Introduction
Sodium is one of the seven essential minerals the body needs for normal functioning. It maintains normal cell homeostasis (balance and function), fluid and electrolyte balance, and blood pressure (BP). It is a major component of the extracellular fluid (ECF). It maintains the ECF balance by exerting an osmotic pressure. It also plays a pertinent role in nerve-muscle conduction and nutrient transport through plasma membranes. The normal plasma concentration of sodium is 135 to 145 milliequivalents/liter (mEq/L). Hyponatremia (low serum sodium) and hypernatremia (high serum sodium) are the most common sodium disorders.
What Is Hyponatremia and How Is it Managed?
Hyponatremia happens when the serum sodium level is less than 135 mEq/L. It is a common electrolyte abnormality in which the total body water (TBW) exceeds the sodium content. Hyponatremia is the most frequent electrolyte condition in 20 to 35 percent of hospitalized patients. It is more common in older individuals with multiple coexisting conditions, medications, and lack of food and water access. The causes of hyponatremia depend upon the ECF volume. Hyponatremia is divided into the hypovolemic, euvolemic, or hypervolemic types.
Hypovolemic Hyponatremia: It is characterized by decreased TBW and sodium levels. It happens in excessive vomiting, diarrhea, use of diuretics (a BP medication), and mineralocorticoid deficiency. Mineralocorticoids are steroid hormones that manage salt and water balance in the body.
Treatment: It includes isotonic saline administration and sodium chloride tablets. Isotonic saline has a similar sodium concentration to the serum. Further, any underlying condition must be treated.
Euvolemic Hyponatremia: TBW is increased with normal sodium levels. It occurs in medication use, Addison’s disease (a condition in which the adrenal glands do not produce adequate hormones), hypothyroidism (a condition in which the thyroid gland produces less thyroxine hormone), and a high fluid intake. The medications include Carbamazepine (an anti-anxiety drug), Cyclophosphamide (an immunosuppressant), and Nicotine (a stimulant found in cigarette smoke).
Treatment: The treatment is fluid restriction. However, salt and protein intake should not be limited. Other treatments include hypertonic saline (higher sodium concentration than serum) and vasopressin antagonists (vasopressin is a hormone secreted by the hypothalamus that reduces water excretion). For example, Vaptans (Conivaptan and Tolvaptan) are the vasopressin antagonists approved for severe euvolemic hyponatremia. However, their use is debated. Studies have found that Tolvaptan reduces the associated disease and death rates. Lixivaptan is another vasopressin antagonist in clinical trials. Hence, it lacks Food and drug administration (FDA) approval. Doctors should also treat the underlying medical condition.
Hypervolemic Hyponatremia: The TBW increases as compared to sodium levels. It happens in renal failure (acute and chronic) and extra-renal causes such as congestive heart failure (a condition in which the heart does not work properly) and cirrhosis (a liver disease). It may also be doctor-induced (iatrogenic).
Treatment: Diuretics, angiotensin-converting enzyme inhibitors (ACE-I), and beta-blockers (all are BP medications) are given. Fluid restriction is important. Similar to euvolemic hyponatremia, vaptans are used. Dialysis is sometimes needed to correct renal conditions.
Pseudohyponatremia: This is an uncommon laboratory abnormality. It is caused by serum sodium displacement due to osmosis. It mostly happens in hyperglycemia (increased blood sugar) as the increased sugar forces the water into the ECF, which causes an apparent decrease in sodium.
Diagnosis of Hyponatremia: The diagnostic workup involves a thorough history and physical examination. Various medications, such as diuretics and Carbamazepine, should be reviewed. Patients should also stop alcohol and illicit drug intake.
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Laboratory investigations include a complete metabolic profile and urinary sodium levels. Hyponatremia is classified as acute or chronic. Symptoms depend upon the extent of hyponatremia.
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Mild to moderate hyponatremia patients have minimal symptoms such as lethargy and dizziness.
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Acute hyponatremia happens within two days. For example, if the sodium level is 125 to 130 mEq/L, acute hyponatremia leads to brain swelling, confusion, nausea, and malaise. However, when the sodium level reaches 110 mEq/L, headache, fits, coma, and death may occur.
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Increased thirst, muscle cramps, fainting, and altered mental status require immediate intervention.
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In severe symptomatic hyponatremia, 3 % saline is recommended. The doctors must repeat the dose if symptoms do not resolve. Then, serum sodium levels should be checked, and doctors can switch to isotonic saline.
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The treatment should be stopped if the symptoms cease or the sodium level reaches 120 mEq/L.
Prognosis of Hyponatremia: The prognosis (disease progression) of hyponatremia depends on the disease severity. A poor prognosis is found in elderly patients and patients with acute or severe hyponatremia.
What Is Hypernatremia and How Is it Managed?
Hypernatremia is the serum sodium concentration of more than 145 mEq/L. TBW loss, as compared to sodium loss, is the most common cause. The condition is called hypovolemia. It can be seen in vomiting, excessive sweating, and burns. Excessive sweating is seen in vigorous exercise, fever, or exposure to high heat. Hypernatremia is seen mainly in infants and older individuals. Inadequate water replacement or ineffective breastfeeding is most common in infants. Hypernatremia is also divided into hypovolemic, euvolemic, and hypervolemic types.
Signs and Symptoms: Signs and symptoms include water loss and dehydration. The central nervous system involvement occurs when the sodium levels are more than 160 mEq/L. Irritability, agitation, lethargy, and coma ensue. Advanced hypernatremia can cause muscle twitching and spasms.
Diagnosis: The diagnosis of hypernatremia is made through blood investigations. Urine tests also check the level of sodium in urine. The advantages of urine and blood tests are the minimally invasive nature and rapid diagnosis.
Management: It is managed by a multidisciplinary team of an emergency physician, endocrinologist, nurse, and primary care physician. The treatment includes serum sodium and fluid correction. Serum sodium levels should be periodically monitored.
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Fluids should be given either orally or via a feeding tube.
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Moderate hypernatremia is corrected by intravenous (into the vein) hypotonic fluid administration. Isotonic fluid resuscitation is important in patients with severe dehydration before any other step.
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The important point is that the correction should be at most 12 mEq/L in one day. It is because a rapid correction can lead to brain swelling as water moves into the brain cells. It can also precipitate seizures (fits). Therefore, close monitoring is essential every 2 hours of treatment.
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Chronic hypernatremia is corrected at 0.5 mEq/L per hour.
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Hypernatremia outcome is very good if the condition is corrected early.
Conclusion
Sodium is an important element for the body. However, excess or too little sodium can be potentially hazardous. Before any corrective action, the cause of the sodium disorder should be known. The correction should rather be slow. Moreover, doctors should focus on early management as it brings out a positive outcome of the disease.
