فزونی سدیم (هایپرناترمی)

Striving for balance

The body strives to maintain a normal sodium level by secreting ADH from the posterior pituitary gland. This hormone causes water to be retained, which helps to lower serum sodium levels.

The cells also play a role in maintaining sodium balance. When serum osmolality increases because of hypernatremia, fluid moves by osmosis from inside the cell to outside the cell, to balance the concentrations in the two compartments.

As fluid leaves the cells, they become dehydrated and shrink especially those of the CNS. When this occurs, patients may show signs of neurologic impairment. They may also show signs of hypervolemia (fluid overload) from increased extracellular fluid volume in the blood vessels. If the overload is severe enough, subarachnoid hemorrhage may occur.

Increased concentration

A water deficit can cause hypernatremia that is, more sodium relative to water in the body. Excessive intake of sodium can also cause it. Regardless of the cause, body fluids become hypertonic (more concentrated).

 Water deficit

A water deficit can occur alone or with a sodium loss (but more water is lost than sodium). In either case, serum sodium levels are elevated. This elevation is more dangerous in debilitated patients and those with deficient water intake.

Insensible water losses of several liters per day can result from fever and heat stroke, with older adults and athletes being equally susceptible. Significant water losses also occur in patients with pulmonary infections, who lose water vapor from the lungs through hyperventilation, and in patients with extensive burns. Vomiting and severe, watery diarrhea are other causes of water loss and subsequent hypernatremia; either can be especially dangerous in children.

Thirst to an extreme

Patients with diabetes insipidus have extreme thirst and enormous urinary losses, in many cases more than 4 gal (15 L)/day. Usually, they can drink enough fluids to match the urinary losses; otherwise, severe dehydration and hypernatremia occur. Diabetes insipidus may result from a lack of ADH from the brain (central diabetes insipidus) or a lack of response from the kidneys to ADH (nephrogenic diabetes insipidus).

• Central diabetes insipidus may be caused by a tumor or head trauma (injury or surgery), or it may be idiopathic (no known cause). It responds well to vasopressin (another name for ADH).

• nephrogenic diabetes insipidus doesn’t respond well to vasopressin and is more likely to occur with an electrolyte imbalance such as hypokalemia or with certain medications such as lithium.

Excessive sodium intake

Like water losses from the body, sodium gains can cause hypernatremia. Several factors can contribute to a high sodium level, including salt tablets, high-sodium foods, and medications such as sodium polystyrene sulfonate (Kayexalate). Excessive parenteral administration of sodium solutions, such as hypertonic saline solutions or sodium bicarbonate preparations, and gastric or enteral tube feedings can also cause hypernatremia.

Other causes of increased sodium levels include inadvertent introduction of hypertonic saline solution into maternal circulation during therapeutic abortion and near drowning in salt water. Excessive amounts of adrenocortical hormones (as in Cushing’s syndrome and hyperaldosteronism) also affect water and sodium balance.

That flushed, fevered feeling

You may also observe a low-grade fever and flushed skin. The patient may complain of intense thirst from stimulation of the hypothalamus from increased osmolality.

Other signs and symptoms vary depending on the cause of the high sodium levels. If a sodium gain has occurred, fluid may be drawn into the blood vessels and the patient will appear hypervolemic, with an elevated blood pressure, bounding pulse, and dyspnea.

If water loss occurs, fluid leaves the blood vessels and you’ll notice signs of hypovolemia, such as :

• dry mucous membranes
• oliguria
• orthostatic hypotension (blood pressure drop and heart rate increase with position changes).