What are the symptoms and treatment of hyponatremia?

Symptoms and Treatment of Hyponatremia

Hyponatremia (serum sodium <135 mEq/L) is the most common electrolyte abnormality in hospitalized patients, affecting approximately 15-30% of children and adults, and requires treatment based on severity, chronicity, and underlying cause to prevent serious neurological complications. 1

Symptoms of Hyponatremia

Symptoms vary based on severity and onset speed:

Mild Hyponatremia (126-135 mEq/L)

• Often asymptomatic or nonspecific
• Weakness
• Headache
• Nausea
• Confusion
• Muscle cramps
• Fussiness (in children)
• Cognitive impairment
• Gait disturbances
• Increased risk of falls 1, 2

Moderate Hyponatremia (120-125 mEq/L)

• All mild symptoms plus:
• Vomiting
• Lethargy
• Confusion
• More pronounced headache
• Disorientation 1

Severe Hyponatremia (<120 mEq/L)

• Life-threatening manifestations:
• Seizures
• Coma
• Respiratory arrest
• Brain herniation (rare)
• Death 1

Important Clinical Consideration

• Acute hyponatremia (<48 hours) typically causes more severe symptoms than chronic hyponatremia (>48 hours) at the same sodium level
• Children are at higher risk for symptomatic hyponatremia due to their larger brain/skull size ratio 1

Diagnostic Approach

First, determine volume status to classify the type of hyponatremia:

1. Hypovolemic hyponatremia

   • Causes: Poor oral intake, diuretic excess, gastrointestinal losses
   • Signs: Dry mucous membranes, decreased skin turgor, orthostatic hypotension
   • Lab: Urine sodium <20 mEq/L (unless renal losses)

2. Euvolemic hyponatremia

   • Causes: SIADH, medications (SSRIs, carbamazepine), hypothyroidism, adrenal insufficiency
   • Signs: No edema, no signs of volume depletion
   • Lab: Urine sodium >20 mEq/L, urine osmolality >500 mOsm/kg

3. Hypervolemic hyponatremia

   • Causes: Heart failure, cirrhosis, renal disease
   • Signs: Edema, ascites
   • Lab: Varies based on underlying condition 1, 2

Treatment of Hyponatremia

Emergency Treatment for Severe Symptomatic Hyponatremia

• For patients with seizures, coma, or respiratory distress:
• Administer 3% hypertonic saline IV to increase serum sodium by 4-6 mEq/L within 1-2 hours
• Do not exceed correction of 10 mEq/L in first 24 hours to avoid osmotic demyelination syndrome 1, 2

Treatment Based on Volume Status

1. Hypovolemic Hyponatremia

• Discontinue diuretics if applicable
• Isotonic (0.9%) saline infusion
• Treat underlying cause (e.g., diarrhea, vomiting) 1, 3

2. Euvolemic Hyponatremia (including SIADH)

• Mild (126-135 mEq/L): Fluid restriction alone (monitor)
• Moderate (120-125 mEq/L): Fluid restriction to 1,000 mL/day
• Severe (<120 mEq/L): More severe fluid restriction plus albumin infusion
• For persistent cases: Consider vasopressin receptor antagonists (vaptans) or demeclocycline 1, 4

3. Hypervolemic Hyponatremia

• Fluid restriction
• Treat underlying cause (heart failure, cirrhosis)
• Loop diuretics with careful monitoring
• Salt restriction
• In severe cases: Albumin infusion or vasopressin receptor antagonists 1, 3

Special Considerations

1. Rate of Correction

   • Acute hyponatremia (<48 hours): Can correct more rapidly
   • Chronic hyponatremia (>48 hours): Correct slowly to avoid osmotic demyelination syndrome
   • High-risk patients (alcoholism, malnutrition, liver disease): Use even slower correction rates 4, 2

2. Tolvaptan Use

   • FDA-approved for euvolemic and hypervolemic hyponatremia
   • Must be initiated in hospital setting with close monitoring
   • Starting dose: 15 mg once daily, can be titrated up to 60 mg
   • Not for use in patients who need urgent sodium correction
   • Limited to 30 days to minimize liver injury risk 4

3. Monitoring

   • Check serum sodium every 4-6 hours during active correction
   • If correction exceeds 10 mEq/L/24 hours, consider administering hypotonic fluids or desmopressin to re-lower sodium 4, 2

Pitfalls to Avoid

1. Overly rapid correction of chronic hyponatremia leading to osmotic demyelination syndrome
2. Inadequate monitoring during treatment
3. Failure to identify and treat the underlying cause
4. Inappropriate fluid therapy (e.g., hypotonic fluids in SIADH)
5. Delayed treatment of severe symptomatic hyponatremia, which can lead to permanent neurological damage 1, 4, 2

Remember that hyponatremia is often a marker of underlying disease severity, and addressing the primary condition is essential for successful management.