What are the causes and symptoms of hyponatremia?

From the Guidelines

Hyponatremia is a condition characterized by abnormally low sodium levels in the blood, specifically below 135 mEq/L, and its causes include excessive water intake, certain medications, medical conditions, and syndrome of inappropriate antidiuretic hormone secretion (SIADH), with symptoms varying based on severity and rate of development. The causes of hyponatremia can be divided into several categories, including:

• Excessive water intake
• Certain medications, such as diuretics, antidepressants, and anticonvulsants
• Medical conditions, including heart failure, kidney disease, liver cirrhosis, and adrenal gland insufficiency
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
• Hormonal changes
• Excessive sweating or vomiting without adequate sodium replacement

Symptoms of hyponatremia vary based on the severity and rate of development, and can include:

• Headache
• Nausea
• Muscle cramps
• Fatigue
• Confusion
• Seizures
• Coma
• Death if left untreated

According to the most recent and highest quality study 1, hyponatremia is common in patients with advanced cirrhosis and has been arbitrarily defined as serum sodium concentration lower than 130 mmol/L. However, reductions below 135 mmol/L should also be considered. Patients with hyponatremia have a poor prognosis, as it is associated with increased mortality and morbidity, particularly neurological complications, and reduced survival after liver transplantation.

Treatment of hyponatremia depends on the cause, severity, and rate of development, ranging from fluid restriction for mild cases to intravenous sodium solution for severe or acute cases. The first step in the treatment of hyponatremia is to distinguish the type of hyponatremia, with fluid resuscitation needed for hypovolemic hyponatremia and discontinuation of intravenous fluid therapy and free water restriction considered for hypervolemic hyponatremia 1. Frequent monitoring is necessary when correcting the serum sodium concentration to avoid excessive correction and potential complications such as central pontine myelinolysis or seizures.

In cases of hypervolemic hyponatremia, fluid restriction (1-1.5 L/day) should be considered if the serum sodium concentration is below 120-125 mmol/L and neurologic symptoms are present. The administration of hypertonic sodium chloride allows a temporary elevation in the serum sodium concentration and symptom relief after administration, but this treatment requires close attention because edema and ascites can be worsened. Vaptans, such as tolvaptan, have been shown to be effective in improving serum sodium concentration in patients with hypervolemic hyponatremia, particularly in those with cirrhosis, heart failure, or SIADH 1.

From the Research

Causes of Hyponatremia

• Hyponatremia can result from various causes, including water retention, certain medications, excessive alcohol consumption, very low-salt diets, and excessive free water intake during exercise 2.
• It can also be caused by elevated levels of arginine vasopressin (AVP) hormone, which can occur in clinical conditions such as syndrome of inappropriate secretion of AVP, volume depletion, postoperative states, heart failure, cirrhosis, neuroendocrine disorders, and trauma 3.
• Hyponatremia can be classified into three types: hypovolemic, euvolemic, and hypervolemic, each with different underlying causes and treatment approaches 4, 5.

Symptoms of Hyponatremia

• Symptoms of hyponatremia can range from mild and nonspecific, such as weakness, nausea, and headache, to severe and life-threatening, such as seizures, coma, and brain herniation 6, 2.
• The severity of symptoms depends on the rapidity of development, duration, and severity of hyponatremia, as well as the patient's volume status 3, 5.
• Mild chronic hyponatremia can be associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 6.
• Severe hyponatremia can cause delirium, confusion, impaired consciousness, ataxia, and seizures, and requires emergency treatment with 3% hypertonic saline 2.

Classification of Hyponatremia

• Hyponatremia can be classified as mild (130-134 mEq/L), moderate (125-129 mEq/L), or severe (<125 mEq/L) based on the serum sodium concentration 2.
• It can also be classified based on the patient's volume status as hypovolemic, euvolemic, or hypervolemic, each with different treatment approaches 4, 5.
• The classification of hyponatremia is crucial in guiding treatment and management, as different types of hyponatremia require different treatment strategies 3, 2.