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Chapter 3: Disorders of Water Balance: Hyponatremia and Hypernatremia

A 30-year-old woman competing in her first marathon is brought to the hospital after collapsing at the end of the race. She is confused and delirious and complains of a headache. Vital signs show blood pressure (BP) is 150/90 mm Hg, heart rate (HR) is 60 beats/min, and temperature is 37.4°C. Physical examination reveals no jugular venous distention, crackles at the lung bases, normal heart sounds, no organomegaly, a trace of pretibial edema, and no focal neurological findings.

Laboratory Data:

Serum Na 119, K 3.5, Cl 90, CO2 22 mmol/L

BUN 4, creatinine 0.5 mg/dL, glucose 80 mg/dL

Which ONE of the following is the BEST next step

A. Give 2 L of 0.9% saline by IV bolus.

B. Order urine osmolality and urine chemistries.

C. Give desmopressin.

D. Give intravenous furosemide.

E. Give 100 mL of 3% saline as a bolus.

The answer is E. The patient has acute hyponatremia with symptoms that reflect life-threatening cerebral edema. Unlike chronic hyponatremia, there is no risk of injury from rapid correction, so desmopressin is not indicated. Because hyponatremia may worsen as ingested water is absorbed, and because there is a risk of herniation, emergency therapy is needed without waiting for the results of laboratory tests. Transient SIADH is common in this setting and isotonic saline is contraindicated; it may lower the serum sodium concentration due to excretion of the infused sodium in a smaller volume of hypertonic urine, leading to net water retention. Although furosemide will partially block the excretion of concentrated urine, it will not reliably increase the serum sodium sufficiently. Hypertonic saline, best administered as a bolus is the most definitive way to raise the serum sodium concentration; the 100 mL bolus can be repeated up to two times if symptoms persist.

A 40-year-old man with a history of heavy beer drinking and hypertension treated with hydrochlorothiazide, is brought to the hospital after being found on the floor of his apartment. He is confused and delirious, fighting with caregivers. Vital signs show blood pressure is 95/60 mm Hg, heart rate is 100 beats/min, and temperature is 37.5°C. Physical examination reveals no jugular venous distention, scleral icterus, clear lungs, normal heart sounds, hepatomegaly, no edema, and no focal neurological signs.

Laboratory Data:

Serum Na 104, K 2.5, Cl 75, CO2 35 mmol/L

BUN 20, creatinine 1, glucose 70 mg/dL

He is given 2 L of 0.9% saline, 100 mg thiamine, and 40 mEq of KCl ...

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