Which of the following statement(s) is/are true concerning abnormalities in serum sodium?

b. Hyponatremia can occur in situations of excessive solute

c. Most surgical patients with hyponatremia are best treated by free water restriction

d. Central nervous system effects are the predominant symptom of hypernatremia

The most common cause of hyponatremia is an excess of free water rather than a deficit of total body sodium. Hyponatremia is frequently seen in the postoperative or post-trauma patients because increased ADH secretion acts on the collecting tubules of the kidney to increase free water reabsorption. Although hyponatremia most often results from excess free water, it can occur in the presence of excess solute. In this situation, TBW content is either normal or diminished but the plasma osmolality is increased. An example of this hyperosmolar-hyponatremic state is untreated hyperglycemia. Excess solute may also be due to exogenous administration or ingestion of mannitol, ethanol, methanol, or ethylene glycol.

 Most surgical patients with hyponatremia are euvolemic or hypervolemic. Such patients, if asymptomatic, are best treated by free water restriction, since free water overload is the cause of the condition. Hypernatremia is a less common problem in surgical patients than hyponatremia and is usually the result of excess free water loss associated with hypovolemia. Hypernatremia may also be secondary to increased total body content of sodium, which is usually related to exogenous administration of sodium. The symptoms of hypernatremia are related to the hyperosmolar state. CNS effects predominate because of cellular dehydration as water passes into the extracellular space. Once hypernatremia becomes symptomatic, it is associated with significant morbidity and mortality. Prompt treatment of hypernatremia is essential. Rapid correction, however, of hypernatremia is associated with significant risk of cerebral edema and herniation. Because chronic hypernatremia is relatively well tolerated, there are few advantages to rapidly correcting the free water deficit. Moderate degrees of hypernatremia are tolerated well, and symptoms rarely develop unless serum sodium levels exceed 160 mEq/liter. The development of symptoms also depends on the rapidity at which hypernatremia develops.