 1.5 L per day) is the mainstay of treatment. The combination of a loop diuretic with high-sodium diet may be required to achieve an adequate response in patients with chronic SIADH.

• Demeclocycline in a dosage of 600 – 1,200 mg daily can be used to induce a negative free-water balance by causing nephrogenic diabetes insipidus.

• Arginine vasopressin receptor antagonists have been shown to be useful in patients with chronic hyponatremia.

Algorithm for Evaluation of hypotonic hyponatremia

References

1. Goh, K.P., Management of Hyponatremia, American Family Physician 2004; 69:2387-94.

2. Kugler, J.P., and Hustead, T., Hyponatremia and Hypernatremia in the Elderly, American Family Physician 2000; 61:3623-30.

3. Up to Date:

   1. Manifestation of hyponatremia and hypernatremia

   2. Treatment of hyponatremia

   3. Causes of hyponatremia

   4. Diagnosis of hyponatremia

Category: Medicine Notes