From the Guidelines
Hyponatremia is primarily caused by an imbalance of sodium in the body, resulting from excessive water intake, inadequate sodium intake, or impaired water excretion, with common causes including certain medications, medical conditions like heart failure, liver cirrhosis, and kidney disease, as well as hormonal disorders and excessive sweating without proper electrolyte replacement, as noted in studies such as 1 and 1.
Causes of Hyponatremia
The causes of hyponatremia can be multifaceted, involving:
- Excessive water intake that dilutes sodium concentration
- Inadequate sodium intake
- Impaired water excretion due to various medical conditions
- Certain medications like thiazide diuretics, SSRIs, and carbamazepine
- Medical conditions such as heart failure, liver cirrhosis, kidney disease, and SIADH
- Hormonal disorders including adrenal insufficiency and hypothyroidism
- Excessive sweating without proper electrolyte replacement
- Drinking too much water during endurance activities (exercise-associated hyponatremia)
- Severe vomiting or diarrhea that can deplete sodium levels
Mechanisms and Regulation
The body maintains sodium balance through complex interactions between the kidneys, adrenal glands, and brain, particularly through hormones like ADH (antidiuretic hormone) that regulate water retention. When these regulatory mechanisms are disrupted, either through disease processes or external factors like medications, hyponatremia can develop, potentially leading to symptoms ranging from mild (headache, confusion) to severe (seizures, coma) depending on how quickly and severely sodium levels drop, as discussed in 1 and 1.
Clinical Considerations
It's crucial to identify and address the underlying cause of hyponatremia, as treatment strategies vary based on the etiology. For instance, fluid restriction may be beneficial in some cases, while in others, the use of vasopressin antagonists or hypertonic saline may be necessary, as indicated in 1, 1, and 1. The management of hyponatremia requires careful consideration of the patient's clinical status, the severity of the hyponatremia, and the presence of any symptoms, to ensure appropriate and effective treatment, as emphasized in 1.
From the Research
Causes of Hyponatremia
Hyponatremia can be caused by various factors, including:
- Medications, such as thiazide diuretics, vasopressin, and its analogues, chlorpropamide, carbamazepine, antipsychotics, antidepressants, and nonsteroidal anti-inflammatory drugs 2
- The syndrome of inappropriate antidiuretic hormone (SIADH) secretion, which can be ectopic or caused by osmoregulatory defects 3
- Excessive fluid intake, which can be iatrogenic or due to inappropriate thirst 3
- Congestive heart failure, liver cirrhosis, and renal disease, which can cause hypervolemic hyponatremia 4
- Severe burns, gastrointestinal losses, and acute water overload, which can cause hypovolemic hyponatremia 4
- Hyperglycemia, which can cause hyponatremia with a high plasma osmolality 4
- Pseudohyponatremia or the post-transurethral prostatic resection syndrome, which can cause hyponatremia with a normal plasma osmolality 4
- Renal disorders, endocrine deficiencies, reset osmostat syndrome, and SIADH, which can cause high urinary sodium concentration in the presence of low plasma osmolality 4
- Excessive alcohol consumption, very low-salt diets, and excessive free water intake during exercise 5
Classification of Hyponatremia
Hyponatremia can be classified according to the volume status of the patient as:
- Hypovolemic hyponatremia, which is treated with normal saline infusions 5
- Euvolemic hyponatremia, which is treated by restricting free water consumption or using salt tablets or intravenous vaptans 5
- Hypervolemic hyponatremia, which is treated primarily by managing the underlying cause and free water restriction 5