What is hyponatremia?

From the Guidelines

Hyponatremia is a condition characterized by a low sodium level in the blood, typically defined as a serum sodium concentration of less than 135 mmol/L.

Causes and Types of Hyponatremia

• Hyponatremia can be classified into three main types: hypovolemic, euvolemic, and hypervolemic, depending on the patient's volume status 1.
• In patients with liver cirrhosis, hyponatremia is often caused by dilutional hyponatremia, where there is an excess of water in the body relative to sodium 1.

Clinical Significance and Treatment

• Hyponatremia is associated with a poor prognosis and multiple complications, including seizures, coma, and central pontine myelinolysis 1.
• Treatment of hyponatremia depends on the underlying cause and severity of the condition, and may involve fluid restriction, plasma volume expansion with saline solution, and correction of the causative factor 1.
• In patients with severe hyponatremia, hypertonic sodium chloride administration may be considered, but requires close attention to avoid excessive correction and potential complications 1.
• Aquaretic drugs, such as conivaptan and tolvaptan, may also be used to treat hyponatremia, but their use is limited by potential side effects and requires careful monitoring 1.

From the Research

Definition of Hyponatremia

• Hyponatremia is defined as a serum sodium level of less than 135 mEq/L 2
• It is the most common electrolyte disorder, affecting approximately 5% of adults and 35% of hospitalized patients 2
• Hyponatremia is often caused by water retention, rather than a true sodium deficiency 3

Symptoms and Signs of Hyponatremia

• Symptoms and signs of hyponatremia can range from mild and nonspecific (such as weakness or nausea) to severe and life-threatening (such as seizures or coma) 2
• The severity of symptoms depends on the rapidity of development, duration, and severity of hyponatremia 2
• Mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 2

Diagnosis and Treatment of Hyponatremia

• The diagnosis of hyponatremia involves differentiating hypotonic from nonhypotonic hyponatremia, and further differentiating on the basis of urine osmolality, urine sodium level, and volume status 4
• The treatment for hyponatremia is chosen based on duration and symptoms, with acute or severely symptomatic hyponatremia requiring a bolus of hypertonic saline 4
• Fluid restriction remains the first-line treatment for most forms of chronic hyponatremia, with therapy to increase renal free water excretion often necessary 4
• Vasopressin receptor antagonists, urea, and loop diuretics can be used to increase renal free water excretion, but the choice of treatment depends on the underlying cause and severity of hyponatremia 2, 4

Complications of Hyponatremia

• Overly rapid correction of hyponatremia can result in osmotic demyelination, a rare but severe neurological condition that can cause parkinsonism, quadriparesis, or even death 2, 5, 3
• The rate of correction of sodium concentration in chronic and profound hyponatremia should not exceed 10 mmol/L during the first 24 hours, and 18 mmol/L during the first 48 hours 3