What are the symptoms and treatment of hyponatremia (low sodium levels)?

Symptoms and Treatment of Hyponatremia

Hyponatremia is characterized by nonspecific symptoms that can range from mild to severe and life-threatening, with treatment approaches based on symptom severity, acuity of onset, and underlying cause. 1, 2

Symptoms of Hyponatremia

Mild to Moderate Hyponatremia (Serum Sodium 125-134 mEq/L)

• Headache
• Nausea and vomiting
• Confusion
• Lethargy
• Muscle cramps
• Weakness
• Fussiness (in children)
• Cognitive impairment
• Gait disturbances
• Increased risk of falls and fractures 1, 3

Severe Hyponatremia (Serum Sodium <125 mEq/L)

• Delirium
• Impaired consciousness
• Ataxia
• Seizures
• Coma
• Brain herniation (rare)
• Death 1, 4

Important: Symptoms depend on both the absolute sodium level and the rate of development. Acute hyponatremia (developing in <48 hours) is more likely to cause severe neurological symptoms due to cerebral edema, while chronic hyponatremia may present with milder symptoms despite very low sodium levels. 1

Classification of Hyponatremia by Volume Status

1. Hypovolemic Hyponatremia

• Causes: Diuretic use (especially thiazides), gastrointestinal losses (vomiting, diarrhea), third-space losses, adrenal insufficiency
• Clinical signs: Dry mucous membranes, decreased skin turgor, orthostatic hypotension, tachycardia
• Laboratory: Urine sodium <20 mEq/L (except with diuretic use or adrenal insufficiency) 4, 5

2. Euvolemic Hyponatremia

• Causes: SIADH (Syndrome of Inappropriate Antidiuretic Hormone), medications, pain, nausea, stress, pulmonary disorders, CNS disorders
• Clinical signs: No edema or signs of volume depletion
• Laboratory: Urine sodium typically >20 mEq/L, urine osmolality inappropriately high (>500 mOsm/kg) 1

3. Hypervolemic Hyponatremia

• Causes: Heart failure, liver cirrhosis, nephrotic syndrome, renal failure
• Clinical signs: Edema, ascites, distended jugular veins, pulmonary rales
• Laboratory: Urine sodium typically <20 mEq/L (except in renal failure) 6

Treatment Approaches

Emergency Treatment for Severe Symptomatic Hyponatremia

• For seizures, coma, or severe neurological symptoms:
  • Administer 3% hypertonic saline as bolus doses
  • Aim to increase serum sodium by 4-6 mEq/L within 1-2 hours to reverse severe symptoms
  • Critical safety limit: Do not exceed correction of 8-10 mEq/L in 24 hours to avoid osmotic demyelination syndrome 2, 3
  • Monitor serum sodium every 2-4 hours initially 2

Treatment Based on Volume Status

1. Hypovolemic Hyponatremia

• Isotonic (0.9%) saline infusion to restore volume status
• Treat underlying cause (stop offending diuretics, replace gastrointestinal losses)
• Monitor serum sodium closely during rehydration 2, 4

2. Euvolemic Hyponatremia

• Fluid restriction (1-1.5 L/day) is first-line treatment
• For SIADH:
  • Salt tablets may be added if fluid restriction alone is insufficient
  • Tolvaptan (vasopressin V2 receptor antagonist) can be considered for short-term use (≤30 days):
    • Initial dose: 15 mg once daily
    • May increase to 30 mg once daily after 24 hours, maximum 60 mg daily
    • Must be initiated in hospital setting with close monitoring
    • Avoid fluid restriction during first 24 hours of therapy 2, 7
  • Demeclocycline for persistent cases 5

3. Hypervolemic Hyponatremia

• Fluid restriction (<1-1.5 L/day)
• Diuretic therapy (loop diuretics)
• Treat underlying condition (heart failure, cirrhosis)
• Salt restriction (≤6 g/day) 2, 6

Important Precautions

1. Avoid overly rapid correction of chronic hyponatremia (>8-10 mEq/L in 24 hours) to prevent osmotic demyelination syndrome, which can cause:

   • Dysarthria
   • Mutism
   • Dysphagia
   • Spastic quadriparesis
   • Seizures
   • Coma
   • Death 7

2. Higher risk patients for osmotic demyelination:

   • Severe malnutrition
   • Alcoholism
   • Advanced liver disease
   • Children (due to larger brain/skull size ratio) 1, 7

3. Monitor closely:

   • Serum sodium levels every 2-4 hours in symptomatic patients
   • Fluid input/output
   • Daily weight 2

Special Considerations

• Exercise-associated hyponatremia requires different management:

  • Education about proper hydration during exercise
  • Avoid excessive fluid intake during endurance events
  • Monitor weight before and after exercise 1

• Children are at particularly high risk of developing symptomatic hyponatremia because of their larger brain/skull size ratio 1

• Chronic mild hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures even when asymptomatic 3