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What causes hyponatremia?

Sweeney, Judy RN, MSN


I'm caring for a 74-year-old man who had surgery for bladder cancer. He's N.P.O., receiving I.V. 0.45% sodium chloride solution, and he has an abdominal drain. He became confused and increasingly lethargic during my shift. When I notified the primary care provider, she ordered stat serum electrolytes. What was going on?—L.W., IDAHO

Judy Sweeney, RN, MSN, replies: Hyponatremia is the most common electrolyte imbalance affecting hospitalized patients. Your patient was at particular risk because of his age, N.P.O. status, wound drainage, and the hypotonic I.V. fluid he was receiving.

Sodium helps control interstitial and intravascular fluid volume. The normal serum sodium level is 135 to 145 mEq/liter. A patient experiences signs and symptoms of hyponatremia when serum sodium falls below 125 mEq/liter. Causes of hyponatremia include:

  • sodium loss, as from diuretics, vomiting, or wound drainage
  • decreased sodium intake, as with N.P.O. status
  • water gain, which can occur if the patient receives too much of a hypotonic I.V. fluid such as 0.45% sodium chloride solution.

Signs and symptoms of hyponatremia occur when a drop in serum sodium pulls water into cells. Common signs and symptoms of hyponatremia include headache, confusion, lethargy, muscle weakness, and nausea and can be mistaken for complications from anesthesia, analgesia, or hypoxia.

Treating hyponatremia depends on the underlying cause, severity, and patient acuity. For example, if your patient is volume depleted, expect to administer 0.9% sodium chloride solution. If the patient's sodium level is below 120 mEq/liter and he has severe neurologic dysfunction, expect to administer hypertonic 3% sodium chloride solution to slowly raise his sodium level. Monitor him closely because correcting hyponatremia too quickly can also cause serious problems.

Judy Sweeney is an associate professor of nursing at Vanderbilt University School of Nursing in Nashville, Tenn. Clinical Queries is coordinated by Joan E. King, RN, C, ACNP, ANP, PhD, program director for the acute care nurse practitioner program at Vanderbilt University.

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      © 2005 Lippincott Williams & Wilkins, Inc.