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Diagnosis and Management of Sodium Disorders: Hyponatremia and Hypernatremia

Nathaniel E. Miller, MD
David Rushlow, MD, MBOE
Stephen K. Stacey, DO

American Family Physician. 2023;108(5):476-486.

Author disclosure: No relevant financial relationships.

Hyponatremia and hypernatremia are electrolyte disorders that can be associated with poor outcomes. Hyponatremia is considered mild when the sodium concentration is 130 to 134 mEq per L, moderate when 125 to 129 mEq per L, and severe when less than 125 mEq per L. Mild symptoms include nausea, vomiting, weakness, headache, and mild neurocognitive deficits. Severe symptoms of hyponatremia include delirium, confusion, impaired consciousness, ataxia, seizures, and, rarely, brain herniation and death. Patients with a sodium concentration of less than 125 mEq per L and severe symptoms require emergency infusions with 3% hypertonic saline. Using calculators to guide fluid replacement helps avoid overly rapid correction of sodium concentration, which can cause osmotic demyelination syndrome. Physicians should identify the cause of a patient's hyponatremia, if possible; however, treatment should not be delayed while a diagnosis is pursued. Common causes include certain medications, excessive alcohol consumption, very low-salt diets, and excessive free water intake during exercise. Management to correct sodium concentration is based on whether the patient is hypovolemic, euvolemic, or hypervolemic. Hypovolemic hyponatremia is treated with normal saline infusions. Treating euvolemic hyponatremia includes restricting free water consumption or using salt tablets or intravenous vaptans. Hypervolemic hyponatremia is treated primarily by managing the underlying cause (e.g., heart failure, cirrhosis) and free water restriction. Hypernatremia is less common than hyponatremia. Mild hypernatremia is often caused by dehydration resulting from an impaired thirst mechanism or lack of access to water; however, other causes, such as diabetes insipidus, are possible. Treatment starts with addressing the underlying etiology and correcting the fluid deficit. When sodium is severely elevated, patients are symptomatic, or intravenous fluids are required, hypotonic fluid replacement is necessary.

Sodium abnormalities are common electrolyte disorders associated with significant morbidity and mortality. Abnormalities include hyponatremia (serum sodium concentration less than 135 mEq per L) and the less common hypernatremia (greater than 145 Eq per L). Understanding the pathophysiology of these conditions can be helpful in diagnosis and treatment.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating Comments
Patients with a sodium concentration of less than 125 mEq per L and moderate or severe symptoms can be treated with bolus or continuous infusions of 3% hypertonic saline without increased risk of osmotic demyelination syndrome or mortality. Bolus infusion improves sodium concentration more quickly with less overcorrection.1,2,10,13 B Consensus guidelines, expert opinion, one randomized controlled trial
Sodium concentration should be monitored after each hypertonic saline bolus and every six hours during the first 24 hours of treatment for severe symptomatic hyponatremia.1,2,10 C Consensus guidelines, expert opinion
Sodium correction should be limited to 8 mEq per L over 24 hours in patients with chronic hyponatremia who are at increased risk of osmotic demyelination syndrome. For patients without risk factors, sodium correction should be limited to 12 mEq per L over 24 hours and 18 mEq per L over 48 hours to minimize the risk of osmotic demyelination syndrome.2 C Consensus guidelines
In the absence of severe hyponatremia, the next steps in the management of hypotonic hyponatremia (true hyponatremia) are based on whether the patient is hypovolemic, euvolemic, or hypervolemic.2,10 C Consensus guidelines
Hypernatremia in adults can be corrected at a rate of 12 mEq per L over 24 hours; however, if this rate is exceeded, therapeutically increasing the serum sodium again should be avoided.30,37 B Observational study, expert opinion

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.

NATHANIEL E. MILLER, MD, is a family medicine residency core faculty member and an assistant professor in the Department of Family Medicine at Mayo Clinic, Rochester, Minn.

DAVID RUSHLOW, MD, MBOE, is an assistant professor in and chair of the Midwest Department of Family Medicine at Mayo Clinic.

STEPHEN K. STACEY, DO, is the director of osteopathic education and an assistant professor of family medicine at the La Crosse (Wis.)-Mayo Family Medicine Residency, Mayo Clinic Health System.

Address correspondence to Stephen K. Stacey, DO, Mayo Clinic, 815 10th St. S, La Crosse, WI 54601 (stacey.stephen@mayo.edu). Reprints are not available from the authors.

Author disclosure: No relevant financial relationships.

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