What fluid is most appropriate for a patient with severe hypernatremia (serum sodium ≈ 168 mEq/L)?

Fluid Management for Severe Hypernatremia (Sodium 168 mEq/L)

For a patient with severe hypernatremia at 168 mEq/L, hypotonic fluids—specifically 5% dextrose in water (D5W)—are the initial fluid of choice, as they provide free water without adding sodium load. 1

Initial Fluid Selection

• D5W (5% dextrose in water) is the preferred first-line fluid because it delivers no renal osmotic load and allows controlled, gradual decrease in plasma osmolality 1
• Isotonic saline (0.9% NaCl) must be avoided as initial therapy because it delivers excessive osmotic load—requiring 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid—which risks worsening hypernatremia 1
• Alternative hypotonic options include 0.45% saline (half-normal saline) if D5W is not available, though D5W remains superior for severe hypernatremia 1, 2

Critical Correction Rate Guidelines

• The maximum safe correction rate is 8-10 mmol/L per 24 hours for chronic hypernatremia (>48 hours duration) to prevent cerebral edema 1, 3
• Correction should be paced over 48-72 hours to replace the calculated water deficit safely 4
• Too rapid correction can precipitate cerebral edema and worsen neurological status, potentially leading to seizures or coma 4, 3

Initial Fluid Administration Rate

• For adults: calculate 25-30 mL/kg/24 hours as the baseline physiological maintenance requirement 1
• Adjust the infusion rate so that serum sodium decreases no faster than 0.4 mmol/L per hour (approximately 10 mmol/L per day maximum) 1
• Monitor serum sodium every 2-4 hours during the initial correction phase to ensure safe correction velocity 1

Volume Status Assessment

• Assess whether the patient is hypovolemic, euvolemic, or hypervolemic before initiating treatment, as this guides additional interventions 1
• In hypernatremic dehydration, intravascular volume is usually preserved, so isotonic crystalloids are rarely needed except in true hypovolemic shock 1
• If signs of severe hypovolemia exist (hypotension, tachycardia, poor perfusion), a small bolus of isotonic saline may be given first to restore hemodynamic stability, followed immediately by transition to hypotonic fluids 2

Special Considerations

• Patients with nephrogenic diabetes insipidus (NDI) are particularly prone to hypernatremic dehydration and require prompt IV rehydration with hypotonic fluids 1
• In NDI patients, D5W is especially preferred because their dilute urine (very low sodium concentration) aligns with the low-sodium composition of D5W 1
• Avoid bolus administration of D5W, as rapid infusion can precipitate a swift fall in serum sodium and increase cerebral edema risk; instead, use continuous controlled infusion 1

Monitoring Protocol

• Place a urinary catheter to allow accurate measurement of urine output during D5W therapy 1
• Check serum sodium every 2-4 hours initially, then every 4-6 hours once correction is proceeding safely 1
• Assess volume status, urinary output, and clinical response continuously during treatment 1
• Watch for neurological deterioration (confusion, seizures, altered consciousness) which may indicate either inadequate correction or overly rapid correction 2, 3

Common Pitfalls to Avoid

• Never use isotonic saline as primary therapy for hypernatremia—this adds more sodium load and can worsen the condition 1
• Never correct chronic hypernatremia faster than 8-10 mmol/L per day—rapid correction causes cerebral edema 1, 3
• Never give D5W as a rapid bolus—this can precipitate dangerous rapid sodium decline 1
• Never delay treatment while pursuing extensive diagnostic workup; begin hypotonic fluid replacement promptly once hypernatremia is confirmed 2