Does my patient have hyponatremia?

Hyponatremia or sodium (Na) <135 mEq/L represents a relative excess of water in relation to Na.

Hyponatremia can be acute or chronic.

·         Acute: <48 hours. Results from parenteral IV administration in postoperative patients (who have ADH hypersecretion associated with surgery) and from self-induced water intoxication (as in, for example, competitive runners, psychotic patients with extreme polydipsia and users of ecstasy).

·         Chronic: > 48 hours

Hyponatremia can be categorized as mild, moderate or severe.

·         Mild hyponatremia: 130-134 mEq/L

·         Moderate hyponatremia: 120-129 mEq/L

·         Severe hyponatremia: Na <120 mEq/L

The symptoms of mild to moderate hyponatremia are relatively nonspecific and include headache, fatigue, lethargy, nausea, vomiting, dizziness, gait disturbances, forgetfulness, confusion, and muscle cramps.

The symptoms of severe hyponatremia include seizures, obtundation, coma, and respiratory arrest.

How do I know that my patient has hyponatremia? Look for the following:

·         Is hyperglycemia present? Corrected serum sodium (Na): The sodium level will fall by 2 mEq/L for every 100 mg/100 mL rise in glucose level.

·         Rule out pseudohyponatremia: Lipemic serum, severe obstructive jaundice, or a known plasma cell dyscrasia

·         Rule out lab artefact: Na measured with flame photometry

·         Recent prostate surgery: utilizing large volumes of electrolyte-poor irrigation fluid (or intrauterine procedures)

·         Recent drugs: mannitol, glycerol, or intravenous immune globulin (isotonic or hypertonic hyponatremia).

·         Hypotonic hyponatremia: Severely reduced glomerular filtration rate (GFR) and thiazide (or thiazide-type) diuretics

·         Is edema or ascites present? Advanced heart failure or cirrhosis

·         Non-edematous patients with hypotonic hyponatremia: Euvolemic or hypovolemic.

Treatment

Patients with acute hyponatremia, most patients with severe hyponatremia (< 120) and most patients with symptomatic hyponatremia should be treated in hospital settings that allow frequent assessments of the patient’s neurologic condition

Four treatment goals: to prevent further declines in the serum sodium concentration, to decrease intracranial pressure in patients at risk for developing brain herniation, to relieve symptoms of hyponatremia and to avoid excessive correction of hyponatremia in patients at risk for osmotic demyelination syndrome

·         Goal of initial therapy: Raise Na by 4 to 6 mEq/L in a 24-hour period.

·         Acute hyponatremia or severe symptoms: This goal in < 6 hours

·         Chronic, severe hyponatremia, the maximum rate of correction should be 8 mEq/L in any 24-hour period.

Clinical situations

·         Asymptomatic acute hyponatremia Na < 130 mEq/L: 50 mL bolus of 3% hypertonic saline to prevent the serum sodium from falling further. Remeasure Na hourly to determine the need for additional therapy. Do not give these patients hypertonic saline if the hyponatremia is already autocorrecting due to a water diuresis.

·         Symptomatic acute hyponatremia Na < 130 mEq/L: Symptoms that might be due to increased intracranial pressure (seizures, obtundation, coma, respiratory arrest, headache, nausea, vomiting, tremors, gait or movement disturbances, or confusion) with a 100 mL bolus of 3% saline, followed, if symptoms persist, with up to two additional 100 mL doses (to a total dose of 300 mL) over the course of 30 minutes.

·         Chronic hyponatremia and Na < 130 mEq/L

Severe symptoms of hyponatremia or in those with known intracranial pathology (such as recent traumatic brain injury, recent intracranial surgery or hemorrhage, or an intracranial neoplasm or other space-occupying lesion): Treat with a 100 mL bolus of 3% saline followed, if symptoms persist, by up to two additional 100 mL doses (to a total dose of 300 mL).

Asymptomatic or have mild to moderate symptoms and who have moderate hyponatremia (120-129 mEq/L): Take only those measures that are broadly applicable to all hyponatremic patients (identify and discontinue drugs that could be contributing to hyponatremia; identify and, if possible, reverse the cause of hyponatremia; and limit further intake of water).

Asymptomatic or have mild to moderate symptoms and who have severe hyponatremia (<120 mEq/L): Give IV 3% saline beginning at a rate of 15 to 30 mL/hour. In addition, among those with reversible causes of hyponatremia who are likely to develop a water diuresis during the course of therapy, or in those who are at high risk of developing osmotic demyelination syndrome (ODS), desmopressin (dDAVP) should be initiated simultaneously to prevent overly rapid correction.

Follow up

·         Hypertonic saline should be discontinued once the daily correction goal of 4 to 6 mEq/L has been achieved.

·         Fluid restriction to below the level of urine output is indicated for the treatment of symptomatic or severe hyponatremia in edematous states (such as heart failure and cirrhosis), syndrome of inappropriate ADH (SIADH), advanced renal impairment, and primary polydipsia. In patients with a highly concentrated urine (e.g., 500 mOsmol/kg or higher), fluid restriction alone may be insufficient to correct hyponatremia.

·         Depending upon the etiology: Loop diuretics, oral salt tablets, urea, K supplementation, or vasopressin receptor antagonists (tolvaptan for up to 30 days, not in liver disease).

Oral salt

9 g of oral salt provides a similar quantity of sodium as 1 L of isotonic saline (154 mEq) but without any water; 1 g of oral salt is equivalent to 35 mL of 3 percent saline. Oral salt tablets should not be given to edematous patients (e.g., those with heart failure, cirrhosis).

Dr KK Aggarwal

Padma Shri Awardee

President Elect Confederation of Medical Associations in Asia and Oceania   (CMAAO)

Group Editor-in-Chief IJCP Publications

President Heart Care Foundation of India

Past National President IMA