What is the appropriate oral management for an alert adult with mild to moderate hypernatremia (serum sodium < 160 mmol/L) who can safely drink?

Oral Treatment for Hypernatremia

For an alert adult with mild to moderate hypernatremia (serum sodium < 160 mmol/L) who can safely drink, oral free water is the primary treatment, with a target correction rate not exceeding 10-12 mmol/L per 24 hours to prevent cerebral edema. 1

Initial Assessment

Before initiating treatment, determine the underlying mechanism:

• Assess volume status through physical examination looking for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia) versus peripheral edema, jugular venous distention (hypervolemia) 1
• Check urine osmolality and sodium to differentiate between water loss (urine osmolality >600-800 mOsm/kg) versus impaired water conservation (urine osmolality <300 mOsm/kg) 2
• Evaluate thirst mechanism as impaired thirst or lack of water access is a common cause in elderly patients 3

Oral Rehydration Strategy

Primary approach for mild-moderate hypernatremia:

• Administer oral free water as the first-line treatment for patients who can safely drink 1
• Calculate free water deficit using the formula: Water deficit (L) = 0.5 × body weight (kg) × [(current Na/140) - 1] to guide replacement volume 1
• Provide water in divided doses throughout the day rather than large boluses to allow gradual correction 1

Alternative oral options when pure water is not tolerated:

• Low-osmolarity oral rehydration solution (ORS) can be used safely in the presence of hypernatremia, providing both free water and some electrolyte replacement 4
• Hypotonic fluids such as diluted fruit juices or sports drinks may be better tolerated than plain water in some patients 1

Critical Correction Rate Guidelines

The rate of sodium correction is the most important safety consideration:

• Maximum correction rate: 10-12 mmol/L per 24 hours for chronic hypernatremia (>48 hours duration) to prevent cerebral edema 2, 3
• For acute hypernatremia (<24 hours): More rapid correction may be tolerated, but close monitoring remains essential 2
• Monitor serum sodium every 4-6 hours initially during active correction to ensure the rate stays within safe limits 1

Treatment Based on Underlying Cause

Hypovolemic hypernatremia (most common):

• Oral free water plus sodium replacement if losses are from gastrointestinal sources (diarrhea, vomiting) 1
• ORS providing 50-100 mL/kg over 3-4 hours for adults with concurrent volume depletion 4
• Replace ongoing losses with additional ORS (ad libitum, up to ~2 L/day) as long as losses continue 4

Euvolemic hypernatremia (diabetes insipidus):

• Oral free water alone is sufficient if the patient has intact thirst and water access 1
• Patients with impaired thirst require scheduled water intake rather than relying on thirst-driven consumption 3

Hypervolemic hypernatremia (rare, sodium excess):

• Oral free water with sodium restriction to 2000 mg per day (88 mmol per day) 4
• Avoid additional sodium intake while providing adequate free water 1

When Oral Treatment is Insufficient

Indications to switch to intravenous therapy:

• Severe symptoms including altered mental status, confusion, seizures, or coma require immediate IV hypotonic fluids 1, 5
• Inability to tolerate oral intake due to nausea, vomiting, or impaired consciousness 4
• Serum sodium ≥160 mmol/L typically requires IV management for more controlled correction 1
• Failure of oral rehydration demonstrated by persistent or worsening hypernatremia after 24 hours 1

Special Populations Requiring Caution

Elderly patients:

• Impaired thirst mechanism is common, requiring scheduled rather than ad libitum water intake 3
• Higher risk of cerebral edema with rapid correction due to brain adaptation to chronic hypertonicity 3

Patients with renal concentrating defects:

• Nephrogenic diabetes insipidus requires ongoing hypotonic fluid administration to match excessive free water losses 4
• Avoid isotonic fluids as they will worsen hypernatremia in patients unable to excrete free water appropriately 4

Common Pitfalls to Avoid

• Correcting chronic hypernatremia too rapidly (>10-12 mmol/L per 24 hours) can cause cerebral edema, seizures, and permanent neurological damage 2, 3
• Using isotonic saline in hypernatremic patients delivers excessive osmotic load requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid 6
• Failing to address the underlying cause (e.g., uncontrolled diabetes insipidus, ongoing diarrhea) leads to recurrent hypernatremia 1, 5
• Inadequate monitoring during correction can miss overly rapid sodium decline or persistent hypernatremia 1, 5
• Relying on thirst alone in elderly or cognitively impaired patients who may have absent or reduced thirst sensation 3

Monitoring During Treatment

• Check serum sodium every 4-6 hours during the first 24 hours of active correction 1
• Assess clinical response including mental status, vital signs, and urine output 5
• Track fluid intake and output to ensure adequate free water delivery 5
• Adjust water administration rate if sodium is correcting too rapidly or too slowly 1