From the Guidelines
Hyponatremia is primarily caused by an imbalance of water and sodium in the body, often categorized into hypovolemic, euvolemic, and hypervolemic types, with the underlying pathophysiology typically involving disruption of water homeostasis through inappropriate ADH secretion or action, as noted in the guidelines on the management of ascites in cirrhosis 1. The aetiology of hyponatremia can be complex, involving various factors such as:
- Hypovolemic hyponatremia, which occurs due to sodium and water loss with inadequate water replacement, seen in conditions like vomiting, diarrhea, excessive sweating, diuretic use, and adrenal insufficiency.
- Euvolemic hyponatremia, resulting from water retention without sodium excess, commonly caused by the syndrome of inappropriate antidiuretic hormone secretion (SIADH), which can be triggered by CNS disorders, pulmonary diseases, malignancies, and medications like SSRIs, carbamazepine, and certain antipsychotics.
- Hypervolemic hyponatremia, which occurs when both sodium and water are retained, but water retention exceeds sodium retention, seen in heart failure, cirrhosis, and nephrotic syndrome. According to the guidelines on the management of ascites in cirrhosis 1, the treatment of hyponatremia depends on the underlying cause, with hypovolemic hyponatremia requiring expansion of plasma volume with normal saline and correction of the causative factor, while hypervolemic hyponatremia requires attainment of a negative water balance, which can be achieved through fluid restriction and the use of vaptans, as recommended in the diagnosis, evaluation, and management of ascites, spontaneous bacterial peritonitis and hepatorenal syndrome: 2021 practice guidance by the American Association for the Study of Liver Diseases 1. The management of hyponatremia should prioritize the correction of the underlying cause, with fluid restriction to 1-1.5 L/day recommended for patients with severe hyponatremia (serum sodium <125 mmol/L) and clinical hypervolemia, as stated in the guidelines on the management of ascites in cirrhosis 1. In addition, the use of vaptans, such as tolvaptan, has been shown to be effective in improving serum sodium concentration in patients with hypervolemic hyponatremia, as noted in the EASL clinical practice guidelines for the management of patients with decompensated cirrhosis 1. Overall, the management of hyponatremia requires a comprehensive approach, taking into account the underlying cause, severity, and clinical context, with the goal of correcting the imbalance of water and sodium in the body, as emphasized in the KASL clinical practice guidelines for liver cirrhosis: ascites and related complications 1.
From the Research
Aetiology of Hyponatremia
Hyponatremia is a common electrolyte disorder that can result from various causes, including:
- Water retention, which is the most common cause 2
- Syndrome of inappropriate antidiuretic hormone secretion (SIADH) 3, 4, 5
- Adrenocortical insufficiency 4
- Hypothyroidism 4
- Psychogenic polydipsia 4
- Certain drugs, such as chemotherapeutics, antipsychotics, and antidepressants 4
- Endurance exercise events 4
- Reset osmostat syndrome (ROS) 4
- Liver cirrhosis, which can lead to hypervolemic hyponatremia 6
- Heart failure, which can also lead to hypervolemic hyponatremia 2, 3
Classification of Hyponatremia
Hyponatremia can be classified into three main types based on the patient's fluid volume status:
- Hypovolemic hyponatremia, which is characterized by a decrease in total body sodium and water 2, 3
- Euvolemic hyponatremia, which is characterized by a normal total body sodium and water, but an excess of water relative to sodium 2, 3, 4, 5
- Hypervolemic hyponatremia, which is characterized by an excess of both sodium and water, but a greater excess of water 2, 3, 6
Pathogenesis of Hyponatremia
The pathogenesis of hyponatremia involves an imbalance between the amount of sodium and water in the body, leading to an excess of water relative to sodium. This can result from: