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ساعت ۱٠:٥٧ ‎ق.ظ روز ۱۳۸٩/٤/٢٠   کلمات کلیدی: electrolyte disturbances ،mental status

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Consider Electrolyte Disturbances When There is a Change of Mental Status

Nirav G. Shah MD

Toxic-metabolic encephalopathy results in a change of mental status and is a common diagnosis in the intensive care unit (ICU). Electrolyte disturbances need to be high on the list of differential diagnoses when evaluating the ICU patient with altered mental status. Some commonly encountered disturbances include hyponatremia, hypernatremia, hypoglycemia, hyperglycemia, hypermagnesia, acidosis, and alkalosis.

Watch Out For

Clinical manifestations of hyponatremia include dysfunction of the central nervous system and are dependent on the severity and rate of development. For instance, the acute development of hyponatremia (<24 hours) as well as extremely low sodium concentrations (<120 mEq/L) may manifest with severe symptoms including confusion, agitation, delirium, lethargy, and seizures. The most common etiologies include syndrome of inappropriate antidiuretic hormone (SIADH), treatment with thiazide diuretics, polydipsia, and inappropriate administration of hypotonic intravenous fluids. Treatment consists of free-water restriction and, in severe cases, administration of hypertonic saline to correct the hyponatremia. To prevent central pontine myelinolysis, care must be taken to prevent too rapid a rise in serum sodium. This disorder results in quadriplegia and pseudobulbar palsy and is preventable with the judicious correction of serum sodium. The goal in patients with chronic hyponatremia and in asymptomatic patients should be a gradual correction of <10 mEq/L per 24 hours.

Similarly, hypernatremia can result in altered mental status. The most common symptoms include generalized muscle weakness, lethargy, confusion, and coma. As with hyponatremia, symptoms are dependent on the degree and rate of rise of serum sodium. Etiologies contributing to this disorder include diabetes insipidus, loop diuretics, gastrointestinal losses, and hypertonic sodium. Treatment consists of treating the underlying illness and correcting the hypertonicity. The latter is achieved by administration of hypotonic saline to lower the serum sodium concentration by 1 mEq/L per hour in acute hypernatremia and 0.5 mEq/L per hour in chronic hypernatremia (goal reduction of 10 mEq/L per day in chronic cases). A relatively slow correction helps to prevent cerebral edema and seizures.

Hypo- and hyper-glycemia can also cause a state of altered mental status. In cases of hypoglycemia, symptoms may include confusion, tremulousness, coma, and seizures. The cause can be inappropriate insulin or oral hypoglycemic agent administration, insulinomas, liver failure, and infection. It is treated by administration of a dextrose load (usually one ampule of D50), which should result in resolution of clinical symptoms. Hyperglycemia can result in visual changes, lethargy, coma, and seizures and most commonly occurs as part of the clinical spectrum of diabetic ketoacidosis or nonketotic hyperglycemia. Treatment requires adequate fluid resuscitation, intravenous insulin therapy, correction of electrolyte derangements (particularly potassium), and treatment of the underlying cause.

The most common side effects of hypermagnesemia are the neurologic symptoms of obtundation, loss of deep tendon reflexes, and muscle paralysis. They are most frequently seen in patients with renal failure and women on high-dose magnesium infusions for eclampsia. In patients with compromised renal function, either hemodialysis or peritoneal dialysis must be initiated. In addition, when rapid reversal is required, calcium may be given intravenously as a magnesium antagonist. For women on magnesium infusions and with normal renal function, cessation usually results in a fairly rapid return to normal serum levels.

Finally, when assessing altered mentation the differential should always include hypoxia, acidosis and alkalosis. An arterial blood gas will indicate the degree of acidosis or alkalosis and can assist with determining whether its origin is respiratory, metabolic, or a mixed etiology. In the ICU setting, the most common etiologies are sepsis, uremia, hepatic failure, and electrolyte abnormalities. Treatment consists of correcting the underlying problem while providing supportive care for the acidosis or alkalosis.

 

Suggested Readings

Adrogué HJ, Madias NE. Hyponatremia. N Engl J Med. 2000;342:1581–1589.

Adrogué HJ, Madias NE. Primary care: hypernatremia. N Engl J Med. 2000;342:1493–1499.

Bolton CF, Young GB, eds. Baillere's Clinical Neurology. London: Balliere Tindall; 1996:577.