What is the treatment approach for a patient with hypernatremia?

Treatment Approach for Hypernatremia

For hypernatremia, administer hypotonic fluids (0.45% NaCl or D5W) to replace free water deficit, with a maximum correction rate of 10-15 mmol/L per 24 hours for chronic cases (>48 hours), while avoiding isotonic saline which will worsen the condition. 1

Initial Assessment and Classification

• Determine chronicity: Acute hypernatremia (<24-48 hours) can be corrected more rapidly (up to 1 mmol/L/hour if severely symptomatic), while chronic hypernatremia (>48 hours) requires slower correction to prevent cerebral edema 1, 2
• Assess volume status through physical examination, looking for signs of hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor) versus hypervolemia (peripheral edema, jugular venous distention) 1
• Measure urine osmolality and sodium: Inappropriately dilute urine (osmolality <300 mOsm/kg) with hypernatremia suggests diabetes insipidus or impaired renal concentrating ability 1
• Calculate free water deficit using the formula: Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) 1

Fluid Selection and Administration

• Primary fluid choice is hypotonic solution: Use 0.45% NaCl (77 mEq/L sodium) for moderate hypernatremia or 0.18% NaCl (31 mEq/L sodium) for more aggressive free water replacement 1
• D5W (5% dextrose in water) is preferred when available as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 1
• Never use isotonic saline (0.9% NaCl) as initial therapy, especially in patients with nephrogenic diabetes insipidus or renal concentrating defects, as this will worsen hypernatremia 1
• Initial infusion rate: 4-14 mL/kg/hour based on severity and clinical response 1

Correction Rate Guidelines

• For chronic hypernatremia (>48 hours): Maximum correction of 10-15 mmol/L per 24 hours (approximately 0.4 mmol/L/hour) to prevent cerebral edema, seizures, and permanent neurological injury 1, 2, 3
• For acute hypernatremia (<24 hours): Can correct more rapidly, up to 1 mmol/L/hour if severely symptomatic, as brain cells have not yet synthesized intracellular osmolytes 1
• Monitor serum sodium every 2-4 hours initially during active correction, then every 6-12 hours once stable 1

Treatment Based on Underlying Etiology

Hypovolemic Hypernatremia

• Administer hypotonic fluids (0.45% NaCl or D5W) to replace free water deficit at 4-14 mL/kg/hour 1
• Replace ongoing losses from extrarenal sources (diarrhea, burns) or renal sources (osmotic diuresis) with appropriate hypotonic fluid composition 1

Euvolemic Hypernatremia (Diabetes Insipidus)

• Central diabetes insipidus: Administer desmopressin (Minirin) in addition to hypotonic fluid replacement 2
• Nephrogenic diabetes insipidus: Requires ongoing hypotonic fluid administration to match excessive free water losses; desmopressin is ineffective 1
• Low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) may be beneficial 1

Hypervolemic Hypernatremia

• In cirrhosis: Discontinue intravenous fluid therapy and implement free water restriction, focusing on negative water balance rather than aggressive fluid administration 1
• In heart failure: Sodium and fluid restriction (1.5-2 L/day), with careful monitoring of volume status 1

Special Clinical Scenarios

Severe Hypernatremia with Altered Mental Status

• Combine IV hypotonic fluids with free water via nasogastric tube if needed, targeting 10-15 mmol/L correction per 24 hours 1
• In heart failure patients: Fluid restriction (1.5-2 L/day) may be needed after initial correction, with careful monitoring 1

Traumatic Brain Injury

• Prolonged induced hypernatremia to control ICP is NOT recommended, as it requires an intact blood-brain barrier and may worsen cerebral contusions 1
• Risk of "rebound" ICP elevation exists during correction as brain cells synthesize intracellular osmolytes 1

Older Adults

• Higher risk for complications due to reduced renal function, cognitive impairment preventing recognition of thirst, and multiple comorbidities 1
• More conservative fluid rates should be used in chronic kidney disease patients, with close monitoring for worsening azotemia 1

Monitoring Protocol

• Daily monitoring: Serum electrolytes, weight, supine and standing vital signs 1
• Fluid balance tracking: Input/output, urine specific gravity/osmolarity, urine electrolyte concentrations 1
• Renal function assessment: BUN, creatinine to evaluate for worsening azotemia 1
• Adjust treatment intervals based on clinical stability after initial correction phase 1

Critical Pitfalls to Avoid

• Correcting chronic hypernatremia too rapidly (>10-15 mmol/L per 24 hours) leads to cerebral edema, seizures, and permanent neurological injury 1, 2
• Using isotonic saline in patients with renal concentrating defects will exacerbate hypernatremia 1
• Inadequate monitoring during correction can result in overcorrection or undercorrection 1
• Failing to identify and treat the underlying cause, which is often iatrogenic in hospitalized patients 1, 4
• Starting renal replacement therapy without considering sodium correction rate in patients with chronic hypernatremia can cause rapid drops in sodium concentration 2