What are the symptoms, workup, and treatment of hyponatremia (low sodium levels) due to water intoxication?

Water Intoxication: Symptoms, Workup, and Treatment

Water intoxication causes hyponatremia through excessive free water intake, leading to potentially life-threatening complications. The first step in treating water intoxication is to determine the type of hyponatremia (hypovolemic, euvolemic, or hypervolemic) and treat according to symptom severity, with fluid restriction being the primary intervention for most cases of water intoxication. 1

Symptoms

Symptoms vary based on severity and rapidity of onset:

Mild to Moderate Symptoms (Na 125-134 mEq/L)

• Nausea and vomiting
• Headache
• Weakness
• Mild neurocognitive deficits
• Gait disturbances
• Increased fall risk 2

Severe Symptoms (Na <125 mEq/L)

• Delirium and confusion
• Impaired consciousness
• Ataxia
• Seizures
• Coma
• Brain herniation (rare)
• Death 3

Chronic hyponatremia is associated with:

• Cognitive impairment
• Increased fracture risk (23.3% vs 17.3% in normonatremic patients)
• Secondary osteoporosis 2

Diagnostic Workup

Initial Assessment

1. Serum sodium measurement - defines hyponatremia (<135 mEq/L)

   • Mild: 130-134 mEq/L
   • Moderate: 125-129 mEq/L
   • Severe: <125 mEq/L 3

2. Volume status assessment

   • Note: Physical examination alone has poor sensitivity (41.1%) for determining extracellular fluid status 1
   • Additional assessment methods include:
     • Central venous pressure measurements
     • Daily weight measurements
     • Fluid intake/output monitoring 1

3. Laboratory tests

   • Serum osmolality (to confirm hypotonic hyponatremia)
   • Urine osmolality
   • Urine sodium concentration
   • Serum uric acid (<4 mg/dL suggests SIADH) 1
   • Spot urine Na/K ratio (>1 represents sodium excretion >78 mmol/day) 1

Diagnostic Algorithm

1. Confirm hypotonic hyponatremia (serum osmolality <275 mOsm/kg)
2. Determine volume status:
   • Hypovolemic: signs of dehydration, orthostatic hypotension
   • Euvolemic: normal volume status (most common in water intoxication)
   • Hypervolemic: edema, ascites 1, 3
3. Assess urine sodium:
   • <30 mmol/L in hypovolemic states

   • 30 mmol/L in SIADH 1

Treatment

Treatment depends on:

1. Severity of symptoms
2. Duration of hyponatremia
3. Volume status

Emergency Treatment for Severe Symptomatic Hyponatremia

For patients with seizures, coma, or severe neurological symptoms:

• Administer 3% hypertonic saline as bolus infusion
• Goal: Increase serum sodium by 4-6 mEq/L within 1-2 hours
• Critical safety principle: Do not correct serum sodium by more than 8-10 mEq/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Monitor serum sodium every 2 hours initially 1

Treatment Based on Volume Status

Euvolemic Hyponatremia (Most Common in Water Intoxication)

1. First-line: Fluid restriction (1-1.5 L/day) 4, 1
2. Second-line options:
   • Ensure adequate solute intake
   • Consider vasopressin receptor antagonists (vaptans) for severe cases 1
   • Tolvaptan may be considered for euvolemic hyponatremia, but should be initiated in hospital setting 1, 5

Hypovolemic Hyponatremia

1. Fluid resuscitation with isotonic saline
2. Discontinue diuretics if applicable 1

Hypervolemic Hyponatremia

1. Fluid and sodium restriction
2. Treat underlying condition (heart failure, cirrhosis)
3. Consider albumin infusion in appropriate cases 1

Monitoring and Adjustment

• Monitor serum sodium:
  • Every 2 hours for severe symptoms
  • Every 4 hours for mild symptoms
  • Daily for asymptomatic patients 1
• Track fluid intake/output and daily weight
• Adjust treatment to prevent correction exceeding 8 mEq/L in 24 hours 1

Special Considerations

• Risk of osmotic demyelination syndrome: Higher in patients with advanced liver disease, alcoholism, malnutrition, and severe hyponatremia 1
• Vaptans: Tolvaptan has shown efficacy in clinical trials, improving serum sodium concentration in 45-82% of cases with euvolemic or hypervolemic hyponatremia 1, 5
• Adverse effects of vaptans: Include thirst (12% vs 2% placebo), dry mouth (7% vs 2%), and polyuria (4% vs 1%) 5
• Contraindications for vaptans: Hypovolemic hyponatremia, need for urgent sodium correction 5

Prevention of Recurrence

• Identify and address underlying causes
• Patient education about appropriate fluid intake
• Regular monitoring of serum sodium in high-risk patients
• Consider behavioral approaches to limit polydipsia in psychiatric patients 6