What is the management of hyponatremia according to Australian guidelines?

Management of Hyponatremia According to Australian Guidelines

The management of hyponatremia should be guided by the patient's volume status (hypovolemic, euvolemic, or hypervolemic), severity of symptoms, and underlying cause, with correction rates not exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Classification and Assessment

Hyponatremia should be classified by:

1. Severity:

   • Mild: 126-135 mEq/L (often asymptomatic)
   • Moderate: 120-125 mEq/L (nausea, headache, confusion)
   • Severe: <120 mEq/L (risk of seizures, coma, respiratory arrest) 1

2. Volume status:

   • Hypovolemic: Orthostatic hypotension, dry mucous membranes, tachycardia; urine sodium <20 mEq/L
   • Euvolemic: No edema, normal vital signs; urine sodium >20-40 mEq/L
   • Hypervolemic: Edema, ascites, elevated JVP; urine sodium <20 mEq/L 1

Management Based on Volume Status

Hypervolemic Hyponatremia

• Primary approach: Treat the underlying cause (heart failure, cirrhosis, renal failure) 1
• Fluid restriction: 1-1.5 L/day for severe hyponatremia (serum sodium <125 mmol/L) 1
• Salt restriction: Moderate salt restriction with daily intake of 5-6.5 g (87-113 mmol sodium) 1
• Diuretic therapy:
  • For ascites: Start spironolactone 100 mg/day, increasing to maximum 400 mg/day if needed 1
  • For recurrent severe ascites: Combination therapy with spironolactone (100-400 mg) and furosemide (40-160 mg) 1
  • Caution: Temporarily discontinue diuretics if sodium <125 mmol/L, worsening renal function, or hepatic encephalopathy occurs 1

Euvolemic Hyponatremia (often SIADH)

• Fluid restriction: 500 ml/day initially, adjusted according to serum sodium levels 2
• Pharmacological options:
  • Tolvaptan: For short-term treatment (≤30 days), starting dose 15 mg once daily 1
  • Urea: Effective and safe alternative for SIADH 2

Hypovolemic Hyponatremia

• Volume replacement: Normal saline infusions to restore intravascular volume 3
• Address underlying cause: GI losses, diuretics, cerebral salt wasting, adrenal insufficiency 1

Management of Severe Symptomatic Hyponatremia

For patients with severe symptoms (somnolence, seizures, coma):

• Hypertonic saline (3%): Administer to increase serum sodium by 4-6 mEq/L within 1-2 hours 1
• Administration method: 100-150 ml intravenous bolus or continuous infusion 2
• Monitoring: Check sodium levels every 2 hours initially, then every 4 hours during treatment 1
• For intracranial hypertension: Mannitol 20% or hypertonic saline at 250 mOsm, infused over 15-20 minutes 1

Critical Safety Considerations

• Maximum correction rate: Do not exceed 8 mmol/L in 24 hours 1
• Avoid increasing serum sodium by >10 mmol/L/day to prevent osmotic demyelination syndrome 1
• Risk of overcorrection: Present in 4.5% to 28% of treated patients; requires vigilant monitoring 4
• For overcorrection: Be prepared to administer hypotonic fluids or desmopressin 2

Special Populations

1. Cirrhotic patients:

   • Avoid water restriction in uncomplicated ascites
   • Stop diuretics and observe for serum sodium 121-125 mmol/L
   • Consider volume expansion with colloid or saline for serum sodium <120 mmol/L 1

2. Heart failure patients:

   • Optimize heart failure medications (ACE inhibitors, beta-blockers, mineralocorticoid receptor antagonists) 1
   • Diuretics should not be used in isolation but combined with other guideline-directed medical therapy 1

3. Hypothyroidism-induced hyponatremia:

   • Primary treatment with thyroid hormone replacement therapy 1

Complications and Prognosis

• Untreated severe hyponatremia: Can lead to seizures, coma, and death, especially with sodium <120 mEq/L 1
• Mortality risk: 25% in patients with sodium <120 mEq/L vs 9.3% in patients with sodium >120 mEq/L 1
• Chronic mild hyponatremia: Associated with cognitive impairment, gait disturbances, falls, and fractures 4
• Osmotic demyelination: Rare but severe neurological complication of overly rapid correction 4

Common Pitfalls to Avoid

• Treating laboratory values without clinical context: Always assess volume status and symptoms
• Overly rapid correction: Can lead to irreversible neurological damage
• Inadequate monitoring: Sodium levels must be checked frequently during correction
• Failure to identify and treat underlying cause: Essential for successful management
• Inappropriate fluid restriction: May be ineffective in approximately half of SIADH patients 2