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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • A serum sodium concentration greater than the upper limit in normal horses is generally >144 mEq/L
  • Sodium is the major extracellular cation in the body, and therefore, is critical for maintenance of the extracellular space
  • Serum sodium concentration reflects the ratio of whole-body sodium to whole-body water; therefore, knowledge of the hydration state is important for accurate interpretation of serum sodium concentrations
  • Hypernatremia usually reflects an absolute or relative water deficiency
  • Systems affected—nervous: hypernatremia may lead to hyperosmolality and intracellular water loss from neurons, in turn leading to central nervous system shrinkage

Signalment!!navigator!!

Any breed, age, or sex.

Signs!!navigator!!

  • Lethargy
  • Weakness
  • Seizures
  • Coma
  • Death
  • Severity of signs depends on the duration and degree of hypernatremia
  • Other signs depend on the underlying cause

Causes and Risk Factors!!navigator!!

  • Normal whole-body sodium with pure water loss—water deprivation because of unavailable water source or physical abnormality causing decreased ingestion (e.g. botulism or dysphagia); prolonged hyperventilation; central and nephrogenic DI; evaporative loss from extensive burns; exhausted horse syndrome
  • Low whole-body sodium with hypotonic fluid loss—urinary loss (osmotic diuresis, e.g., osmotic diuretic administration such as mannitol); gastrointestinal loss (early stages of diarrhea, before the point of compensatory water intake occurs)
  • High whole-body sodium—excessive sodium chloride intake (i.e. salt poisoning) with water restriction; IV or oral administration of hypertonic saline or sodium bicarbonate solutions

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • History or physical examination to detect decreased water intake or excessive water loss resulting in (hypertonic) dehydration
  • See Causes and Risk Factors

CBC/Biochemistry/Urinalysis!!navigator!!

  • High serum sodium concentration
  • Hyposthenuria—consider DI
  • Decreased potassium, chloride, calcium, and magnesium; stress neutrophilia and lymphopenia, occasionally leukopenia—consider exhausted horse syndrome

Other Laboratory Tests!!navigator!!

  • Urinary FENa—a single urine sample can be used for sodium and creatinine measurements, which are compared with serum sodium and creatinine concentrations determined at the same time ([Na+u/Na+s]/[Cru/Crs]; normal <1%); suspect extrarenal water loss if urine volume with FENa <1% and clinical signs of dehydration; suspect osmotic diuresis if urine volume is increased with an FENa >1% and clinical signs of dehydration.
  • Plasma osmolality—should be high with hypernatremia
  • Other laboratory tests depend on the underlying cause:
    • ADH (vasopressin) blood concentration in conjunction with water deprivation—nephrogenic DI if vasopressin ≥3; neurogenic DI or not DI if vasopressin is normal
    • The ADH response test with vasopressin administered IV, and urine osmolality measured at 2 h intervals—neurogenic DI if urine osmolality/urine specific gravity increases to ≥1.025

Imaging!!navigator!!

N/A

Other Diagnostic Procedures!!navigator!!

N/A

Treatment ⬆ ⬇

TREATMENT

  • Treatment depends on the severity of hypernatremia and the underlying disorder
  • If increases in sodium and chloride are proportional, administer IV fluids such that decreases in serum sodium concentration do not exceed 0.5 mEq/L/h
  • If chloride is increased disproportionately compared with sodium, evaluate and treat the acid–base imbalance

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Treat the underlying disorder.

Contraindications/Possible Interactions!!navigator!!

The combination of hypernatremia and dehydration is a therapeutic dilemma because rapid reduction of serum sodium concentrations can lead to cerebral and pulmonary edema. Decreases in serum sodium concentration should not exceed 0.5 mEq/L/h.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Electrolytes, acid–base status, urine output, water intake, and body weight.

Possible Complications!!navigator!!

Seizures, convulsions, and probable permanent neurologic damage in severe, longstanding cases, or with rapid correction of serum sodium concentrations.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Abbreviations!!navigator!!

Suggested Reading ⬆ ⬇

George JW, Zabolotzky SM. Water, electrolytes, and acid base. In: Latimer KS, ed. Duncan & Prasse's Veterinary Laboratory Medicine Clinical Pathology, 5e. Hoboken, NJ: Wiley Blackwell, 2011:146–147.

Jose-Cunilleras E. Abnormalities of body fluids and electrolytes in athletic horses. In: Hinchcliff KW, Kaneps AJ, Geor RJ, eds. Equine Sports Medicine and Surgery, 2e. Philadelphia, PA: Saunders, 2013:881–885.

Author(s) ⬆

Authors: Wendy S. Sprague and Martin David

Consulting Editor: Sandra D. Taylor