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If the level of sodium is decreases in our body, what is the symptom we can see in the patient? And what is the inner symptom or what is the inner physiology changes in human body? Okay.

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hyponatremia symptoms physiology cerebral edema authoritative patient information

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A decreased blood sodium level is called hyponatremia. It is usually defined as serum sodium below 135 mmol/L (mEq/L). The danger depends more on how quickly it falls than on the number alone.

Symptoms seen in a patient

Mild or gradual decrease
  • Often no obvious symptoms
  • Nausea, poor appetite, vomiting
  • Headache
  • Tiredness, weakness, lethargy
  • Muscle cramps or unsteadiness
  • Dizziness, poor balance, falls
  • Difficulty concentrating, irritability, confusion
Severe or rapidly developing decrease
  • Marked confusion, drowsiness, altered behavior
  • Disorientation or delirium
  • Muscle twitching
  • Seizures
  • Reduced consciousness, coma
  • Breathing may become slow or stop in extreme cases
Neurological symptoms such as seizures or decreased consciousness are a medical emergency. Mayo Clinic’s emergency warning signs include nausea/vomiting with confusion, seizures, or loss of consciousness.

What happens inside the body

Sodium is the main electrolyte in the fluid outside cells. It helps control extracellular fluid volume, blood pressure, nerve impulses, and water distribution between cells and blood.
In most cases, hyponatremia means there is too much water relative to sodium, not necessarily that the body has lost a large total amount of sodium.

Core physiology

  1. Blood becomes hypotonic
    • Low sodium lowers the osmolality, or concentration, of blood plasma.
  2. Water moves into cells by osmosis
    • Water shifts from the less concentrated blood into relatively more concentrated cells.
  3. Cells swell
    • Cell swelling can occur throughout the body, but the brain is most vulnerable because it sits inside the fixed space of the skull.
  4. Brain swelling causes symptoms
    • Swollen brain cells cause cerebral edema, raised intracranial pressure, and disturbed brain function.
    • This produces headache, nausea, confusion, seizures, coma, and in very severe acute cases, brainstem compression and respiratory arrest.
In acute hyponatremia, water enters brain cells, especially astrocytes, because the brain has not yet adapted to the low blood osmolality. This is why symptoms can be severe even at sodium values above 120 mmol/L if the fall was rapid. In chronic hyponatremia, brain cells partly adapt by losing electrolytes and other osmoles, so symptoms may be less obvious initially. Symptom to Diagnosis: An Evidence-Based Guide, Fourth Edition, pp. 6091-6093. The same adaptation is described in Comprehensive Clinical Nephrology, 7th Edition, pp. 739-752.

Why sodium becomes low

Common mechanisms include:
  • Too much water intake or intravenous hypotonic fluids
  • Increased ADH/vasopressin, which makes the kidneys retain water
  • Vomiting, diarrhea, sweating, burns, or use of diuretics
  • Heart failure, liver cirrhosis, or kidney disease
  • SIADH, a condition of inappropriate ADH secretion
  • Adrenal insufficiency or severe hypothyroidism
  • Certain medicines, especially thiazide diuretics, some antidepressants, antiseizure medicines, and others
ADH normally helps the kidney conserve water during dehydration. When ADH stays high inappropriately, the kidney continues retaining water, diluting sodium in the blood. Symptom to Diagnosis: An Evidence-Based Guide, Fourth Edition, pp. 6100-6108.

Important safety point

A low sodium level should not be self-treated by taking salt tablets or drinking less or more water without medical advice. Treatment depends on the cause and whether the person is dehydrated, fluid-overloaded, or has inappropriate water retention. Also, correcting chronic hyponatremia too quickly can seriously injure the brain.
If a patient has confusion, seizure, fainting, persistent vomiting, severe headache, or reduced consciousness, seek emergency care now.
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