How should hypernatremia (serum sodium 159 mEq/L) be corrected in a patient who can receive fluids only via a nasogastric tube (NGT)?

Correcting Hypernatremia (Sodium 159 mEq/L) via Nasogastric Tube

Administer free water (electrolyte-free water) via the nasogastric tube at a rate that corrects sodium by no more than 8-10 mmol/L per 24 hours, while simultaneously addressing the underlying cause of hypernatremia. 1

Immediate Assessment

• Determine volume status through clinical examination: assess for signs of hypovolemia (dry mucous membranes, decreased skin turgor, hypotension, tachycardia) versus hypervolemia (edema, jugular venous distension) to guide fluid selection 1, 2
• Check urine osmolality and urine sodium to differentiate between renal and extrarenal water losses—urine osmolality >600-800 mOsm/kg suggests extrarenal losses (diarrhea, insensible losses), while inappropriately dilute urine (<300 mOsm/kg) suggests diabetes insipidus 2, 3
• Calculate the free water deficit using: Free water deficit (L) = 0.5 × body weight (kg) × [(current Na/140) - 1], which provides your baseline replacement target 1

Fluid Selection and Administration via NGT

• Use electrolyte-free water (plain water) as the primary replacement fluid via nasogastric tube for hypernatremia correction 1, 4
• Alternatively, use 5% dextrose in water (D5W) intravenously if IV access is available, as it provides free water without sodium load 3, 5
• Avoid isotonic saline (0.9% NaCl) entirely in patients with renal concentrating defects or nephrogenic diabetes insipidus, as this will worsen hypernatremia 6, 1
• Hypotonic saline (0.45% NaCl) can be used if some sodium replacement is needed alongside free water, but pure water is preferred for severe hypernatremia 1, 2

Correction Rate and Monitoring

• Maximum correction rate: 8-10 mmol/L per 24 hours (approximately 0.5 mmol/L per hour or less) to prevent cerebral edema, seizures, and neurological injury from osmotic water shift into brain cells 1, 3
• For chronic hypernatremia (>48 hours duration), correct even more slowly over 48-72 hours to avoid cerebral edema 3, 5
• Check serum sodium every 2-4 hours initially, then every 6-8 hours once stable, adjusting the rate of free water administration based on response 1
• Monitor urine output and urine electrolytes to assess ongoing losses and adjust replacement accordingly 1

Calculating Free Water Administration Rate

• Divide the calculated free water deficit by 48-72 hours to determine hourly administration rate via NGT 3, 5
• Add ongoing free water losses (insensible losses, urine output minus electrolyte content) to the replacement rate 1
• If sodium corrects too rapidly (>0.5 mmol/L/h), slow the free water administration or add sodium-containing fluids to prevent overcorrection 1

Special Considerations for NGT Administration

• Verify NGT placement before administering free water to prevent aspiration 6
• Administer free water in divided doses throughout the day rather than large boluses to improve tolerance and absorption 4
• Monitor for gastric distension, nausea, or vomiting which may limit NGT tolerance—if these occur, consider slower administration rates or IV route 4
• In patients with diabetes insipidus, consider desmopressin (DDAVP) alongside free water replacement to reduce ongoing urinary water losses 3, 4

Addressing Underlying Causes

• Identify and treat the source of water loss: diarrhea, vomiting, fever, excessive diuretic use, diabetes insipidus, or inadequate water intake 2, 3, 5
• Ensure adequate access to water once the patient can tolerate oral intake, as hypernatremia rarely develops if patients have unrestricted access to water 5
• For diabetes insipidus, initiate desmopressin (central DI) or address the underlying cause (nephrogenic DI) while providing free water replacement 3, 4

Critical Pitfalls to Avoid

• Never correct hypernatremia faster than 8-10 mmol/L per 24 hours—too rapid correction causes cerebral edema, seizures, and potentially fatal neurological complications 1, 3, 5
• Never use isotonic saline in patients with renal concentrating defects—this delivers excessive osmotic load requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid, worsening hypernatremia 6
• Never assume the calculated deficit is the total requirement—ongoing losses must be continuously added to replacement calculations 1
• Never delay treatment while pursuing a diagnosis—begin free water replacement immediately while investigating the underlying cause 2