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Source: Coyle JD, Matzke GR. Disorders of Sodium and Water Homeostasis. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. Accessed August 18, 2012.

  • Serum sodium >145 mEq/L (>145 mmol/L)

  • Results from deficit of water relative to extracellular fluid (ECF) sodium content.
  • Most commonly seen in patients with impaired thirst response or without access to water.

  • Homeostasis: Physiologic processes that maintain relatively stable equilibrium between interdependent elements.
    • Mechanisms for regulating blood volume and plasma osmolality involve control of sodium and water balance.
      • Homeostatic mechanisms for controlling blood volume focused on controlling sodium balance.
      • Plasma osmolality largely determined by serum sodium concentration and controlled by water balance.
      • 60% of total body water distributed intracellularly; 40% contained in extracellular space.
        • Sodium, chloride, and bicarbonate comprise >90% of total osmolality of ECF.
        • Intracellular osmolality depends primarily on concentration of potassium.
  • Insensible water loss in patients deprived of water (e.g., mechanical ventilation) may result in hypernatremia.
  • Diabetes insipidus (DI) causes excretion of large volumes of dilute urine/day.
    • Classified as central (decreased arginine vasopressin [AVP] secretion) or nephrogenic (decreased renal response to AVP).
  • Iatrogenic administration of hypertonic sodium chloride results in hypernatremia and expanded ECF volume.

  • Incidence in general medical-surgical hospital patients: 1% to ~8%.
    • Majority of cases are hospital acquired.

  • Awareness of potential for hypernatremia in mechanically ventilated patients
  • Intact thirst mechanism

  • Age
    • Infants
    • Elderly or disabled patients with impaired sensorium or functional status
  • Diuretic therapy
  • Use of mechanical ventilators

Signs and Symptoms

  • Symptoms related to decrease in neuronal cell volume:
    • Weakness
    • Lethargy
    • Restlessness
    • Irritability
    • Confusion
  • Symptoms related to more severe (serum sodium >160 mEq/L [>160 mmol/L]) or rapid development:
    • Twitching
    • Seizures
    • Coma
    • Death
  • Signs:
    • Postural hypotension
    • Tachycardia
    • Dry oral mucosa
    • Diminished skin turgor

Means of Confirmation and Diagnosis

  • Serum sodium value >145 mEq/L (>145 mmol/L)

Laboratory Tests

  • Metabolic panel
  • Plasma osmolality
  • Urine osmolality: to differentiate renal from nonrenal water loss

Differential Diagnosis

  • Resolve underlying cause.
  • Normalize ECF volume.
  • Safely correct hypernatremia.
    • Rapid correction can result in movement of excessive water into brain cells, resulting in:
      • Cerebral edema
      • Seizures
      • Neurologic damage
      • Death

  • Hypovolemia hypernatremia
    • Restore hemodynamic stability with normal saline infusion.
      • Rate of infusion depends on how rapidly hypernatremia developed.
        • Over a few hours: ~1 mEq/L (1 mmol/L) per hour
        • Slower onset: 0.5 mEq/L (0.5 mmol/L) per hour
        • Do not exceed 10 mEq/L (10 mmol/L) per day.
    • Hyperglycemia-induced: correct hyperglycemia with insulin and administer normal saline.
  • Central DI (Table 1)
    • Treat with intranasal desmopressin, beginning with 10 mcg/day and titrating as needed, usually to 10 mcg twice daily
  • Nephrogenic DI
    • Decrease ECF volume with thiazide diuretic.
    • Restrict dietary sodium (2000 mg/day)
    • Treatment with drugs with antidiuretic properties (Table 1).
  • Sodium overload
    • Treat with loop diuretics (furosemide 20–40 mg IV every 6 hours) ...

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