Hyponatremia

Key points

Definition of hyponatremia

Blood sodium concentration <135 mmol / L

Classification and causes of hyponatremia

1. Hypertonic hyponatremia: caused by hyperglycemia
2. Isotonic hyponatremia or pseudohyponatremia: caused by an exaggerated increase in lipids and / or plasma proteins
3. Hypotonic hyponatremia: caused by the increase in the hormone ADH → water retention → hyponatremia

• Hypervolemic hyponatremia: caused by congestive heart failure, liver failure, cirrhosis, kidney disease
• Euvolemic hyponatremia: caused by inappropriate hypersecretion syndrome of the antidiuretic hormone (SIADH), hypothyroidism, adrenal insufficiency, polydipsia
• Hyponatremia hypovolemia: caused by taking diuretics, renal loss of salts, mineralocorticoid deficiency, diarrhea, vomiting, severe burns, pancreatitis, trauma

Symptoms of hyponatremia

Hallucinations, Ascites, Convulsions, Muscle Cramps, Epilepsy, Hypotension, Headache, Loss of Consciousness, Dry Mouth, Intense Thirst, Severe Drowsiness, Tachycardia

Therapies for hyponatremia

• Water restriction
• Hypertonic saline solutions intravenously
• Hormone therapy (for Addison's disease-dependent forms)
• tolvaptan
• Demeclocicline or lithium

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Definition of hyponatremia

We speak of hyponatremia - or hyponatremia - when the concentration of sodium in the blood (sodium) is abnormally low (<135mmol / L). In other words, hyponatremia is a metabolic condition in which serum sodium levels do not meet the body's needs.

As we know, sodium is a very important electrolyte, also useful for regulating the amount of intra / extra cellular water.

To understand...

Sodium is the main electrolyte of the extracellular fluid: 90% of the total body sodium is contained in the extracellular compartment, thanks to the action of the enzyme Na + - K + ATPase (which actively transports the sodium outside the cell).

Sodium is an important regulator of the osmolarity of plasma and extracellular fluid. When the sodium concentration falls below the normal range (deficit → hyponatremia) there is a more or less significant reduction in the volume of blood and interstitial fluid. Conversely, at high concentrations, sodium recalls large quantities of water by osmosis, laying the foundations for creating edema and hypertension.

Furthermore, sodium is involved in the transmission of nerve impulses, in cellular exchange and in muscle contraction: according to this, we understand how a condition of hyponatremia can upset all these functions to which the organism must fulfill.

Sodium sodium expresses the concentration of sodium in the blood, and is expressed in mmol / L

Although the daily water intake is extremely variable, the serum concentration of sodium fluctuates in a very narrow range (135-145 mmol / L), thanks to the extraordinary capacity of the kidney to dilute or concentrate urine.

We speak of hyponatremia proper when the serum sodium concentration falls below the value of 135mmol / L. The finding of hyponatremia - very common in sports - can also accompany dysmetabolic diseases (diabetes, hyperglycemic coma etc.).

Causes

It is not always so immediate to go back to the pathophysiological mechanisms underlying the electrolyte imbalance. Generally speaking, hyponatremia is favored by a SODIUM LOSS or a severe WATER RETENTION.

The etiopathological factors most involved in hyponatremia are:

1. Taking excessive amounts of water
2. Extended burns
3. Liver cirrhosis *
4. Low sodium diet
5. Severe and prolonged diarrhea
6. Intense physical exercise for a long time → excessive sweating
7. Diuretic, antidepressant, anticancer drugs
8. Congestive heart failure *
9. hypothyroidism
10. Addison's disease
11. Renal disorders
12. Syndrome of inappropriate antidiuretic hormone secretion (SIADH): ↑↑ vasopressin (antidiuretic hormone) → ↓ emission, water conservation in the blood and increase in volume → dilution of electrolytes in the blood → ↓ sodium
13. Sweating
14. Drug addiction (especially from ecstasy)
15. Brain trauma and severe burns
16. He retched

* It is believed that hyponatremia is a predictor of death among patients with cirrhosis or congestive heart failure:

1. hyponatremia due to heart failure → ↓ cardiac output and ↓ blood pressure → ↑↑ secretion of "hypovolemic" hormones renin, ADH, aldosterone → retention of water and sodium in the kidney, increase in volume with dilution of sodium and inability to eliminate l water taken

2. hyponatriemia due to liver cirrhosis → ↓ protein synthesis → reduction of the oncotic blood pressure → appearance of edema and hypovolemia → ↑↑ secretion of "hypovolemic" hormones renin, ADH, aldosterone → water and sodium retention in the kidney, increase in volume with dilution of sodium and inability to eliminate the water taken

Although it is still essential to weigh the intake of excessively salty foods, it is clear that the complete removal of salt from the diet is not a very sensible and intelligent attitude. Just think of the risks that an athlete can run following a similar behavior: the losses of salts during sport must be restored by taking isotonic drinks. Otherwise - for example by taking the famous "sodium-poor" waters after an intense physical effort - the risk of hyponatremia is raised, since the blood sodium already reduced by profuse sweating is further diluted.

Classification

After having listed the possible causes of hyponatremia, we distinguish three variants:

1. HYPER-OSMOLAR HYPONATRENE [osmolarity> 296 mOsm / kg H2O]: quite rare, it is essentially caused by the perfusion of hypertonic liquids, therefore too rich in solutes (eg mannitol, sorbitol, maltose, glucose or intravenous immunoglobulin infusion). Hyperosmolar hyponatraemia is often linked to hyperglycemia.
2. PSEUDOIPONATREMIA or ISOTONIC HYPONATRIEMIA [280-296 mOsm osmolarity / kg H2O]: the (apparent) reduction of sodium is a consequence of an exaggerated increase of lipids and / or plasma proteins
3. HYPO-OSMOLAR HYPONATREMIA [osmolarity <280 mOsm / kg H2O]: it is an expression of the kidney's inability to eliminate a sufficient amount of free water compared to the one assumed.

• Hypotonic or hypovolemic dehydration → hyponatremia associated with DEPLEION (reduction) VOLEMIC. Clinical condition caused by diuretic intake, Sali renal loss, mineralocorticoid deficiency (sodiuria> 20 mmol / L) or diarrhea, vomiting, severe burns, pancreatitis, trauma (sodiuria <20 mmol / L)
• Hypotonic hyperhydration or dilution hyponatremia or hypervolemic hyponatremia → hyponatremia WITH EDEMA: cirrhosis, nephrotic syndrome, cardiac / renal insufficiency
• Isovolemic or euvolemic hyponatremia: absence of edema and volume depletion. Characteristic condition of water intoxication, hypothyroidism, SIADH, glucocorticoid deficiency and primitive polydipsia (intense thirst)

In the next article, the symptoms, diagnostic strategies and therapies currently available for the treatment of hyponatremia are analyzed.