Hyponatremia

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Hyponatremia

• Kelly Lindblom

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Hyponatremia

• Common electrolyte abnormality
• Isolation
• Complication of other illnesses
• Serum Na lt 135 mEq/L
• Severe if lt 120 mEq/L
• Common in the very young and the very old
• 2.5 of hospitalized patients

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Normal Lab Values

• Normal Serum Na 135-145mEq/Liter
• Normal urine Na 10-20 mEq/Liter
• Normal Serum Osmolarity 280-300 mOsm/L
• Normal Urine Osmolarity 500-800mOsm/kg

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Water Sodium

• Sodium and Water homeostasis are linked
• A change in water intake/output results in a
  change in sodium
• Sodium concentration is affected by changes in
  water and sodium
• Clinical effects due to movement of water in and
  out of cells

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Water

• Total body water
• Lower in obese people and elderly
• 2/3 of TBW is intracellular
• 1/3 of TBW is extracellular
• ¾ of ECF is interstitial space
• ¼ is intravascular
• Daily intake of 700-800ml needed to match total
  water loss
• Expired air
• Skin evaporation

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Two Major Principles

• Water moves rapidly across cell membranes
  osmolarities of intracellular and extracellular
  fluids remain almost exactly equal to each other
  except for a few minutes after a change in one of
  the compartments.
• Cell membranes are almost completely impermeable
  to many solutes
• therefore, the number of osmoles in the
  extracellular or intracellular fluid generally
  remains constant unless solutes are added to or
  lost from the extracellular compartment.

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ICF ECF Composition
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Osmolality
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Osmosis
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Physiological Affects

• Low Sodium
• Shift of Water from ECF to ICF
• Water enters brain cells
• Cerebral Edema

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Sodium - Clinical Effects

• Hyponatraemia - water drawn into cells
• lt130 nausea, drowsiness
• lt120 vomiting, confusion
• lt110 convulsions, coma
• Depends on rate of change
• Chronic vs Acute
• Rate of correction differs in acute vs chronic

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Abnormal Sodium Regulation

• Thirst disturbance
• Anti-diuretic Hormone
• Renin-angiotensin-aldosterone system
• Natriuretic Peptides

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Anti-diuretic Hormone(Arginine Vasopressin)

• Hormone produced in hypothalamus
• Released by pituitary gland
• Action
• Urine output
• Water absorption

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Aldosterone

• Synthesized by adrenal cortex, regulated by the
  renin-angiotensin-aldosterone mechanism
• Released in response to hypovolemia
• Causes absorption of sodium at distal renal
  tubule
• Water follows sodium

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Natriuretic Peptides

• Secreted in response to stretching of myocardium
  and blood vessels
• Natriuresis
• Excretion of large amounts of sodium into urine
• Water follows sodium

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Causes of Hyponatremia

• Multiple Causes
• SIADH
• Hyperglycemia-induced
• Exercise-associated Hyponatremia
• Diabetes Insipidus
• Post-operative
• Potomania
• MDMA or ecstasy

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Diagnosing Treating Hyponatremia

• What is the plasma osmolality?
• What is the ECF volume?
• Clinical signs of
• Hypovolemic
• Hypervolemic
• Euvolemic

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Management of Hyponatremia

• Ask the following questions
• Do we know the cause, can it be corrected?
• Is it chronic or acute hyponatremia?
• What is the volume status of the patient?
• What is the appropriate fluid replacement
  therapy?
• How quickly should the fluids be administered to
  avoid adverse consequences?