Hypervolemic hypernatremia
Absolute excess of sodium in a blood very rich in water: it is the least common form of hypernatremia, a typical consequence of an increased iatrogenic or alimentary introduction of sodium, or of its retention in the kidney.
Possible causes:
- infusion of hypertonic solutions of NaCl (sodium chloride) and NaHCO 3 (sodium bicarbonate);
- increased sodium intake without adequate proportional intake of water (ingestion of sodium chloride per os kitchen salt, intake of emetics rich in sodium chloride, ingestion of sea water, artificial enteral and parenteral nutrition with hypertonic preparations, saline clisms hypertonic, intrauterine injections of hypertonic saline preparations, intake of inadequately diluted artificial milk, etc.);
- hypertonic dialysis (accidental modification of dialysate);
- prolonged corticosteroid therapy → corticosteroids increase sodium retention;
- primitive hyperaldosteronism (Conn's disease → pathology of the adrenal glands characterized by an excessive production of the hormone aldosterone, which increases sodium reabsorption in the kidney, favoring the elimination of potassium);
- hyperadrenocorticism (Cushing's syndrome) → cortisol reduces intestinal sodium losses.
Excess blood (hypervolemia) is associated with hypertension, which favors the escape of water and sodium from the vessel lumen → increase of water and sodium in the extracellular compartment with the appearance of the typical symptoms of hypervolemia: edema and hypertension.
Normovolemic or euvolemic hypernatriemia
Relative excess of sodium in a normal or slightly reduced blood volume: this is the typical consequence of a lack of water intake or water loss without a change in total body sodium. In such conditions there is a displacement of water from the intracellular compartment to the extracellular compartment, which tends to keep the volume around normal or slightly lower than normal (over time it tends to establish hypervolemic hypernatremia). Most conditions of normovolemic hypernatremia occur in Pediatrics and in Geriatrics, where water supply often depends on others.
Among the main causes of normovolemic hypernatriemia we recall:
- diabetes insipidus: excessive excretion of water at the kidney level due to inadequate production of vasopressin by neurohypophysis (neurogenic diabetes) and / or reduced sensitivity to its action (nephrogenic diabetes); vasopressin is a hormone that acts at the kidney level by stimulating water reabsorption and opposing diuresis
- iatrogenic causes
- hypodipsia / adipsia (reduction or absence of thirst with insufficient water intake)
- water shortage, inability to get water
Water leaks can be extrarenal (skin, respiratory tract) and in this case the urine will be particularly concentrated (high urinary osmolarity), or kidney and in this case the urine will be diluted (reduced urinary osmolarity). In any case, the presence of edema is not recorded in normovolemic hypernatriemias.
Hypovolemic hypernatremia
Relative excess of sodium in a reduced blood volume: it is the typical consequence of a marked dehydration with loss of hypotonic fluids (eg vomiting, sweat, diarrhea), such that the depletion of water exceeds that of sodium in percentages. As a result the aqueous component of the blood is reduced and the blood sodium is concentrated.
Among the main causes of hypovolemic hypernatremia we recall:
- vomiting, watery diarrhea
- adipsia / ipodipsia
- temperature
- extreme hypersudation and hyperventilation
- chronic nasal discharge
- urinary obstruction
- glycosuria from hyperglycemia
- diuretics
- osmotic diuresis (hyperglycemia, urea, mannitol)
- IRA, IRC
- loss of fluids in the third space
- burns
The reduction in blood volume (hypovolemia) is associated with symptoms such as orthostatic hypotension, reduced swelling of the skin, dry mucous membranes, collapsed neck veins and tachycardia. DEHYDRATION → IPERTONICITY OF EXTRACELLULAR FLUID → INTRACELLULAR DEHYDRATION (water moves from intracellular to extracellular spaces)
The joint evaluation of natriuria (concentration of sodium in the urine) can help establish whether the losses are primarily renal or extra-renal:
HYPERTOLEMIC FORMS
- natriuria> 20 mmol / L, with increased osmolality and specific gravity of urine, and polyuria
HYPOVOLEMIC FORMS
- natriuria> 20 mmol / L: increased renal losses of hypotonic liquids, accompanied by polyuria
- natriuria <20 mmol / L: increased fluid leakage via the extrarenal route (gastroenterological and / or cutaneous or respiratory) accompanied by oliguria or anuria
EUVOLEMIC FORMS
- natriuria <20 mmol / L: accompanied by marked polyuria with reduced osmolarity of urine and specific weight → Renal Loss, Diabetes insipidus
- natriuria> 20 mmol / L: hypodipsia, accompanied with oliguria or anuria with osmolarity and high urine specific gravity → Extrarenal losses
