The nurse notes scattered crackles in both lungs and 1+ pitting edema when assessing a cardiac client. The physician is notified and orders furosemide (Lasix) 80 mg IV push stat. Which of the following diagnostic studies is monitored to assess for a major complication of this therapy?

Furosemide, a potassium-depleting diuretic, inhibits the reabsorption of sodium and chloride from the loop of Henle and the distal renal tubules. Serum electrolytes are monitored for hypokalemia. Severe acid-base imbalances influence the movement of potassium into and out of the cells, but arterial blood gases do not measure the serum potassium level. Furosemide is a potassium-depleting diuretic. A complete blood count does not reflect potassium levels. Abnormalities in potassium (both hyperkalemia and hypokalemia) are reflected in ECG changes, but these changes do not occur until the abnormality is severe.