9. Hyponatremia and Hypernatremia

• What measurement is used to evaluate a patient’s fluid status?

  Plasma sodium concentration
• Why is plasma sodium concentration a reasonable indicator of plasma osmolarity?

  It accounts for over 90% of extracellular solute
• What is the normal plasma sodium concentration?

  About 142 mEq/L
• What condition is indicated by a plasma sodium concentration reduced below normal?

  Hyponatremia
• What condition is indicated by a plasma sodium concentration elevated above normal?

  Hypernatremia
• What are the causes of hyponatremia?

  • Loss of sodium chloride
  • Addition of excess water
  • Diarrhea and vomiting
  • Overuse of diuretics
  • Addison’s disease
• What happens when plasma sodium concentration decreases?

  It can lead to hyponatremia and dehydration
• How does excessive secretion of antidiuretic hormone affect sodium levels?

  It leads to hyponatremia and overhydration
• What are the consequences of rapid changes in plasma sodium concentration?

  They can cause brain cell edema and neurological symptoms
• What neurological symptoms can arise from severe hyponatremia?

  Headache, nausea, lethargy, disorientation
• What plasma sodium concentration can lead to seizures and coma?

  Below 115 to 120 mmol/L
• Why can rapid correction of hyponatremia be dangerous?

  It may lead to osmotic injury of neurons
• What is the recommended rate of correction for chronic hyponatremia?

  Less than 10 to 12 mmol/L in 24 hours
• What is the most common electrolyte disorder in clinical practice?

  Hyponatremia
• What are the causes of hypernatremia?

  • Loss of water from extracellular fluid
  • Excess sodium in extracellular fluid
  • Inability to secrete antidiuretic hormone
  • Simple dehydration from inadequate water intake
• What can cause hypernatremia due to water loss?

  Inability to secrete antidiuretic hormone
• What is central diabetes insipidus?

  A disorder causing large amounts of dilute urine
• What is a common cause of hypernatremia during exercise?

  Water intake less than water loss
• How can hypernatremia be corrected?

  By administering hypo-osmotic sodium chloride solutions
• What should be considered when correcting hypernatremia?

  Correct slowly in chronic cases
• What mechanisms protect cells from hypernatremia?

  Increase intracellular concentration of sodium and solutes