From the Guidelines
For patients with hyponatremia due to water deficit, the primary goal is to correct the serum sodium level gradually, without exceeding 8-10 mEq/L in 24 hours, to prevent osmotic demyelination syndrome, as recommended by the 2018 clinical practice guidelines for liver cirrhosis 1. To calculate the water deficit in hyponatremia, the formula: Water deficit = Total body water × [(current serum sodium/desired serum sodium) - 1] can be used. Total body water is estimated as 0.6 × body weight in kg for men and 0.5 × body weight in kg for women.
- For example, in a 70 kg man with a serum sodium of 120 mEq/L who needs correction to 135 mEq/L, the water deficit would be 42 L × [(120/135) - 1] = -4.7 L, indicating excess water.
- Correction should be gradual, typically not exceeding 8-10 mEq/L in 24 hours to prevent osmotic demyelination syndrome, as excessive correction of more than 9 mmol/L within 24 hours is associated with central pontine myelinolysis or seizures 1.
- For symptomatic hyponatremia, initial correction with 3% hypertonic saline at 1-2 mL/kg/hr may be needed, with frequent monitoring of serum sodium levels.
- The underlying cause of hyponatremia must also be addressed, whether it's SIADH, heart failure, cirrhosis, or medication-induced, and fluid restriction is often necessary, with the specific amount determined by the severity of hyponatremia and the patient's clinical condition, such as discontinuation of intravenous fluid therapy and free water restriction, or fluid restriction (1-1.5 L/day) if the serum sodium concentration is below 120-125 mmol/L and neurologic symptoms are present 1.
From the Research
Hyponatremia and Water Deficit
- Hyponatremia is defined as a serum sodium level of less than 135 mEq/L and is the most common electrolyte disorder, affecting approximately 5% of adults and 35% of hospitalized patients 2.
- It is often caused by water retention, and even mild cases can be associated with increased hospital stay and mortality 2.
- Symptoms of hyponatremia can range from mild and nonspecific, such as weakness or nausea, to severe and life-threatening, such as seizures or coma 2, 3.
Diagnosis and Management
- When evaluating patients with hyponatremia, clinicians should categorize them according to their fluid volume status (hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia) 2, 3.
- The approach to managing hyponatremia should consist of treating the underlying cause, and urea and vaptans can be effective treatments for certain cases, such as the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure 2.
- Hypertonic saline is reserved for patients with severely symptomatic hyponatremia, and its use should be guided by careful monitoring of serum sodium levels to avoid overly rapid correction and complications such as osmotic demyelination 2, 3, 4.
Treatment Considerations
- The treatment of hyponatremia depends on the severity of symptoms, the underlying cause, and the patient's fluid volume status 3, 5.
- For patients with mild hyponatremia, treatment may involve restricting free water consumption or using salt tablets or intravenous vaptans 3.
- In cases of severe hyponatremia, emergency infusions with 3% hypertonic saline may be necessary to rapidly correct serum sodium levels and prevent neurological complications 3, 4.
- Careful administration and monitoring of serum sodium levels are crucial to avoid overcorrection and complications such as osmotic demyelination 6, 4.