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HYPERNATREMIA, a serum sodium level greater than 145 mEq/L. The serum osmolality is not variable in this condition so, unlike hyponatremia, hypernatremia always indicates a hyperosmolar state. Symptoms include confusion, irritability, lethargy, neuromuscular excitability, seizures, tremors or coma. Hypernatremia generally results when losses of body water exceed sodium losses in conjunction with inadequate water replacement. Water loss may result from abnormal renal water conservation and/or extrarenal water losses, usually through the gastrointestinal system or skin.
There are three forms of hypernatremia based on volume status. Hypervolemic hypernatremia (characterized by the presence of edema) is usually iatrogenically induced when patients receive sodium bicarbonate solutions (there is approximately 1000 mEq/L of sodium in each 50 ml of sodium bicarbonate). Hypovolemic hypernatremia occurs when hypotonic solutions are lost through the kidney, skin or gastrointestinal and respiratory systems. Isovolemic hypernatremia is generally associated with diabetes insipidus.
Treatment depends on the underlying etiology. The initial goal when critical values are present is water replacement. This can be accomplished with oral rehydration in the conscious stable patient. In patients unable to tolerate oral fluids, intravenous infusion of fluids should be employed. Initially, isotonic saline should be used until the patient is hemodynamically stable. Once hypotension, azotemia and oliguria have corrected, fluid therapy may be changed to D5W or one half normal saline solutions. Hypervolemic hypernatremia is best treated by removing sodium in excess of water. This is done by inducing sodium and water loss via diuretic therapy and replacing the lost volume with water only. It is important to stress that the most complete treatment of hypernatremia is to determine the underlying etiology and correct the abnormality if possible.
The following calculations may be used to estimate the amount of volume replacement needed in an individual patient:
Current total body water = 0.6 x wt.(kg.)
Desired total body water = serum Na (mEq/L) x current total body water
normal serum Na (mEq/L)
