What is the best approach to treat a patient with hypernatremia?

Hypernatremia Treatment

Immediate Treatment Approach

For hypernatremia, replace free water deficits with hypotonic fluids (0.45% NaCl or D5W) at a correction rate not exceeding 10-15 mmol/L per 24 hours for chronic cases, while simultaneously addressing the underlying cause. 1

Initial Assessment and Diagnosis

Before initiating treatment, determine three critical factors:

• 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
• Determine chronicity: acute (<24-48 hours) versus chronic (>48 hours), as this dictates correction speed 2, 1
• Measure urine osmolality and sodium: inappropriately dilute urine (<300 mOsm/kg) suggests diabetes insipidus or impaired concentrating ability, while concentrated urine indicates extrarenal losses 1

Calculate the free water deficit using: Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) 1

Fluid Selection Strategy

The choice of replacement fluid depends on severity and clinical context:

• 0.45% NaCl (half-normal saline) contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 1
• 0.18% NaCl (quarter-normal saline) contains ~31 mEq/L sodium, providing more aggressive free water replacement for severe cases 1
• D5W (5% dextrose in water) delivers no renal osmotic load and allows controlled decrease in plasma osmolality, making it the preferred choice for severe hypernatremia 1

Never use isotonic saline (0.9% NaCl) as initial therapy, as it delivers excessive osmotic load requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid, which worsens hypernatremia 1

Correction Rate Guidelines

The speed of correction is critical to prevent cerebral edema:

• Chronic hypernatremia (>48 hours): maximum correction of 10-15 mmol/L per 24 hours 1, 2, 3
• Acute hypernatremia (<24 hours): can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 1
• Corrections faster than 48-72 hours have been associated with increased risk of pontine myelinolysis 1

Slower correction of chronic hypernatremia is critical because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions, and rapid correction can cause cerebral edema, seizures, and permanent neurological injury. 1

Special Clinical Scenarios

Nephrogenic Diabetes Insipidus

• Avoid isotonic saline entirely as this will worsen hypernatremia in patients with renal concentrating defects 1
• Requires ongoing hypotonic fluid administration to match excessive free water losses 1
• Consider desmopressin only for central diabetes insipidus, not nephrogenic 1

Heart Failure Patients

• Implement sodium and fluid restriction, limiting fluid intake to around 2 L/day for most hospitalized patients 1
• Consider vasopressin antagonists (tolvaptan, conivaptan) for short-term use in persistent severe hypernatremia with cognitive symptoms 1
• After initial correction, fluid restriction (1.5-2 L/day) may be needed with careful monitoring 1

Cirrhosis Patients

• Evaluate for hypovolemic versus hypervolemic state first 1
• For hypovolemic hypernatremia: provide fluid resuscitation with hypotonic solutions 1
• For hypervolemic hypernatremia: focus on attaining negative water balance rather than aggressive fluid administration, discontinue IV fluids and implement free water restriction 1

Severe Burns or Voluminous Diarrhea

• Requires hypotonic fluids to match ongoing free water losses 1
• Fluid composition should be matched to losses while providing adequate free water 1

Monitoring Protocol

Frequent monitoring is essential to prevent complications:

• Check serum sodium every 2-4 hours initially during active correction, then every 6-12 hours 1
• Monitor daily weight and supine/standing vital signs 1
• Track fluid input and output with careful attention to urine output, specific gravity/osmolarity, and urine electrolyte concentrations 1
• Assess for signs of cerebral edema: confusion, seizures, altered mental status 2, 3

Common Pitfalls to Avoid

• Correcting chronic hypernatremia too rapidly leads to cerebral edema, seizures, and neurological injury 1, 2
• Using isotonic saline in patients with renal concentrating defects exacerbates hypernatremia 1
• Inadequate monitoring during correction results in overcorrection or undercorrection 1
• Failing to identify and treat the underlying cause, which is often iatrogenic, especially in vulnerable populations 1
• Prolonged induced hypernatremia to control ICP in traumatic brain injury is not recommended, as it requires an intact blood-brain barrier and may worsen cerebral contusions 1

High-Risk Populations

Older Adults

• At higher risk for both hypernatremia and complications from correction due to reduced renal function affecting sodium and water handling 1
• Cognitive impairment may prevent recognition of thirst or ability to access fluids 1
• Restrict sodium intake cautiously, as excessive restriction may paradoxically worsen nutritional status 1

Pediatric Patients

• Hypernatremia mostly results from incorrect replacement of transepidermal water loss, inadequate water intake, or excessive sodium intake 1
• Replace plasma volume first in symptomatic hypovolemia before addressing hypernatremia 1
• Neonates require particularly careful assessment of intravascular volume and hydration status 1

ICU Patients

• At high risk due to inability to control free water intake from sedation, intubation, altered mental status, and fluid restriction 4
• Excessive fluid losses from renal or nonrenal sources and treatment with sodium-containing fluids commonly predispose to hypernatremia 4
• Free water requirements should be routinely assessed and judicious electrolyte and free water replacement prescribed 4