How to manage hypernatremia in the Intensive Care Unit (ICU)?

Management of Hypernatremia in the ICU

Correct hypernatremia in critically ill patients using electrolyte-free water at a rate not exceeding 8-10 mmol/L per 24 hours (≤0.5 mmol/L/hour), as allowing hypernatremia to persist is associated with increased mortality and length of stay. 1, 2

Initial Assessment

Immediately evaluate the following to determine the mechanism:

• Volume status: Check for signs of hypovolemia (hypotension, tachycardia, dry mucous membranes) versus hypervolemia (edema, jugular venous distention) 1
• Urine electrolytes and osmolality: Distinguish between renal water losses (urine osmolality <300 mOsm/kg suggests diabetes insipidus) versus extrarenal losses 1, 3
• Medication review: Identify sodium-containing fluids, mannitol, sodium bicarbonate, or diuretics that may contribute 4
• Fluid balance: Determine if hypernatremia developed with negative fluid balance (inadequate water) or positive fluid balance (excessive sodium administration) 4

Treatment Strategy

Fluid Selection and Administration

• First-line therapy: Administer electrolyte-free water (D5W or enteral water) to replace the calculated free water deficit 1, 3
• Alternative option: Use hypotonic saline (0.45% NaCl) if some sodium replacement is needed, but avoid isotonic fluids which worsen hypernatremia in patients with renal concentrating defects 1
• Calculate free water deficit: Use the formula: Free water deficit (L) = 0.5 × body weight (kg) × [(current Na/140) - 1], then add ongoing losses 1

Correction Rate Guidelines

Maximum correction rate: 8-10 mmol/L per 24 hours or ≤0.5 mmol/L per hour 5, 1

• This rate prevents cerebral edema, seizures, and neurological injury from rapid osmotic water shift into brain cells 5, 1
• The induced change in serum osmolality should not exceed 3 mOsm/kg H₂O per hour 6
• For chronic hypernatremia (>48 hours duration), correction should generally not exceed 8-10 mmol/L per 24 hours 5

Important caveat: Recent research suggests that rapid correction (>0.5 mmol/L/hour) was not associated with increased mortality, seizures, or cerebral edema in critically ill adults 7. However, guideline recommendations remain conservative at ≤0.5 mmol/L/hour until further evidence emerges 5, 1.

Monitoring Protocol

• Initial phase: Measure serum sodium every 2-4 hours until stable 1
• Stabilization phase: Measure every 6-8 hours once correction rate is appropriate 1
• Adjust therapy: Slow free water administration or add sodium-containing fluids if sodium is correcting too rapidly (>0.5 mmol/L/hour) 1
• Track: Urine output, urine electrolytes, and fluid balance to guide ongoing management 1, 3

Special Considerations in ICU Patients

Common Mechanisms in Critical Illness

• Polyuria with inadequate water replacement: ICU patients average 40 mL/kg/day urine output but receive insufficient electrolyte-free water 4
• Excessive sodium administration: Patients receiving sodium bicarbonate, mannitol, or hypertonic saline are at high risk 4
• Impaired water access: Sedation, intubation, altered mental status prevent thirst-driven water intake 3, 8
• Associated conditions: Sepsis, renal dysfunction, hypoalbuminemia, and hypokalaemia increase risk 4

Traumatic Brain Injury Patients

• Avoid prolonged induced hypernatremia for intracranial pressure control due to risk of "rebound" ICP during correction 6, 5
• The relationship between serum sodium and ICP is weak, and rapid regulation of brain cell volume limits effectiveness of prolonged hyperosmolarity 6
• Hypernatremia with hyperchloremia may impair renal function 6, 5

Clinical Significance

• Mortality impact: Hypernatremia is an independent risk factor for increased mortality in critically ill patients 2, 3
• Length of stay: Any degree of hypernatremia increases ICU and hospital length of stay 2
• Post-discharge outcomes: Persistent hypernatremia is associated with increased post-discharge mortality 2

Common Pitfalls to Avoid

• Using isotonic fluids in patients with renal concentrating defects (e.g., nephrogenic diabetes insipidus) worsens hypernatremia 1
• Overcorrecting with excessive sodium-containing fluids when positive fluid balance exists—these patients need electrolyte-free water, not more sodium 4
• Failing to account for ongoing losses when calculating replacement needs 1
• Inadequate monitoring leading to overly rapid correction 5