What is the appropriate D5W (5% Dextrose in Water) infusion rate for a patient with hypernatremia and a body weight of 47kg?

Hypernatremia Treatment with D5W: Infusion Rate Calculation

Direct Answer

For a 47 kg patient with serum sodium of 164 mEq/L, initiate D5W at approximately 50-75 mL/hour, targeting correction of no more than 8-10 mEq/L per 24 hours to avoid cerebral edema. 1, 2

Calculation Framework

Step 1: Calculate Water Deficit

• Water deficit = 0.6 × body weight (kg) × [(current Na ÷ 140) - 1]
• For this patient: 0.6 × 47 × [(164 ÷ 140) - 1] = 4.8 liters deficit 1

Step 2: Determine Safe Correction Rate

• Maximum safe correction: 8-10 mEq/L per 24 hours to prevent osmotic demyelination 1, 2
• Too rapid correction can cause fatal cerebral edema, as demonstrated in cases where aggressive correction led to fatal arrhythmias 2
• The water deficit should be replaced over 48-72 hours, not acutely 1

Step 3: Calculate Hourly Infusion Rate

• Total deficit (4.8 L) ÷ 48-72 hours = 67-100 mL/hour range
• Start conservatively at 50-75 mL/hour for the first 24 hours 1
• This rate provides approximately 2.5-3.75 grams dextrose/hour, well below the maximum 0.5 g/kg/hour (23.5 g/hour for 47 kg) that prevents glycosuria 3

Critical Monitoring Requirements

Immediate Laboratory Monitoring

• Check serum sodium every 2-4 hours initially to ensure correction rate stays within safe limits 1, 2
• If sodium drops >10 mEq/L in first 24 hours, reduce infusion rate by 50% 1
• Monitor for signs of cerebral edema: altered mental status, seizures, worsening neurological exam 2

Ongoing Assessment

• Measure urine output hourly - polyuria suggests possible diabetes insipidus requiring additional workup 4
• Check blood glucose every 4-6 hours to avoid hyperglycemia from dextrose infusion 3
• Assess volume status: if hypervolemic hypernatremia, add furosemide 20-40 mg IV to achieve negative fluid balance while correcting sodium 5

Common Pitfalls to Avoid

Overcorrection Risk

• Never exceed 10 mEq/L correction in 24 hours - extreme hypernatremia cases have resulted in fatal ventricular arrhythmias from QT prolongation when corrected too rapidly 2
• In one reported case, a patient with sodium 226 mEq/L developed fatal ventricular tachycardia despite "appropriate" correction to 160 mEq/L over 24 hours 2

Volume Status Mismanagement

• If patient is hypervolemic (volume overloaded), D5W alone will worsen fluid overload 5
• Add loop diuretic to create negative fluid balance exceeding negative sodium balance in hypervolemic cases 5
• For cardiac or renal compromise, limit D5W to ≤100 mL/hour and monitor closely for pulmonary edema 6

Underlying Cause Identification

• Hypernatremia refractory to D5W suggests diabetes insipidus - check urine osmolality and consider desmopressin 4
• Low urine output with hypernatremia may indicate hypothyroidism causing renal dysfunction 4

Adjusted Algorithm for This Patient

Initial 24 hours:

• Start D5W at 60 mL/hour (conservative mid-range)
• Check sodium at 4,8,12,24 hours
• Target sodium reduction to 154-156 mEq/L by 24 hours

Hours 24-48:

• If sodium appropriately decreased 8-10 mEq/L, continue at 60-75 mL/hour
• If sodium decreased <6 mEq/L, increase to 100 mL/hour
• If sodium decreased >12 mEq/L, reduce to 30-40 mL/hour

Hours 48-72:

• Adjust rate to complete correction of remaining deficit
• Transition to oral free water intake as patient tolerates