Hypernatremia
Serum sodium may be increased by water deprivation, excessive water losses without sufficient repletion, or excessive sodium intake. The majority of cases of this common problem are due to free water deficit rather than sodium excess. When evaluating a patient with hypernatremia, the clinician must assess the volume status to determine the etiology and subsequent treatment.
Differential Diagnosis
- Increased water loss
–GI losses (diarrhea, vomiting, intestinal fistula)
–Drugs (e.g., diuretics, alcohol, amphotericin B, phenytoin, propoxyphene, lithium, demeclocycline)
–Sweating
–Burns
–Fever
–Hyperventilation
–Diabetes insipidus (central versus
nephrogenic)
–Severe burns
–Alcohol use
–Hyperglycemia (resulting in osmotic
diuresis)
–Diuresis phase of acute renal failure
–Peritoneal dialysis
–Thyrotoxicosis
–Hyperthermia
–Adrenal or renal failure
- Decreased water intake
–Poor oral intake (e.g., in the elderly)
–Inability to swallow water due to physical
limitation (e.g., coma, access/mobility problems, swallowing problems)
–Inability to recognize the need for water
due to a hypothalamic lesion (e.g., CVA)
–Impaired thirst
–Inappropriate IV fluids (e.g., renal failure)
–Tube feeding with inadequate free water
- Excessive sodium intake
–Endocrine causes: Cushing's syndrome, ectopic ACTH, primary aldosteronism
–Iatrogenic (e.g., inappropriately administered hypertonic saline, administration of sodium bicarbonate)
–Sea water ingestion/drowning
-
Renal salt retention
–Mineralocorticoid excess (Conn's
syndrome)
–Cushing's syndrome
–Congenital adrenal hyperplasia
–Multiple myeloma
–Sjögren's syndrome
Essential hypernatremia (reset osmostat)
Workup and Diagnosis
-
Hypernatremia is defined as serum Na+>145 mEq/L; however, clinical signs and symptoms generally do not appear until serum Na+>158 mEq/L
–Severity of symptoms relates to both the acuity and magnitude of rise in Na+
History should include questions about changes in thirst and urination, recent CNS surgery, administration of IV fluids, and history of mental status changes, seizures, polyuria, thirst, diarrhea, or vomiting
Initial laboratory studies include electrolytes, BUN, creatinine, magnesium, calcium, serum and urine osmolarity, and urine Na+
–BUN/creatinine are elevated with diuretic use, glycosuria, fluid loss (e.g., GI, respiratory, skin), impaired thirst, adrenal deficiency, and DI
–Normal in hyperaldosteronism (e.g., Conn's, Cushing's, CAH)
- Assess urine osmolality
–Hyperosmolar urine (i.e., when the kidney reaction to hypernatremia is the excretion of a minimal volume of urine that is maximally concentrated) suggests an extrarenal etiology of the hypernatremia
–Urine osmolarity is decreased in renal losses (e.g., diuretics and DI) and increased in GI, respiratory, and skin losses or poor intake
- Urine Na+is elevated in renal losses (>20 meq/L); decreased in GI, respiratory, and skin losses or poor intake (<10 meq/L); and normal in hyperaldosteronism
Treatment
-
Patients with severe dehydration and hypotension should be treated emergently with IV fluids (lactated Ringer's or NSS)
-
Calculate free water deficit:
0.6 ×weight (kg) ×[(Na+measured/140) – 1]
–Correct free water deficit over 48–72 hours; give patient
maintenance fluids and replacements for ongoing losses
–Reduce serum Na+by no more than 10–15 mEq/L/day
(0.5 mEq/L/hour) in chronic hypernatremia and 1
mEq/L/hr in acute hypernatremia
-
Too-rapid correction of serum Na+can precipitate seizures or cerebral edema with ensuing herniation
-
Isovolemic hypernatremia: Replace fluid with D5W (replace half of fluid deficit in the first 24 hours)
-
Hypovolemic hypernatremia: Replace fluid with NSS
-
Hypervolemic hypernatremia: Administer D5W and loop diuretics both to decrease hypertonicity by increasing Na+excretion and to add free H2O while removing volume
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Book Source Details
- Book Title: In a Page: Signs and Symptoms
- Author(s): Scott Kahan, Ellen G. Smith
- Year of Publication: 2004
- Copyright Details: In a Page: Signs and Symptoms, Copyright © 2004 Lippincott Williams & Wilkins.
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Copyright Details: In a Page: Signs and Symptoms, Copyright © 2008 Williams & Wilkins.
More About Causes of Sweating
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More About This Book:
Title: In a Page: Signs and Symptoms
Authors: Scott Kahan, Ellen G. Smith
Publisher: Lippincott Williams & Wilkins
Copyright: 2004
ISBN: 1-4051-0368-X
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» Next page: Night Sweats (In a Page: Signs and Symptoms)
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