How to manage a patient with hypernatremia (elevated sodium level) of 155 mmol/L?

Management of Hypernatremia 155 mmol/L

For a sodium level of 155 mmol/L, correct the hypernatremia gradually with hypotonic fluids (0.45% NaCl or D5W) at a rate not exceeding 10 mmol/L per 24 hours (or 0.4 mmol/L/hour), while simultaneously identifying and treating the underlying cause. 1, 2, 3

Initial Assessment

Determine the acuity and underlying etiology:

• Acute hypernatremia (<24-48 hours): Often iatrogenic from hypertonic saline/bicarbonate administration, can be corrected more rapidly 1, 3
• Chronic hypernatremia (>48 hours): Requires slow correction to prevent cerebral edema; limit to 8-10 mmol/L per day 1, 3

Assess volume status to guide fluid selection: 3

• Hypovolemic: Renal losses (osmotic diuresis, diabetes insipidus) or extrarenal losses (GI losses, burns, excessive sweating) 3
• Euvolemic: Diabetes insipidus (central or nephrogenic), inadequate water intake, impaired thirst mechanism 3
• Hypervolemic: Excessive sodium intake (rare), primary hyperaldosteronism 3

Check urine osmolality to differentiate causes: 3

• Urine osmolality >600-800 mOsm/kg suggests extrarenal water loss 3
• Urine osmolality <300 mOsm/kg suggests diabetes insipidus 3

Fluid Replacement Strategy

Calculate free water deficit using the formula: 2, 3

Free water deficit = 0.6 × body weight (kg) × [(current Na/140) - 1]

Select appropriate hypotonic fluid: 1, 2, 3

• D5W (5% dextrose in water): Preferred for severe hypernatremia as it delivers no osmotic load and allows controlled sodium decrease 1, 2
• 0.45% NaCl (half-normal saline): Alternative for moderate hypernatremia, provides some sodium replacement 2, 3
• Avoid isotonic saline (0.9% NaCl): Will worsen hypernatremia as it delivers excessive osmotic load requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid 1

Administer fluids at controlled rate: 1, 2, 3

• Chronic hypernatremia: Reduce sodium by maximum 8-10 mmol/L per 24 hours (0.4 mmol/L/hour) 1, 3
• Acute hypernatremia (<24 hours): Can correct more rapidly, but still monitor closely 1, 3
• Initial fluid rate: 25-30 mL/kg/24 hours for adults 2

Specific Etiology-Based Management

For diabetes insipidus (central): 1, 3

• Administer desmopressin (DDAVP/Minirin) in addition to hypotonic fluids 1, 3
• Typical dose: 1-4 mcg subcutaneously or intravenously 3

For nephrogenic diabetes insipidus: 3

• Discontinue offending medications (lithium, demeclocycline) if possible 3
• Correct underlying electrolyte abnormalities (hypokalemia, hypercalcemia) 3
• Ongoing hypotonic fluid administration required to match excessive free water losses 3

For hypervolemic hypernatremia: 3

• Address primary hyperaldosteronism or excessive sodium intake 3
• May require diuretics in addition to free water replacement 3

Monitoring and Safety

Close laboratory monitoring is essential: 1, 2, 3

• Check serum sodium every 2-4 hours initially during active correction 1, 2
• Adjust fluid rate based on sodium response 1, 2
• Monitor for signs of cerebral edema if correcting too rapidly (headache, confusion, seizures) 1, 3

Critical safety consideration: 1, 3

• Never correct chronic hypernatremia faster than 10 mmol/L per 24 hours to avoid cerebral edema from rapid osmotic shifts 1, 3
• Rapid correction is only appropriate for acute hypernatremia (<24 hours duration) 1, 3

Special Considerations

For acute severe hypernatremia requiring urgent correction: 1

• Hemodialysis is an effective option to rapidly normalize sodium levels 1
• Use with caution in chronic hypernatremia to avoid rapid sodium drop 1

For patients with impaired thirst mechanism or lack of water access: 2, 4

• Ensure adequate water access and consider nasogastric or intravenous hydration 2, 4
• Address underlying neurological or functional impairments 2

Common pitfall: Failing to recognize chronic vs. acute hypernatremia leads to overly rapid correction and cerebral edema 1, 3