What is the appropriate emergency department management for a patient with acute hypernatremia (serum sodium ≥150 mmol/L developing within the past 48 hours)?

Acute Hypernatremia Management in the Emergency Department

For acute hypernatremia (serum sodium ≥150 mmol/L developing within 48 hours), rapid correction with hypotonic fluids is safe and should be initiated immediately in the emergency department, targeting a reduction of 1 mmol/L per hour or approximately 10-12 mmol/L per 24 hours. 1

Initial Assessment and Diagnostic Workup

Upon identifying acute hypernatremia, immediately assess:

• Volume status through orthostatic vital signs, skin turgor, mucous membrane moisture, jugular venous pressure, and presence of edema 2
• Urine osmolality and sodium concentration to differentiate between water loss (urine osmolality >600 mOsm/kg) versus sodium gain (urine osmolality <300 mOsm/kg) 3
• Underlying cause including recent sodium intake, fluid losses (diarrhea, burns, diuretics), diabetes insipidus, or osmotic diuresis 2, 3
• Neurological status for confusion, altered consciousness, seizures, or coma, which indicate severe hypernatremia requiring urgent intervention 2

Fluid Selection and Administration

The primary treatment is hypotonic fluid replacement:

• For severe acute hypernatremia (>170 mmol/L): Administer 5% dextrose in water (D5W) as the preferred initial fluid, as it delivers no renal osmotic load and allows controlled plasma osmolality reduction 4, 2
• For moderate acute hypernatremia (150-170 mmol/L): Use 0.45% NaCl (half-normal saline) or D5W depending on volume status 4
• 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 fluid, potentially worsening hypernatremia 5

Correction Rate Guidelines

The critical distinction between acute and chronic hypernatremia determines correction speed:

• Acute hypernatremia (<24-48 hours): Rapid correction at 1 mmol/L per hour or 10-12 mmol/L per 24 hours is safe and not associated with increased mortality or cerebral edema 1, 6
• Chronic hypernatremia (>48 hours): Limit correction to 8-10 mmol/L per day to prevent cerebral edema from osmotic shifts 4, 3
• In critically ill patients with acute hypernatremia: A landmark study of 449 ICU patients found no evidence that rapid correction (>0.5 mmol/L per hour) increased mortality, seizures, altered consciousness, or cerebral edema compared to slower correction 1

Specific Clinical Scenarios

Massive Sodium Ingestion

• For acute severe hypernatremia from salt ingestion: Aggressive free-water replacement with up to 6 liters over 30 minutes has been successful in cases with sodium levels as high as 196 mmol/L 6
• Consider hemodialysis for extremely severe acute cases (sodium >180 mmol/L) to rapidly normalize levels 4

Diabetes Insipidus

• Central diabetes insipidus: Administer desmopressin (Minirin) in addition to free-water replacement 4
• Nephrogenic diabetes insipidus: Requires ongoing hypotonic fluid administration to match excessive free-water losses; isotonic fluids will worsen hypernatremia 5

Volume-Depleted Patients

• Initial resuscitation: May require isotonic saline briefly to restore hemodynamic stability, then switch to hypotonic fluids once blood pressure stabilizes 3
• Calculate free-water deficit: Use the formula: Free-water deficit = 0.6 × body weight (kg) × [(current Na/140) - 1] to guide total replacement volume 3

Monitoring Requirements

Close laboratory surveillance is essential:

• Check serum sodium every 2-4 hours during active correction to ensure appropriate rate and avoid overcorrection 4, 2
• Monitor for neurological changes including altered mental status, seizures, or signs of cerebral edema 2
• Assess volume status repeatedly to guide ongoing fluid selection and rate 3
• Track urine output and osmolality to evaluate response to treatment 3

Common Pitfalls to Avoid

• Do not apply chronic correction rates to acute hypernatremia – the 8-10 mmol/L per day limit is for chronic cases; acute hypernatremia can be corrected much faster safely 1, 4
• Do not use isotonic saline as primary treatment for hypernatremia, as it provides inadequate free water and may worsen the condition 5
• Do not delay treatment while awaiting additional workup in symptomatic patients; begin hypotonic fluid replacement immediately 2
• Do not assume all hypernatremia requires slow correction – the rapidity of development determines safe correction speed, not the absolute sodium level 1, 3

Special Considerations for ED Disposition

• Admit to ICU patients with severe hypernatremia (>160 mmol/L), altered mental status, or requiring rapid correction 3
• Admit to monitored bed patients with moderate hypernatremia (150-160 mmol/L) requiring ongoing hypotonic fluid therapy 2
• Ensure clear correction plan is communicated to admitting team, specifying target correction rate based on acuity 4

The key principle distinguishing acute from chronic hypernatremia management is that acute hypernatremia (developing within 48 hours) can and should be corrected rapidly without the cerebral edema risk seen in chronic cases, as the brain has not yet adapted through osmolyte accumulation 1, 3.