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Acute vs Chronic Hyponatremia​​​

Defining the duration of hyponatremia

An important step in the treatment of patients with hyponatremia is to determine whether their disease is acute or chronic, defined as duration of <48 hours or ≥48 hours.1

Acute symptomatic hyponatremia

Acute symptomatic hyponatremia is defined as hyponatremia that develops in less than 48 hours. When the serum sodium level falls below 125 mEq/L, there is increased risk for neurologic symptoms secondary to brain cell swelling.1

In acute severe and rapidly developing hyponatremia, treatment should begin as s​oon as the problem is identified. The goal of treatment is to increase the serum sodium level by 1.5 to 2 mEq/L/hour until symptoms subside or until the sodium concentration is >118 to 120 mEq/L, with the primary focus to minimize the risk of seizure. Even in symptomatic patients, the sodium level should not be increased by >12 mEq/L in the first 24 hours, or by >18 mEq/L in the first 48 hours, to avoid osmotic demyelination syndrome (ODS).1

When patients become asymptomatic and sodium levels rise above 118 mEq/L, correction should be slowed to no more than 8 mEq/L in 24 hours to achieve the target sodium concentration. In all cases, close and frequent monitoring of serum sodium and electrolytes is mandatory until sodium levels increase and symptoms of hyponatremia resolve.1

Chronic symptomatic hyponatremia*

In hyponatremia of unknown duration, sodium correction should be managed cautiously because of brain adaptation to prolonged hyponatremia. In patients presenting with severe symptoms, treatment should be similar to that for acute symptomatic hyponatremia.1

Careful monitoring is critical because of increased risk of irreversible osmotic demyelination. Correction should be limited to no more than 10 to 12 mEq/L during the first 24 hours of treatment and <6 mEq/L/day subsequently. In patients presenting with mild to moderate symptoms, slower correction is required. Once the desired correction is achieved, fluid restriction may be employed.1

Chronic asymptomatic hyponatremia*

When treating asymptomatic hyponatremia, the goal is to prevent further decreases in serum sodium levels and to keep levels as close to normal as possible.1

​*Limit duration of therapy with SAMSCA to 30 days.