LOW SODIUM in the blood: causes, symptoms and treatment of hyponatremia or hyponatremia

Hyponatremia or hyponatremia

The feedback from low sodium in the blood it takes the scientific name of hyponatremia or hyponatremia. Sodium is a mineral salt, and is the main ion present in the bloodstream. The presence of a reduced sodemia could be caused From one reduced intake sodium or, more frequently, from a increased loss, renal or intestinal. There are also cases in which the real amount of sodium is normal, but this is diulito in a large amount of liquids, resulting in decreased: this is the case of people with water retention. THE symptoms of hyponatrimia range from malaise, to confusion, to lethargy and com. There therapy consists in the cautious administration of sodium until it returns to acceptable levels, removing the triggering cause of hyponatremia.

Low sodium values

We speak of low sodium when sodaemia is lower than 135 mmol / l or mEq / l (135 millimoles per liter or milliequivalents per liter).

What is sodium

Sodium is a mineral salt, and is the main one ion present in the bloodstream. The chemical symbol for sodium is Na. It is very important for the human body by regulating fundamental functions such as acid base balance, osmolarity of plasma and, above all, allowing the formation of gradients between cell membranes and thus allowing the transmission of nerve impulses.

Sodium is introduced with the diet and absorbed in the final part of the small intestine, the ileum. The daily dose of sodium introduced with the power supply it is around 1.5 g, according to the LARN - Reference levels of intake of the SINU (Stalian Society of Human Nutrition), allowing to maintain a total amount of body sodium between 90-100 g.

The kidney it represents the main regulator of sodium metabolism; in the balance between the various mineral salts in the blood, an important action is exercised byaldosterone, a hormone produced by the adrenal cortex that increases the reabsorption of sodium and, at the same time, promotes the elimination of potassium ions. Another very important substance is the vasopressin, also called antidiuretic hormone or ADH, produced by the hypothalamus and secreted at the level of the posterior pituitary, which promotes the reabsorption of water in the kidney thus allowing to retain fluids in the body: this hormone is activated in rpesenza of dehydration or arterial hypotension. Finally, the atrial natriuretic peptide, which acts in the opposite way, facilitating the excretion of sodium and water losses.

Causes of Hyposodemia

Sodium is eliminated from the body through the action of kidneys, ie via urine. In pathological conditions such as diarrhea, vomiting or burns skin, there may be a substantial loss of sodium, which is therefore defined extrarenal loss.

The main ones causes of hypontriemia they are therefore a reduced sodium intake with food, increased renal loss, the presence of intestinal or skin loss and dilution in patients with body fluid retention.

In the general population, the main cause of low sodium is therapy with diuretic drugs. It is good to remember that diuretic induced hyponatremia it is almost always due to thiazides (eg hydrochlorothiazide). Loop diuretics (e.g. furosemide or torasemide), also very common in patients with arterial hypertension, heart failure or liver cirrhosis, reduce the tone of the medullary interstitium and reduce the ability to maximize urinary concentration. This limits the ability of vasopressin (ADH) to stimulate water retention. Thiazide diuretics, on the other hand, cause both Na + and K 'loss and ADH-mediated water retention.

In general, hypoosmolar hyponatremia is due to a primary increase in water (and secondary loss of sodium from the body by renal elimination, in an attempt to eliminate fluids.
Hypoosmolar hyponatremia can also be linked to a primary loss of Na '(with secondary increase in water). Diuretic drugs are the main culprits of sodium loss, especially in older people.

The most frequent cause of normovolemic hyponatremia, or sodium deficiency in the circulation with normal blood volume, is SIADH, i.e. excessive secretion of vasopressin by the pituitary or other parts of the body (ectopic secretion). Vasopressin is a hormone that reduces the elimination of water, retaining fluids and liquids inside the body and "diluting" all the body's mineral salts, especially sodium. Apart from pituitary tumors, other causes of inappropriate ADH secretion are neuropsychiatric and lung diseases, malignant tumors, major surgery (postoperative pain) and drugs.

Other hormonal causes of low sodium are hypothyroidism (low levels of thyroid hormones) and adrenal insufficiency. Although mineralocorticoid deficiency (first of all aldosterone) can contribute to hyponatremia in the course of reduced adrenal function, cortisol deficiency is the real responsible for the reduction in sodium levels: low cortisol causes hypersecretion of vasopressin and indirectly (following volume depletion) or directly (by cosecretion the hormone stimulating the secretion of corticotropin).

Hypothyroidism, on the other hand, causes hyponatremia mainly due to a reduction in cardiac power, with a reduction in cardiac output and GFR and an increase in vasopressin secretion in response to haemodynamic stimuli.

