What are the diagnosis and management of hyponatremia?

Diagnosis and Management of Hyponatremia

The management of hyponatremia must be based on the patient's volume status, severity of symptoms, and chronicity of the condition, with treatment tailored to the underlying etiology while carefully monitoring correction rates to prevent neurological complications.

Diagnostic Approach

Classification by Volume Status

• Hypovolemic: Decreased extracellular fluid volume
• Euvolemic: Normal extracellular fluid volume
• Hypervolemic: Increased extracellular fluid volume

Essential Laboratory Tests

• Serum sodium and osmolality
• Urine osmolality and sodium concentration
• Thyroid function tests and cortisol levels
• Fractional excretion of urate (improves diagnostic accuracy for SIADH to 95%) 1

Diagnostic Algorithm

Volume Status	Urine Osmolality	Urine Sodium	Likely Diagnosis
Hypovolemic	Variable	<20 mEq/L	Volume depletion, GI losses
Hypovolemic	Variable	>20 mEq/L	Diuretic use, renal salt wasting
Euvolemic	>500 mOsm/kg	>20-40 mEq/L	SIADH
Hypervolemic	Elevated	<20 mEq/L	Heart failure, cirrhosis

SIADH Diagnostic Criteria 2, 1

• Hyponatremia (serum sodium <134 mEq/L)
• Hypoosmolality (plasma osmolality <275 mOsm/kg)
• Inappropriately high urine osmolality (>500 mOsm/kg)
• Inappropriately high urinary sodium concentration (>20 mEq/L)
• Absence of hypothyroidism, adrenal insufficiency, or volume depletion

Management Based on Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Respiratory Distress)

• Immediate treatment with 3% hypertonic saline as 100-150 mL bolus or continuous infusion 1
• Target correction: 4-6 mEq/L in first 6 hours or until symptoms improve
• Maximum correction: 8 mEq/L in 24 hours, not exceeding 12 mEq/L in 48 hours 1, 3
• Monitor serum sodium every 2-4 hours during active correction 1

Moderate Hyponatremia (120-125 mEq/L)

• Fluid restriction to 1,000 mL/day 2
• Treat underlying cause
• Consider oral sodium chloride tablets if no response to fluid restriction 1

Mild Hyponatremia (126-135 mEq/L)

• Often requires only monitoring and mild fluid restriction 2
• Address underlying cause

Management Based on Volume Status

Hypovolemic Hyponatremia

• Isotonic (0.9%) saline infusion for plasma volume expansion 1
• Discontinue diuretics or other causative medications
• Reassess sodium levels after volume status correction

Euvolemic Hyponatremia (SIADH)

• Fluid restriction (1-1.5 L/day) and high solute intake (salt and protein) 1
• For refractory cases:
  • Tolvaptan (vasopressin receptor antagonist) starting at 15 mg once daily, can be titrated up to 60 mg daily 4
  • Urea (30-60 g/day) can be considered as an alternative 1
  • Demeclocycline may be used 2

Hypervolemic Hyponatremia

• Fluid restriction to 1,000 mL/day for moderate hyponatremia 2
• More severe fluid restriction with albumin infusion for severe hyponatremia 2
• Loop diuretics for volume management 1
• Treatment of underlying condition (heart failure, cirrhosis)

Special Considerations

Correction Rate and Monitoring

• Maximum correction rate for chronic hyponatremia: 8 mEq/L in 24 hours 1
• High-risk patients (alcoholism, malnutrition, liver disease): lower correction rate of 4-6 mEq/L per day 1
• If overcorrection occurs, administer hypotonic fluids or desmopressin to prevent osmotic demyelination syndrome (ODS) 1

Complications and Prevention

• Early detection prevents severe hyponatremia leading to seizures, coma, and death 2
• Even mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 3
• Risk factors for ODS: chronic hyponatremia, alcoholism, liver disease, malnutrition, and hypokalemia 1

Medication Considerations

• Discontinue medications that may cause or worsen hyponatremia (SSRIs, carbamazepine, thiazide diuretics, NSAIDs) 1
• Tolvaptan can cause gastrointestinal bleeding in patients with cirrhosis (10% vs 2% with placebo) 4
• Monitor for hypernatremia during tolvaptan treatment 4

Specific Clinical Scenarios

Hyponatremia in Cirrhosis

• Mild hyponatremia: fluid restriction to 1,000 mL/day 2
• Severe hyponatremia: more severe fluid restriction with albumin infusion 2
• Avoid vaptans in patients with liver disease due to risk of gastrointestinal bleeding 4

Hyponatremia in Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting 2
• Cerebral salt wasting: treat with replacement of serum sodium and intravenous fluids 2
• Avoid fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 2

By following this structured approach to diagnosis and management, clinicians can effectively treat hyponatremia while minimizing the risk of complications from both the condition itself and its treatment.