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hyponatremia
HYPONATREMIA

Hyponatremia is serum sodium concentration <135 mEq/L due to failure of normal water excretion.

Most common causes are medication effects, fluid retention and syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Volume status should be assessed to help determine the underlying cause.

Commonly, patients with hyponatremia are asymptomatic and it is only an incidental finding.

 

Hyponatremia Signs and Symptoms

Definition

  • Serum sodium concentration <135 mEq/L due to failure of normal water excretion
    • Severe hyponatremia is when there is <120 mEq/L serum sodium concentration

Etiology

  • Most common causes are medication effects, fluid retention and syndrome of inappropriate antidiuretic hormone secretion (SIADH)

Signs and Symptoms

  • Commonly, patients with hyponatremia are asymptomatic and it is only an incidental finding
  • Gradual decrease in sodium usually shows minimal symptoms whereas rapid decreases manifest severe symptoms
    • Severe symptoms are due to brain edema and increased intracranial pressure
  • Mild to moderate symptoms that are relatively nonspecific and occur most commonly in patients with severe chronic hyponatremia are the following:
    • Headache
    • Fatigue
    • Lethargy
    • Nausea and vomiting
    • Dizziness
    • Gait disturbances
    • Forgetfulness
    • Confusion
    • Muscle cramps
  • Severe symptoms include seizures, obtundation, coma and respiratory arrest
  • Acute intervention is needed if the following symptoms occur:
    • Polydipsia
    • Muscle cramps
    • Headaches
    • Falls
    • Confusion
    • Altered mental status
    • Obtundation
    • Coma
    • Status epilepticus

Epidemiology

  • Hyponatremia is the most common body fluid disorder and electrolyte imbalance encountered in clinical practice
    • Accounts for 15-30% of emergency admissions in hospital and associated with increased morbidity, mortality and length of hospital stay in patients presenting with a range of conditions
    • Increases risk of falls and osteoporosis and in severe cases it can be associated with mental state changes, including risk of coma and seizures

Pathophysiology

  • Osmolality (total concentration of solutes in water) of plasma plays a role in the pathophysiology of hyponatremia
  • Arginine vasopressin [antidiuretic hormone (ADH)] system and thirst strict regulation help maintain plasma osmolality
  • Increase in plasma osmolality leads to ADH secretion and water retention which decreases serum osmolality
  • Decrease in plasma osmolality decreases ADH that will result in diuresis of free water and a return to homeostasis
  • Hyponatremia is a disorder of water imbalance where there is a relative excess of body water compared to total body sodium and potassium content due to impaired renal water excretion
    • Usually associated with disturbance in the ADH that governs water balance
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