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Basics ⬇

Basics

Definition

Serum sodium concentration >158 mEq/L in dogs or >165 mEq/L in cats.

Pathophysiology

  • Sodium is the most abundant cation in the extracellular fluid, so hypernatremia usually reflects hyperosmolality.
  • Hypernatremia can be caused by excessive water loss, increased intake of sodium, or a combination of both.
  • Common causes of hypernatremia include renal or gastrointestinal loss of water in excess of sodium loss and low water intake.

Systems Affected

  • Endocrine/Metabolic
  • Nervous

Signalment

Dog and cat

Signs

  • Polydipsia
  • Disorientation
  • Coma
  • Seizures
  • Other findings depend on underlying cause
  • Severity of signs usually correlates to the degree of hypernatremia

Causes

  • Total body sodium high-oral ingestion (rare); IV administration of NaCl during cardiovascular resuscitation; hyperaldosteronism (rare); hyperadrenocorticism (may cause mild changes).
  • Total body sodium normal plus water deficit-low water intake (e.g., no access to water and adipsia or hypodipsia); high urinary water loss (e.g., diabetes insipidus); high insensible water loss (e.g., panting and hyperthermia).
  • Total body sodium low and hypotonic fluid loss (i.e., loss of fluid containing sodium without adequate water replacement)-urinary loss (e.g., diabetes mellitus, osmotic diuresis, and diuresis after acute urinary obstruction); gastrointestinal sodium loss (e.g., administration of osmotic cathartic, vomiting, and diarrhea).

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Diabetes insipidus
  • Hyperosmolar non-ketotic syndrome
  • Hypertonic dehydration
  • Alterations in thirst reaction pathway: rare
  • Salt ingestion-rare

Laboratory Findings

Drugs That May Alter Laboratory Results

A wide variety of drugs interfere with renal capacity to concentrate urine, leading to water loss in excess of sodium and high serum sodium concentration; these drugs include lithium, demeclocycline, and amphotericin.

Disorders That May Alter Laboratory Results

Lipemia or hyperproteinemia (>11 g/dL) can artifactually raise sodium concentration when the flame photometry method is used.

Valid if Run in a Human Laboratory?

Yes

CBC/Biochemistry/Urinalysis

  • High serum sodium concentration.
  • Diabetes insipidus-polyuria, low urinary specific gravity, and low urinary sodium concentration.
  • Hyperosmolar non-ketotic syndrome-high blood glucose, low urine output, and high urinary specific gravity (usually >1.025).
  • Hypertonic dehydration-low urinary sodium concentration and high urinary specific gravity (usually >1.030).

Other Laboratory Tests

  • Modified water deprivation test (see Appendix II for test protocol) to differentiate diabetes insipidus from other causes of polyuria and polydipsia; performed after results of CBC, biochemical analysis, urinalysis, and endocrine testing are evaluated to rule-out hyperadrenocorticism.
  • After water restriction, patients with diabetes insipidus have little or no increase in urinary specific gravity or osmolality.
  • After ADH or DDAVP administration, patients with nephrogenic diabetes insipidus have <10% increase in urinary specific gravity; those with central diabetes insipidus have a 10–800% increase.

Imaging

CT scan or MRI in patients with diabetes insipidus to rule out pituitary tumor.

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • If hypovolemia is severe-replace volume with isotonic saline (i.e., lactated Ringer's or normal saline) or isotonic fluids (i.e., 5% dextrose with half-normal saline).
  • Hypernatremia-administer hypotonic fluids (e.g., 5% dextrose in water) to reduce serum sodium by 0.5 mEq/h or by no more than 20 mEq/L/day; supplement with potassium and phosphate if needed.
  • Central diabetes insipidus-DDAVP (one to two drops in subconjunctival sac q12–24h).
  • Nephrogenic diabetes insipidus-hydrochlorthiazide (2–4 mg/kg PO q12h).

Contraindications

Refer to manufacturer's literature

Precautions

  • Rapid correction of hypernatremia can cause pulmonary edema.
  • Hypocalcemia may develop during correction of hypernatremia.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Acute setting-electrolytes, urine output, and body weight
  • Diabetes insipidus-water intake

Possible Complications

  • CNS thrombosis or hemorrhage.
  • Hyperactivity.
  • Seizures.
  • Serum sodium >180 mEq/L often associated with residual CNS damage.
  • Many patients recover, but possibility of neurologic damage is high.

Miscellaneous ⬆

Miscellaneous

Age-Related Factors

None

Synonyms

None

Abbreviations

  • ADH = antidiuretic hormone
  • CNS = central nervous system
  • CT = computed tomography
  • DDAVP = brand name of desmopressin, a synthetic antidiuretic hormone preparation
  • MRI = magnetic resonance imaging

Author Melinda Fleming

Consulting Editor Deborah S. Greco

Acknowledgment The author and editors acknowledge the prior contribution of Rhett Nichols.

Suggested Reading

DiBartola SP. Fluid, Electrolyte, and Acid-base Disorders in Small Animal Practice, 3rd ed. Philadelphia: Saunders, 2005.

Marks SL, Taboada J. Hypernatremia and hypertonic syndromes. Vet Clin North Am Small Anim Pract 1998, 28(3):533–543.

Ross DB. Clinical Physiology of Acid-base and Electrolyte Disorders, 3rd ed. New York: McGraw-Hill, 1989.