Hypernatremia Management in Critically Ill Patients

Initial Assessment and Treatment

The American College of Critical Care Medicine recommends immediately assessing volume status and urine electrolytes to determine the mechanism of hypernatremia, then correcting with electrolyte-free water at a rate not exceeding 8-10 mmol/L per 24 hours while addressing the underlying cause 1
The maximum correction rate for chronic hypernatremia should not exceed 8-10 mmol/L per 24 hours, with a target rate of 0.5 mmol/L per hour or less, to avoid cerebral edema, seizures, and neurological injury from osmotic water shift into brain cells 1
Isotonic fluids should be avoided in patients with renal concentrating defects, such as nephrogenic diabetes insipidus, as this worsens hypernatremia 2

Electrolyte-free water is the first-line treatment for hypernatremia, and hypotonic saline (0.45% NaCl) can be used as an alternative if some sodium replacement is needed 2
The formula for calculating free water deficit is: Free water deficit (L) = 0.5 × body weight (kg) × [(current Na/140) - 1], which provides an estimate for initial replacement, and ongoing losses must be added 1

Serial measurements of serum sodium, urine output, and urine electrolytes are required to adjust therapy and avoid complications, with serum sodium measured every 2-4 hours initially, then every 6-8 hours once stable 1
Therapy should be adjusted based on the rate of sodium correction, with slowing of free water administration or addition of sodium-containing fluids if sodium is correcting too rapidly (>0.5 mmol/L/h) 1

The American Diabetes Association suggests that the induced change in serum osmolality should not exceed 3 mOsm/kg H₂O per hour, with a maximum correction rate of 8-10 mmol/L per 24 hours or ≤0.5 mmol/L per hour 3
The Anaesthesia society recommends avoiding prolonged induced hypernatremia for intracranial pressure control in traumatic brain injury patients due to the risk of "rebound" ICP during correction, and notes that hypernatremia with hyperchloremia may impair renal function 4

Do not use isotonic saline (0.9 % NaCl) in patients with renal concentrating defects or nephrogenic diabetes insipidus, because the sodium load can exacerbate hypernatremia by requiring large urine volumes to excrete the excess osmoles. This recommendation is supported by the Pediatrics guideline (2018) and reflects a precautionary approach to fluid therapy. 5

Confirm correct nasogastric tube placement before initiating free‑water administration to prevent aspiration and related complications. This safety step is endorsed by the Clinical Nutrition guideline (2022), emphasizing the importance of verification procedures prior to enteral fluid delivery. 6