What is the initial infusion rate of 3% Sodium Chloride (NaCl) for a patient with severe hyponatremia?

Initial Infusion Rate of 3% Sodium Chloride for Severe Hyponatremia

For patients with severe symptomatic hyponatremia, 3% NaCl should be administered at a rate calculated to increase serum sodium by 1-2 mmol/L per hour until symptoms abate, with a total correction not exceeding 8 mmol/L in 24 hours. 1, 2

Calculation of Initial Rate

The initial infusion rate can be determined using the following formula:

• Initial rate (ml/kg/hour) = Body weight (kg) × desired rate of increase in sodium (mmol/L per hour) 1

For example:

• For a 70 kg patient requiring a 1 mmol/L per hour increase: 70 ml/hour
• For a 70 kg patient requiring a 2 mmol/L per hour increase: 140 ml/hour

Treatment Algorithm Based on Symptom Severity

For Severe Symptoms (seizures, coma, altered mental status)

• Start 3% NaCl at calculated rate to increase sodium by 1-2 mmol/L per hour
• Target correction of 6 mmol/L over first 6 hours or until severe symptoms resolve 2
• Check serum sodium every 2 hours 3
• Once severe symptoms resolve, recalculate 3% NaCl requirement or switch to protocol for mild symptoms 2
• Do not exceed total correction of 8 mmol/L in 24 hours 2, 3

For Mild Symptoms (nausea, vomiting, headache)

• Consider fluid restriction (1L/day) if euvolemic 2
• Monitor serum sodium every 4 hours 3
• If sodium <120 mmol/L, consider 3% NaCl at lower rate

Important Safety Considerations

• Risk of Osmotic Demyelination Syndrome: Overly rapid correction (>8-10 mmol/L in 24 hours) can lead to permanent neurological damage 3, 4

• Monitoring Requirements:

  • Check serum sodium every 2 hours in severely symptomatic patients 3
  • Monitor urine output and specific gravity every 4 hours to detect water diuresis 3
  • Track fluid intake/output and daily weight 3

• Risk Factors for Overcorrection:

  • Severe symptoms (38% vs 6% overcorrection rate compared to moderate symptoms) 3
  • High urine output or sudden decrease in urine specific gravity ≥0.010 3
  • Hypovolemia misinterpreted as symptomatic hyponatremia 3

Special Considerations

• Chronic vs. Acute Hyponatremia: Rapid correction is more appropriate for acute hyponatremia (developed within 48 hours) 2

• Neurosurgical Patients: Avoid fluid restriction in patients with subarachnoid hemorrhage at risk of vasospasm 3

• Sodium Deficit Calculation: For precise dosing, sodium deficit can be calculated using: Na deficit = Desired increase in Na (mEq) × (0.5 × ideal body weight) 2

• Treatment Adjustment: If sodium correction exceeds target rate, consider administering D5W to slow correction 5

By following this algorithm and carefully monitoring serum sodium levels, the risk of complications can be minimized while effectively treating the potentially life-threatening condition of severe hyponatremia.