What is the role of hypertonic saline in treating hyponatremia?

Role of Hypertonic Saline in Treating Hyponatremia

Hypertonic saline (3%) is strongly recommended for treating severe symptomatic hyponatremia with a targeted increase of 4-6 mEq/L within 1-2 hours, while ensuring that correction does not exceed 8-10 mEq/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2

Classification and Assessment of Hyponatremia

Before initiating treatment, proper assessment of hyponatremia is crucial:

1. Severity classification:

   • 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 assessment:

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

Indications for Hypertonic Saline

Hypertonic saline is primarily indicated for:

• Severe symptomatic hyponatremia (somnolence, obtundation, coma, seizures, or cardiorespiratory distress) 2
• Acute neurologic hyponatremia 3
• Threatened intracranial hypertension or signs of brain herniation 4

Administration Protocol

For Severe Symptomatic Hyponatremia:

1. Initial bolus:

   • 3% hypertonic saline to increase serum sodium by 4-6 mEq/L within 1-2 hours 1
   • Typically administered as 150 mL bolus of 3% hypertonic saline 5

2. Maintenance phase:

   • After initial correction, slow the rate to avoid osmotic demyelination syndrome
   • Maximum correction rate should not exceed 8 mmol/L in 24 hours 1
   • Avoid increasing serum sodium by >10 mmol/L/day 1, 2

3. Monitoring:

   • Check sodium levels every 2 hours initially, then every 4 hours during treatment 1
   • Monitor diuresis as it correlates with the degree of sodium overcorrection 5

For Traumatic Brain Injury:

• Administer mannitol 20% or hypertonic saline at a dose of 250 mOsm, in infusion over 15–20 minutes 4

Safety Considerations and Pitfalls

1. Risk of overcorrection:

   • Overcorrection occurs more frequently in severely symptomatic patients (38% vs 6% in moderate symptoms) 5
   • Patients with initial sodium <105 mEq/L should have sodium raised by only 20 mEq/L initially 6

2. Osmotic demyelination syndrome (ODS):

   • Can result from overly rapid correction of chronic hyponatremia
   • Can lead to parkinsonism, quadriparesis, or death 2
   • Risk is higher when correcting chronic hyponatremia (>48 hours) 1

3. Special populations:

   • In cirrhotic patients: consider volume expansion with colloid or saline for serum sodium <120 mmol/L 1
   • Avoid 4% albumin solution in severe traumatic brain injury patients 4

Efficacy and Outcomes

• A standardized sliding-scale hypertonic saline protocol has shown that 84.3% of treatment time can be spent in goal sodium range (136-145 mEq/L) 3
• Hypertonic saline provides more constant sodium increase compared to conventional therapies 5
• Conventional therapies carry a higher risk for insufficient sodium correction at 24 hours compared to hypertonic saline (RR: 2.8,95% CI: 1.4-5.5) 5

Alternative Treatments

For less severe cases or specific etiologies:

• Fluid restriction (1-1.5 L/day) as first-line treatment for mild to moderate hyponatremia 1
• Tolvaptan (vasopressin receptor antagonist) for short-term treatment (≤30 days) of hyponatremia 1
• Treatment of underlying causes (optimizing heart failure medications, thyroid hormone replacement) 1

Hypertonic saline remains the cornerstone of treatment for severe symptomatic hyponatremia, with careful attention to correction rates and monitoring to maximize efficacy while minimizing the risk of complications.