18- hypernatremia

• Hypernatremia


  Serum Na > 145
• Hypernatremia


  • Have increased serum osmolality
  • Presents as confusion, disorientation, lethargy, seizures. If severe and uncorrected à coma and irreversible brain damage
• Causes of hypernatremia


  • Excessive sodium
  • Water deficit or dehydration
• Causes of excessive sodium


  • IV hypertonic saline
  • Sodium bicarbonate administration to correct metabolic acidosis
  • Conn's syndrome
• Causes of water deficit or dehydration

  • Loss of free water
  • Low water intake (bedridden elderly)
  • High GI or insensible water loss: sweating, burns, fever, heat stroke, pneumonia (hyperventilation), diarrhea, vomiting, osmotic diuresis (mannitol, DM)
• Determining the cause of hypernatremia


  1. Measure urine osmolality

  2. High urine osmolality (> plasma osmolality)

  3. Low urine osmolality (< plasma osmolality)
• High urine osmolality


  Indicates renal water loss à high urine volume of diluted urine with low osmolality. Do water deprivation test à Diabetes insipidus (central or nephrogenic)
• Treatment of hypernatremia


  1. Correct underlying disorder

  2. Replace water deficit slowly over 48 hours. Rapid correction à cerebral edema
• Treatment of diabetes insipidus


  1. Central: replace ADH (DDAVP)

  2. Nephrogenic: correct K and Ca, stop lithium or demeclocycline, give NSAIDs or hydrochlorothiazide if still symptomatic