Treatment of hyperosmolar states

The therapeutic goal in hypernatremia is reduction of plasma osmolality towards normal by the administration of an excess of free water. Removal of solute is necessary only after inadvertant administration of NaCl; it is not usually a part of therapy and is accomplished by dialysis or diuretic administration. When free-water administration is planned, the major therapeutic questions are the type of fluid to be given and its rate of administration. Most agree that patients with hypernatremic dehydration should be treated with fluid which provides free water in excess of electrolytes. Fluid therapy is usually calculated to be administered over about 48 h

(Snyder,,et al,, 1987). Despite such recommendations, few human or experimental animal data are available for the ideal rate of fluid administration ( A.y,US,„,e.t,,a,l:, 1996).

The pathophysiology of cerebral edema complicating rapid correction of experimental hypernatremia in rabbits has recently been described ( AyUS„,,§í,§l: 1996), highlighting the dangers of overly rapid correction (less than 24 h) of hypernatremia. In adults with hypernatremia, 280 mmol/l glucose in water (5 per cent dextrose in water) has commonly been administered, but recent information suggests that therapy of hypernatremia with glucose-containing solutions (280 mmol/l glucose in water) may lead to cerebral intracellular lactic acidosis with increased mortality. Based on current knowledge, recommendations for treatment of chronic hypernatremia in adults are as follows.

1. If there is evidence of circulatory collapse, the patient should receive initial resuscitation with colloid which is sufficiently rapid to correct shock and stabilize the circulation.

2. Fluid deficit should be estimated on the basis of serum sodium and estimated total body water. The deficit should be given over a 48-h period, aiming for a decrement in serum osmolality of approximately 1 to 2 mOsm/kg/h. Maintenance fluids, which include replacement of urine volume with hypotonic fluid, are given in addition to the deficit.

3. Hypotonic fluid should be administered. The usual replacement fluid will be 77 mmol/l NaCl, and solutions containing glucose should be avoided if possible.

4. Plasma electrolytes should be monitored at frequent intervals, usually every 2 to 4 h. Many adult patients with hypernatremia have serious underlying systemic illness, and many such patients appear to die from their underlying illness rather than from hypernatremia. Close attention should be given to the treatment of associated medical conditions.

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