Episode 198: Hypernatremia

We discuss the approach to diagnosing and managing hypernatremia in the emergency department.

Abigail Olinde, MD
Brian Gilberti, MD

July 1st, 2024 Download Leave a Comment Tags:

Show Notes

Episode Overview:

  • Introduction to Hypernatremia
  • Definition and basic concepts
  • Clinical presentation and risk factors
  • Diagnosis and management strategies
  • Special considerations and potential complications

Definition and Pathophysiology:

  • Hypernatremia is defined as a serum sodium level over 145 mEq/L.
  • It can be acute or chronic, with chronic cases being more common.
  • Symptoms range from nausea and vomiting to altered mental status and coma.

Causes of Hypernatremia based on urine studies:

  • Urine Osmolality > 700 mosmol/kg
    • Causes:
      • Extrarenal Water Losses: Dehydration due to sweating, fever, or respiratory losses
      • Unreplaced GI Losses: Vomiting, diarrhea
      • Unreplaced Insensible Losses: Burns, extensive skin diseases
      • Renal Water Losses with Intact AVP Response:
      • Diuretic phase of acute kidney injury
      • Recovery phase of acute tubular necrosis
      • Postobstructive diuresis
  • Urine Osmolality 300-600 mosmol/kg
    • Causes:
      • Osmotic Diuresis: High glucose (diabetes mellitus), mannitol, high urea
      • Partial AVP Deficiency: Incomplete central diabetes insipidus
      • Partial AVP Resistance: Nephrogenic diabetes insipidus
  • Urine Osmolality < 300 mosmol/kg
    • Causes:
      • Complete AVP Deficiency: Central diabetes insipidus
      • Complete AVP Resistance: Nephrogenic diabetes insipidus
  • Urine Sodium < 25 mEq/L
    • Causes:
      • Extrarenal Water Losses with Volume Depletion: Vomiting, diarrhea, burns
      • Unreplaced Insensible Losses: Sweating, fever, respiratory losses
  • Urine Sodium > 100 mEq/L
    • Causes:
      • Sodium Overload: Ingestion of salt tablets, hypertonic saline administration
      • Salt Poisoning: Deliberate or accidental ingestion of large amounts of salt
  • Mixed or Variable Urine Sodium
    • Causes:
      • Diuretic Use: Loop diuretics, thiazides
      • Adrenal Insufficiency: Mineralocorticoid deficiency
      • Osmotic Diuresis with Renal Water Losses: High glucose, mannitol

Risk Factors:

  • Patients with impaired thirst response or those unable to access water (e.g., altered or ventilated patients) are at higher risk.
  • Important to consider underlying conditions affecting thirst mechanisms.


  • Initial assessment includes history, physical examination, and laboratory tests.
  • Key tests: urine osmolality and urine sodium levels.
  • Lab errors should be considered if the clinical picture does not match the lab results.

Management Strategies:

  • Calculate the Free Water Deficit (FWD) to guide treatment. 

  • Administration routes include oral, NGT, G-tube, or IV with D5W for larger deficits.
  • Safe correction rate is 10-12 mEq/L per day or 0.5 mEq/L per hour to avoid cerebral edema.
  • Address hypovolemia with isotonic fluids before correcting sodium.

Monitoring and Follow-Up:

  • Monitor sodium levels every 4-6 hours.
  • Assess urine output and adjust free water administration as needed.
  • Admission to ICU for symptomatic patients or those with severe hypernatremia (sodium >160 mEq/L).
  • Decision to discharge vs admit is a complicated one that factors in symptoms, etiology, degree of hypernatremia, patient preference, access to follow up, etc.

Take Home Points:

  • Hypernatremia is a serum sodium level over 145 mEq/L, with symptoms ranging from nausea to coma.
  • It is primarily caused by water loss exceeding intake due to various factors like sweating, vomiting, diarrhea, and renal issues.
  • Correcting hypernatremia too quickly can lead to cerebral edema, so a safe correction rate is essential.
  • Initial treatment involves calculating the Free Water Deficit and selecting the appropriate administration route.
  • Monitor sodium levels frequently and decide on admission or discharge based on symptoms, sodium levels, and patient’s ability to follow up.

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