Home Forums Other Specialities Endocrinology HYPONATREMIA

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    Hyponatremia refers to the condition when blood levels of sodium (natrium) become low (hypo). Sodium is one of the most important electrolytes in the body that helps to maintain salt and water balance and therefore the blood volume. Therefore any alteration in sodium levels could have potentially serious consequences.

    Normally, should the sodium levels (and blood volume) go down, regulatory mechanisms (sensors) in the kidneys, blood vessels and heart detect these changes and appropriate corrective measures will be initiated. As a result the kidneys will excrete less sodium thereby restoring sodium levels and blood volume. When these mechanisms fail hyponatremia results. It can be acute or chronic.

    Causes of hyponatremia
    • Severe vomiting and diarrhea resulting in loss of sodium and other electrolytes as well
    • Disease conditions that cause body to retain fluid – eg kidney failure, liver failure, heart failure (often more fluid is retained relative to salt or sodium causing the sodium to become diluted) with resultant hyponatremia
    • Severe burns
    • Addison disease – impaired aldosterone (hormone necessary for sodium reabsorption by kidneys) secretion by adrenal glands
    • Thiazide diuretics – increased sodium and water excretion by the kidneys
    • Excessive water drinking – psychogenic polydipsia, long distance runners who drink too much water
    • Excess secretion of vasopressin (antidiuretic hormone- ADH) with resultant water retention by kidneys – eg drugs (such as analgesics, antidepressants, chlorpropamide, Ecstasy drug), SIADH (syndrome of inappropriate ADH secretion) in certain infections, brain diseases and cancers

    Types of hyponatremia
    Since salt and water balance are closely related, sodium measurements must be taken into
    consideration with blood volume measurements. The types of hyponatremia include the following

    Hypovolemic hyponatremia (associated with low blood volume)
    Hypervolemic hyponatremia (associated with high blood volume)
    Euvolemic hyponatremia (associated with normal blood volume)

    Usually the underlying cause in the case of hypovolemic and hypervolemic hyponatremia will be obvious. Euvolemic patients should be investigated further for underlying endocrine abnormalities such as Addison disease, hypothyroidism or SIADH

    Persons at risk of hyponatremia
    • Older adults
    • Premenopausal women
    • Long distance and endurance athletes

    Clinical features of hyponatremia
    The brain cells are particularly sensitive to changes in sodium concentration and symptoms of brain dysfunction dominate the clinical picture. These include the following

    • Headache
    • Nausea and vomiting
    • Irritability and restlessness
    • Confusion
    • Tiredness and fatigue
    • Muscle weakness, spasms or cramps
    • Seizures
    • Coma

    Complications of hyponatremia
    When sodium levels drop suddenly, without enough time for compensatory mechanisms to reverse this, rapid brain swelling occurs with loss of consciousness and death.

    Diagnosis of hyponatremia
    Following a detailed history and thorough physical examination, if there is a suspicion of sodium
    depletion, the diagnosis may be confirmed by

    • Serum and urine sodium measurements (in hyponatremia serum sodium falls below 136 mEq/L)
    • Serum and urine osmolality
    • Assessment of blood volume of patient clinically

    Treatment of hyponatremia
    Treatment of hyponatremia aims at addressing the underlying cause

    • Stopping any drugs or adjusting the dose of drugs known to cause hyponatremia
    • Restriction of fluid intake to correct chronic, mild hyponatremia, only occasionally needing IV saline infusion over a few days to restore normal levels. Rapid correction of mild hyponatremia can cause brain damage
    • Rapid onset moderate to severe hyponatremia may require IV infusion of hypertonic saline over a few minutes to hours depending on severity. The patient should be closely monitored in the ICU with serum sodium levels measured two hourly. After sodium level has increased by the initial target of 4 to 6 mEq/L, the rate of infusion is slowed so that serum sodium level does not increase more than 8 mEq/L in the first 24 h.
    • Newer agents termed vaptans (vasopressin receptor antagonists) are sometimes needed in severe resistant hyponatremia. These have to be used with caution due to possible adverse effects
    • Symptomatic treatment of headache, vomiting seizures

    SIADH – In Brief
    The syndrome of inappropriate ADH ( vasopressin) secretion (SIADH) is caused by inappropriate and excessive vasopressin secretion from the posterior pituitary in the absence of stimulating causes such as kidney failure, heart failure, drugs, stress, thyroid dysfunction. Causes of SIADH include brain conditions such as meningitis, stroke, psychosis, certain cancers, protein energy malnutrition.

    It is diagnosed by low serum sodium osmolality with high urine osmolality (solute concentration). Treatment involves restriction of fluid intake and treating the underlying cause

    Prevention of hyponatremia
    • Drink water in moderation
    • Persons indulging in high intensity activities should drink sports beverages
    • Manage drugs known to cause hyponatremia appropriately
    • If you suffer from a condition that can cause hyponatremia, take precautions to prevent this from happening. Discuss with your doctor the various options available

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