Reduced levels of sodaemia can also be found in people who drink excessive amounts of fluids, such as alcoholics (especially beer drinkers, who can take several liters of fluids per day) or people with psychiatric problems, in a context that has been termed psychogenic polydipsia.

To distinguish a person with SIADH from a person with psychogenic polydispy, the thirst test

But what are the causes of low sodium? The main causes of hyponatremia are:

Hypoosmolar or hypotonic ponatremia (i.e. with reduced blood osmolarity)

  1. Primary sodium loss (secondary increase in water)
  • Skin discharges: sweating, burns
  • Gastrointestinal leaks: vomiting, diarrhea, presence of skin drains or fistulas
  • Kidney losses:
    • use of diuretics, in particular thiazides
    • osmotic diuresis
    • hypoaldosteronism
    • sodium-dispersing nephropathy
    • post-obstructive diuresis
    • acute non-oliguric tubular necrosis
  1. Primary increase in water (with secondary sodium loss)
  • Primary polydipsia (people who over-drink)
  • Reduced solute intake (e.g. excessive alcohol intake as in the case of beer potomania)
  • Secretion of ADH (vasopressin) due to stimuli such as pain, nausea, drugs
  • Syndrome of Inappropriate Antidiuretic Hormone ADH Secretion (SIADH)
  • Adrenal insufficiency with glucocorticoid deficiency
  • Hypothyroidism
  • Chronic renal failure

Hemodilution hyponatremia with normal total sodium (increased body fluids)

  • Heart failure
  • Cirrhosis of the liver
  • Nephrotic syndrome

Hyponatremia due to reduced sodium intake with diet and nutrition


  • Normal plasma osmolality (isotonic hyponatremia)
    • Increased circulating fats: hypercholesterolemia, hypertriglyceridemia or mixed hyperlipidemia
    • Total protein increased: hyperproteinemia
    • Recent transurethral resection of prostate / bladder cancer (cystoclysis or bladder irrigation with mannitol or sorbitol uptake)
  • increased plasma osmolality (hypertonic hyponatremia)
    • High blood glucose: hyperglycemia (Plasma sodium concentration decreases by 1.4 mmol / 1 for every 100 mg! Dl increase in plasma glucose concentration.)
    • Intravenous administration of mannitol.

Symptoms of Hyponatremia

Symptoms of hyponatremia are related to the osmotic displacement of water which causes an increase in volume
of intracellular fluids, especially swelling of brain cells, and consequently brain edema. The symptoms are therefore mostly neurological, and their severity and severity depends on the sodium levels in the blood and on how quickly the hyponatremia is established.

The main symptoms of low sodium are:

  • Nausea
  • Malaise
  • Headache (headache)
  • Drowsiness
  • Sensory clouding (confusional state)
  • State of stupor
  • Convulsions
  • Coma

These last 3 symptoms typically only occur when sodium values are below 120 mmol / L or if there has been a drop of more than 12-15 mmol / L in sodium within 24 hours or less.

Differential diagnosis of hyponatremia

The diagnosis of hyponatremia is in itself simple, but what is complex is to understand the cause. The underlying disease can often be diagnosed with a careful history and physical examination that includes an assessment of the presence or absence of water retention (increased extracellular body fluids) and actual circulating volume. For example, in diseases such as cirrhosis or right heart failure there will be an increase in total body fluids, with manifestations such as ascites or declining edema. Conversely, people on excessive diuretic therapy may appear dehydrated and hypotensive.

Low sodium or hyponatremia

Main causes of low sodium, distinguished by the amount of sodium present in the urine and urinary osmolarity.

Beyond the physical appearance and what emerges from the physical examination, blood and urine tests are the real parameters to understand where low sodium levels in the blood come from.

Fundamental exams are:

  • creatinine
  • urea
  • potassium
  • football
  • chlorine
  • total protein
  • albumin
  • blood count
  • plasma osmolarity
  • urinary osmolarity
  • urinary sodium (sodiuria)
  • urinary potassium (potassium)
  • urinary cortisol (cortisoluria)

For example, in a psychiatric patient who drinks an exaggerated amount of water every day, a urinary osmolarity of less than 100 milliosmol / kg and a specific gravity of less than 1.003 will be found in addition to hyponatremia. On the contrary, in the presence of severe hyperglycemia, sodium will be reduced but the urinary osmolarity will be very high, since the urine is full of glucose molecules.

Using the 24-hour urinary sodium instead, it is easy to understand how in case of protein-dispersing nephropathy, hypoaldosteronism or massive use of diuretic drugs, urinary sodium excretion will be increased (sodium greater than 20 mmol / l). Conversely, in people with a reduced sodium intake from the diet or in those who have lost sodium due to burns, the sodiuria will be less than 20 mmol / l, often with values close to zero.



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