HISTORY. Inquire about the patient's daily fluid and salt intake. Patients with hypernatremia often report a decrease in fluid intake and possibly a high salt intake. Since polyuria moving to oliguria is an early sign of hypernatremia, ask about daily urine output and if the urine appears concentrated. Question the patient about fever, diarrhea, and vomiting, which might contribute to dehydration. If hypernatremia is severe, the patient may be confused. Ask the family if the

456 Hypernatremia patient has been lethargic, disoriented, or agitated. These changes in mental status, along with occurrence of a seizure, indicate severe hypernatremia.

PHYSICAL EXAMINATION. Assess the patient's vital signs; fever, tachycardia, decreased blood pressure, and orthostatic hypotension are characteristic of hypernatremia. Assess the skin and mucous membranes for signs of dehydration. With pronounced hypernatremia, expect poor skin turgor; flushed skin color; dry mucous membranes; and a rough, dry tongue. With more severe hypernatremia, assess the patient for muscle twitching, hyperreflexia, tremors, seizures, and rigid paralysis.

PSYCHOSOCIAL. Assess the patient's ability to obtain adequate fluid intake. The patient's lethargic state contributes to the poor fluid intake. Assess the quality and support of the caregivers regarding their ability to provide for the patient's fluid intake. Since in severe hypernatremia, the symptoms are primarily neurological, assess the patient's level of orientation and her or his ability to communicate needs. Assess the safety needs of the patient, especially for the disoriented elderly or debilitated patient. Note that central nervous system symptoms are particularly upsetting for the patient and family and may create anxiety over the patient's long-term prognosis.

Diagnostic Highlights


Normal Result

Abnormality with Condition


Serum sodium

136-145 mEq/L

>145 mEq/L

Imbalance between sodium and water lead to excess sodium

Blood urea nitrogen (BUN)

5-20 mg/dL

May be elevated

Conditions that lead to dehydration and fluid loss may elevate BUN because of decreased renal blood flow and abnormal absorption of urea back into the blood

Serum chloride

95-108 mEq/L

>108 mEq/L

Reflects an excess of chloride

Serum osmolarity

280-295 mOsm/L

>295 mOsm/L

Water loss in the urine and hypernatremia lead to hemoconcentration; levels above 320 mOsm/L are considered "panic levels" and require immediate intervention

Urine osmolality

200-1200 mOsm/L

Varies depending on cause; often >800 mOsm/L

Used to diagnose nature of hypernatremia; osmolality refers to a solution's concentration of solute particles per kilogram of solvent; usual renal response to hypernatremia is excretion of maximally concentrated urine (<500 mL/day) with an osmolarity >800 mOsm/L

Other Tests: Complete blood count, urine sodium, serum glucose and protein level, urine specific gravity

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