Fast Five Quiz: Hyponatremia Essentials

Romesh Khardori, MD, PhD


October 14, 2019

The recommendations for treatment of hyponatremia rely on the current understanding of CNS adaptation to an alteration in serum osmolality. In the setting of an acute fall in the serum osmolality, neuronal cell swelling occurs owing to the water shift from the extracellular space to the intracellular space (ie, Starling forces). Therefore, correction of hyponatremia should take into account the limited capacity of this adaptation mechanism to respond to acute alteration in the serum tonicity, because the degree of brain edema and consequent neurologic symptoms depend as much on the rate and duration of hypotonicity as they do on its magnitude.

A panel of US experts on hyponatremia issued guidelines on the diagnosis, evaluation, and treatment of hyponatremia. For treatment of symptomatic patients with acute hyponatremia (ie, with a known duration < 24-48 hours), the panel recommended urgent correction by 4-6 mmol/L to prevent brain herniation and neurologic damage from cerebral ischemia. Recommended treatment of acute hyponatremia varies by symptom severity, as follows:

  • Severe symptoms: 100 mL of 3% NaCl infused intravenously over 10 minutes × 3 as needed

  • Mild to moderate symptoms, in patients at low risk for herniation: 3% NaCl infused at 0.5-2 mL/kg/h

To avoid ODS in patients with chronic hyponatremia (known duration > 48 hours), the recommendations include the following:

  • Minimum correction of serum sodium by 4-8 mmol/L per day, with a lower goal of 4-6 mmol/L per day if the risk for ODS is high

  • For patients at high risk for ODS: maximum correction of 8 mmol/L in any 24-hour period

  • For patients at normal risk for ODS: maximum correction of 10-12 mmol/L in any 24-hour period or 18 mmol/L in any 48-hour period

For patients with SIADH, fluid restriction (with a goal of 500 mL/day below the 24-hour urine volume) is generally first-line therapy, but pharmacologic treatment should be strongly considered if the patient's urinary parameters indicate low renal electrolyte-free water excretion or if the serum sodium concentration does not correct after 24-48 hours of fluid restriction. Pharmacologic options include demeclocycline (off-label use), urea, and vaptans. Vaptans should not be used in hypovolemic hyponatremia, or in conjunction with other treatments for hyponatremia.

Read more about the treatment of hyponatremia.


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