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Clinical Case 2
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Objectives:

  • Identify causes of hypernatremia
  • Distinguish central from nephrogenic diabetes insipidus
  • Safely correct hypernatremia
  • Calculate the free water deficit in a patient with hypernatremia



1

A 79-year-old female with a history of mild dementia presents with worsening confusion over the last 2 days. She lives in a nursing home and has recently been treated with antibiotics for a urinary tract infection. You have very little information available when she presents to the ED. However, she has been healthy otherwise and is on no other medication. Her temperature is 38.1° C, pulse 90, respiratory rate 18, and blood pressure 118/60 mm Hg. She is disoriented and lethargic. Examination of the heart, lungs, and abdomen is unremarkable.

Laboratory studies are as follows: Na 165 meq/L, K 4.6 meq/L, Cl 118 meq/L, HCO3 28 meq/L, BUN 31 mg/dL, Cr 1.1 mg/dL. Urine-specific gravity is 1.030 and urine osmolality is 700 mmol/kg. Her CBC is normal.

Her hypernatremia is most likely due to:

A)Central diabetes insipidus.
B)Nephrogenic diabetes insipidus.
C)Diuretic medications.
D)Lack of free water intake and secondary dehydration.
E)Hyperglycemia.
2

This patient’s kidney function is appropriate for her hypernatremia. She is concentrating her urine, as evidenced by her high urine-specific gravity and urine osmolality. Therefore, she does not have diabetes insipidus, which is characterized by large volumes of dilute urine. Diuretic administration would result in more dilute urine if her hypernatremia were due to diuretics. Additionally, although both can occur, hyponatremia, not hypernatremia, is the more common manifestation of diuretic use. Hyperglycemia can cause an osmotic diuresis, resulting in hypernatremia, but again the urine would be dilute. See Table 5-7.

Table 5-7: Causes of Hypernatremia

  • GI loss of water
  • Osmotic diuresis
  • Osmotic diuresis
  • Excess exercise and sweating
  • Diabetes insipidus

Note: Generally, regulatory mechanisms will maintain a normal serum sodium. However, this requires access for free water. Immobile patients (especially the elderly) are particularly prone to problems because of their limited mobility and inability to independently access water.

Initial treatment for this patient should be:

A)Normal saline IV.
B)Dextrose 5% IV.
C)Sterile water IV.
D)Loop diuretics.
E)DDAVP.





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