What is the treatment plan for a patient with hypernatremia, considering their age, medical history, and severity of symptoms?

Hypernatremia Treatment

Immediate Assessment and Classification

For hypernatremia (serum sodium >145 mmol/L), immediately determine the chronicity (acute <48 hours vs. chronic >48 hours) and volume status (hypovolemic, euvolemic, or hypervolemic), as this dictates both the correction rate and fluid choice. 1, 2

• Acute hypernatremia (<48 hours) can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic, because brain cells have not yet synthesized intracellular osmolytes 1
• Chronic hypernatremia (>48 hours) requires slower correction at 10-15 mmol/L per 24 hours maximum to prevent cerebral edema, seizures, and permanent neurological injury 1, 3, 4
• Assess volume status through physical examination: look for orthostatic hypotension and dry mucous membranes (hypovolemic), peripheral edema and jugular venous distention (hypervolemic), or normal volume status (euvolemic) 1

Fluid Selection Based on Volume Status

The cornerstone of hypernatremia treatment is hypotonic fluid replacement—never use isotonic saline as initial therapy, as this will worsen hypernatremia, especially in patients with renal concentrating defects. 1, 2

Hypovolemic Hypernatremia

• Administer hypotonic fluids such as 0.45% NaCl (77 mEq/L sodium) for moderate cases or 0.18% NaCl (31 mEq/L sodium) for more aggressive free water replacement 1
• D5W (5% dextrose in water) is preferred as the primary rehydration fluid because it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 1
• Avoid isotonic saline, which delivers excessive osmotic load requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid 1

Euvolemic Hypernatremia (Diabetes Insipidus)

• For nephrogenic diabetes insipidus, ongoing hypotonic fluid administration is required to match excessive free water losses—isotonic fluids will worsen hypernatremia 1, 2
• Consider low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) 1
• Desmopressin should not be used for nephrogenic DI 1

Hypervolemic Hypernatremia

• In cirrhosis patients, discontinue intravenous fluid therapy and implement free water restriction, focusing on negative water balance rather than aggressive fluid administration 1
• In heart failure patients, implement sodium and fluid restriction, limiting fluid intake to around 2 L/day 1

Correction Rate and Monitoring

The maximum correction rate for chronic hypernatremia is 10-15 mmol/L per 24 hours—faster correction risks cerebral edema because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions. 1, 3, 4

• Check serum sodium levels every 2-4 hours initially during active correction, then every 6-12 hours 1
• Monitor daily weight, vital signs, fluid input/output, and urine specific gravity/osmolarity 1, 4
• Calculate free water deficit using: Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) 1
• For acute hypernatremia (<24 hours), correction can be more rapid at up to 1 mmol/L/hour if severely symptomatic 1

Special Populations

Older Adults

• Older adults are at higher risk due to reduced renal function, cognitive impairment preventing thirst recognition, and inability to access fluids 1
• Use more cautious correction rates and closer monitoring 1

Patients with Severe Burns or Diarrhea

• Hypotonic fluids are required to keep up with ongoing free water losses 1
• Match fluid composition to losses while providing adequate free water 1

Traumatic Brain Injury

• Prolonged induced hypernatremia to control intracranial pressure 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

Critical Pitfalls to Avoid

• Never use isotonic saline (0.9% NaCl) as initial therapy—this exacerbates hypernatremia, particularly in patients with nephrogenic diabetes insipidus or renal concentrating defects 1, 2
• Never correct chronic hypernatremia faster than 10-15 mmol/L per 24 hours—rapid correction causes cerebral edema, seizures, and permanent neurological injury 1, 3
• Corrections faster than 48-72 hours have been associated with increased risk of pontine myelinolysis 1
• Inadequate monitoring during correction can result in overcorrection or undercorrection 1
• Failing to identify and treat the underlying cause (often iatrogenic in vulnerable populations) leads to recurrence 1