How should hypernatremia be managed in an adult patient with a serum sodium level of 148 mmol/L?

Management of Mild Hypernatremia (Sodium 148 mmol/L)

A serum sodium of 148 mmol/L represents mild hypernatremia that warrants investigation of the underlying cause and careful correction, but typically does not require aggressive intervention unless the patient is symptomatic or has rapid onset. 1

Initial Assessment

Determine the chronicity and volume status immediately, as this guides your correction strategy:

• Assess for hypovolemia: Look for orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia, and reduced urine output 1
• Assess for hypervolemia: Check for peripheral edema, ascites, jugular venous distention, and pulmonary congestion 1
• Measure urine osmolality and sodium: A urine osmolality of <300 mOsm/kg with hypernatremia suggests impaired renal concentrating ability or diabetes insipidus 1
• Calculate fluid balance: Review intake/output records and recent weight changes to determine if this represents water loss versus sodium gain 2

Treatment Algorithm Based on Volume Status

For Hypovolemic Hypernatremia (Most Common)

Administer hypotonic fluids to replace free water deficit 1:

• First-line fluid: 0.45% NaCl (half-normal saline) containing 77 mEq/L sodium 1
• Alternative: 0.18% NaCl (quarter-normal saline) for more aggressive free water replacement 1
• Never use isotonic saline (0.9% NaCl) as initial therapy, as this will worsen hypernatremia, particularly in patients with renal concentrating defects 1

For Euvolemic Hypernatremia

• Provide free water replacement via oral route if possible, or D5W intravenously 1
• Consider low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) 1

For Hypervolemic Hypernatremia

• Implement fluid restriction to 1.5-2 L/day 1
• Consider diuretics to promote negative sodium balance while providing free water replacement 3

Correction Rate Guidelines

The maximum safe correction rate is 10-15 mmol/L per 24 hours for chronic hypernatremia (>48 hours duration) 1:

• For sodium 148 mmol/L: Target reduction to approximately 138-143 mmol/L over 24 hours
• Monitor serum sodium every 2-4 hours initially during active correction, then every 6-12 hours 1
• Acute hypernatremia (<48 hours) can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 1

Correcting chronic hypernatremia too rapidly causes cerebral edema, seizures, and permanent neurological injury because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions 1

Common Underlying Causes to Address

• Inadequate water intake: Ensure access to free water, especially in elderly or cognitively impaired patients 4
• Excessive sodium administration: Review all IV fluids, medications, and sodium bicarbonate use 2
• Renal water losses: Polyuria from osmotic diuresis, diabetes insipidus, or diuretic use 2
• Extrarenal losses: Diarrhea, burns, or excessive sweating 4

Critical Monitoring Parameters

• Daily weights and strict intake/output monitoring 1
• Serum electrolytes including potassium, chloride, and bicarbonate 1
• Urine output, specific gravity, and osmolality to assess renal response 1
• Neurological status: Watch for confusion, lethargy, seizures, or focal deficits 4

Special Populations

In critically ill patients, hypernatremia is an independent risk factor for mortality and develops because various factors promote renal water loss, which is then inadequately corrected or overcorrected with relatively hypertonic fluids 2:

• Sepsis, renal dysfunction, and hypoalbuminemia are independent risk factors 2
• Therapy should rely on adding electrolyte-free water and/or creating a negative sodium balance 2

In patients with heart failure, limit fluid intake to around 2 L/day and avoid excessive fluid administration 1

In cirrhotic patients, evaluate for hypovolemic versus hypervolemic state and provide appropriate fluid resuscitation or restriction accordingly 1