Sodium is an essential electrolyte that is vital for maintaining fluid balance, nerve conduction, and normal cell function. However, low sodium levels, also known as hyponatremia, can be dangerous and even life-threatening if severe enough.
What are normal sodium levels?
Normal sodium levels in the blood are between 135-145 milliequivalents per liter (mEq/L). Levels below 135 mEq/L are considered hyponatremia or low sodium. The normal range may vary slightly between laboratories.
Normal sodium levels
| Sodium Level | Classification |
|---|---|
| 135-145 mEq/L | Normal |
What are the stages of hyponatremia?
Hyponatremia is classified into stages based on severity:
Stages of hyponatremia
| Sodium Level | Classification | Symptoms |
|---|---|---|
| 130-135 mEq/L | Mild hyponatremia | Usually asymptomatic |
| 125-130 mEq/L | Moderate hyponatremia | Nausea, headache, fatigue, muscle cramps |
| 120-125 mEq/L | Severe hyponatremia | Confusion, disorientation, seizures |
| Below 120 mEq/L | Profound hyponatremia | Coma, respiratory arrest, brain stem herniation |
As sodium levels drop lower, symptoms become more severe. Even mild chronic hyponatremia can impair cognition and increase fall risk in the elderly.
At what sodium level does death occur?
There is no definitive sodium level that causes death. However, profoundly low sodium levels below 120 mEq/L can be fatal. At these critically low levels, fluid shifts into the brain cells causing severe cerebral edema, brain stem compression, and herniation. This results in coma, respiratory arrest, and brain stem death.
Rapid over-correction of chronic hyponatremia can also lead to fatal osmotic demyelination syndrome. Therefore, sodium levels in chronic hyponatremia should be corrected slowly at no more than 10-12 mEq/L in 24 hours.
Potentially fatal sodium levels
| Sodium Level | Risk |
|---|---|
| Below 120 mEq/L | High risk of coma, respiratory arrest, brain stem herniation |
| Rapid rise in chronic hyponatremia | Risk of osmotic demyelination |
What causes low sodium levels?
There are many possible causes of hyponatremia including:
- Dehydration
- Over-hydration
- Congestive heart failure
- Liver failure
- Kidney disease
- Adrenal insufficiency
- Hypothyroidism
- Syndrome of inappropriate antidiuretic hormone (SIADH)
- Medications like diuretics, antidepressants, anti-seizure
- Low dietary solute intake
- Excessive water intake
- Gastroenteritis with vomiting and diarrhea
- Burns
- Traumatic brain injury
- Surgery
Identifying and promptly treating the underlying cause is key to reversing low sodium levels.
How is hyponatremia diagnosed?
The diagnosis of hyponatremia involves:
- Checking serum sodium level: This is the primary test to diagnose and classify hyponatremia based on severity.
- Assessing volume status: Determining if patient is hypovolemic, euvolemic or hypervolemic guides cause.
- Urinalysis: Urine osmolality and sodium help determine cause like SIADH or renal losses.
- Blood tests: Checking glucose, kidney function, thyroid, adrenal function.
- Imaging: CT, MRI to rule out adrenal or pituitary tumors, pulmonary disease.
- Medication review: Many drugs like diuretics and antidepressants cause hyponatremia.
How is hyponatremia treated?
Treatment of hyponatremia depends on the severity, cause and speed of onset. Key aspects include:
- Fluid restriction: Restricting fluid intake to less than urine output.
- Salt tablets: Increased salt and solute intake.
- Treating underlying causes: Correcting thyroid, adrenal, heart, liver and kidney disorders.
- Medication adjustment: Reducing or stopping diuretics, antidepressants, anti-seizures.
- Medications: Vasopressin receptor antagonists and demeclocycline reduce renal water reabsorption.
- Hypertonic saline: Used in severe acute hyponatremia with neurological symptoms to raise sodium levels by 1-2 mEq/L/hour.
- Careful monitoring: Frequent sodium checks, neurological status assessments and supportive care.
The primary goals are to treat the underlying disorder, reverse brain swelling in acute cases and gradually normalize sodium levels.
What are the complications of hyponatremia?
Complications of significant hyponatremia include:
- Cerebral edema: Swelling of brain cells causes headache, nausea, seizures, reduced consciousness and herniation.
- Osmotic demyelination syndrome: Damage to the myelin sheath around nerves when sodium correction is too rapid.
- Respiratory arrest: The drive to breathe is impaired leading to respiratory failure.
- Cardiac arrhythmias: Abnormal heart rhythms from electrolyte disturbances.
- Death: From brain herniation, respiratory arrest or arrhythmias in profound hyponatremia.
Can hyponatremia be fatal in the elderly?
Yes, even mildly low sodium levels increase mortality risk in the elderly. Reasons include:
- The elderly have less brain adaptability and are prone to cerebral edema with lower sodium drops than younger individuals.
- They have less thirst perception and are prone to over-hydration.
- Common conditions like heart, liver and kidney disease raise hyponatremia risk.
- Many take diuretics, SSRIs and other drugs causing sodium loss.
- Cognitive impairment impairs ability to get water balance right.
- Unsteady gait from low sodium increases falls and complications.
- Comorbidities like pneumonia or UTI in setting of hyponatremia have higher mortality.
Even mild chronic hyponatremia below 135 mEq/L can double the risk of falls and fractures. Prompt diagnosis and management of hyponatremia reduces mortality in elderly.
Are there ways to prevent hyponatremia?
Some ways to prevent hyponatremia include:
- Avoiding over-hydration during exercise events like marathons.
- Moderating fluid intake in the elderly and patients on fluid restricting diets.
- Regular blood electrolyte screening in high risk groups.
- Monitoring for drug interactions causing hyponatremia.
- Educating patients on medications like diuretics and SSRIs to watch for symptoms.
- Treating underlying medical conditions like adrenal, thyroid and hormonal disorders.
- Consuming adequate solutes like salt and protein.
Lifestyle modifications and prompt treatment of medical issues helps prevents severe sodium drops.
Conclusion
In summary, the severity of symptoms and mortality risk in hyponatremia correlate with the degree of sodium drop. While mild chronic hyponatremia may have subtle symptoms, profound levels below 120 mEq/L can lead to life-threatening complications like brain herniation and respiratory arrest. However, severe hyponatremia is preventable through appropriate fluid balance, regular monitoring, and prompt diagnosis and management of underlying medical conditions. This is especially important in vulnerable populations like the elderly.