How can I safely lower a serum sodium of 157 mmol/L in a patient with hypernatremia?

Management of Severe Hypernatremia (Serum Sodium 157 mmol/L)

For a serum sodium of 157 mmol/L, you should lower it gradually using hypotonic fluids (5% dextrose or 0.45% NaCl) at a maximum correction rate of 0.4 mmol/L per hour or 10 mmol/L per 24 hours to prevent cerebral edema. 1

Immediate Assessment

Before initiating correction, determine the underlying cause and chronicity:

• Assess volume status by checking for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemic), or signs of fluid overload like edema and jugular venous distention (hypervolemic) 1
• Evaluate for diabetes insipidus if the patient has polyuria with dilute urine despite hypernatremia—this suggests either central (neurogenic) or nephrogenic causes 1
• Review medication history particularly lithium, which commonly causes nephrogenic diabetes insipidus 1
• Check for recent sodium loading from hypertonic saline or sodium bicarbonate infusions, which cause acute hypervolemic hypernatremia 1

Fluid Selection Strategy

Primary choice: 5% dextrose in water (D5W) is preferred because it delivers no renal osmotic load and allows controlled, slow decrease in plasma osmolality 2

Alternative: 0.45% NaCl (half-normal saline) containing 77 mEq/L sodium can be used for moderate hypernatremia, providing both free water and some sodium replacement 2

Avoid isotonic saline (0.9% NaCl) in hypernatremic patients as 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 2

Correction Rate Protocol

Maximum safe correction: 0.4 mmol/L per hour or 10 mmol/L per 24 hours 1

• For your patient with sodium 157 mmol/L, target reduction to approximately 147 mmol/L over the first 24 hours
• Slower correction (over 48-72 hours) is mandatory if hypernatremia developed gradually over days, as rapid correction in chronic cases increases risk of cerebral edema 1, 3
• Faster correction may be appropriate only if hypernatremia developed acutely (within hours), as this improves prognosis by preventing cellular dehydration effects 1

Initial Fluid Administration Rates

For adults: Start with 25-30 mL/kg per 24 hours of hypotonic fluid 2

Calculate free water deficit to guide total volume needed, though this is an estimate:

• Free water deficit = 0.6 × body weight (kg) × [(current Na ÷ 140) - 1]
• This calculation helps determine total replacement needs but should not dictate correction speed 3

Monitoring Requirements

• Check serum sodium every 2-4 hours initially during active correction to ensure you're not exceeding 0.4 mmol/L per hour 1, 3
• Monitor neurological status closely for signs of cerebral edema (headache, confusion, seizures) which indicates overly rapid correction 1
• Track urine output and osmolality to assess ongoing free water losses and guide replacement 1
• Measure electrolytes including potassium and glucose as these can shift during correction 3

Special Considerations by Etiology

If diabetes insipidus is present:

• Patients with nephrogenic diabetes insipidus require ongoing hypotonic fluid administration to match excessive free water losses 2
• Do not use isotonic fluids as they will worsen hypernatremia in patients unable to excrete free water appropriately 2

If hypervolemic (sodium excess):

• Consider loop diuretics to promote sodium excretion while providing hypotonic fluid replacement 1
• Address the source of sodium loading (discontinue hypertonic solutions) 1

If hypovolemic (water deficit):

• Initial resuscitation may require isotonic saline if hemodynamically unstable, then transition to hypotonic fluids once perfusion is restored 3

Critical Pitfalls to Avoid

• Never correct faster than 10 mmol/L in 24 hours—this causes cerebral edema from rapid osmotic shifts 1
• Never use hypotonic fluids in patients with raised intracranial pressure without neurosurgical consultation, as this can worsen cerebral edema 3
• Do not rely solely on formulas—clinical response and frequent sodium monitoring must guide therapy 3
• Avoid assuming chronicity—if duration is unknown, treat as chronic and correct slowly to be safe 1

The key principle is slow, controlled correction with hypotonic fluids while treating the underlying cause, with meticulous monitoring to prevent both under-correction (ongoing cellular dehydration) and over-correction (cerebral edema) 1, 3.