George, a 68-year-old man with chronic renal failure was in the hospital in serious condition recovering from a heart attack. He had just undergone "balloon angioplasty" to redilate his left coronary artery, and was thus on an "npo" diet (i.e. he was not allowed to have food or drink by mouth). He received fluid through an intravenous (IV) line. Late one night, a weary nurse who was on the 11th hour of a 12-hour shift came into the patient's room to replace the man's empty IV bag with a new one. Misreading the physician's orders, he hooked up a fresh bag of IV fluid that was "twice-normal" saline rather than "half-normal" saline (in other words, the patient started receiving a fluid that was four times saltier than it should have been). This mistake was not noticed until the following morning. At that time, the man had marked pitting edema around the sacral region and had inspiratory rales ("wet-sounding crackles") at the bases of the lungs on each side. He complained that it was difficult to breathe as well. Blood was drawn, revealing the following:

Na⁺

157 mEq / liter (Normal = 136-145 mEq / liter)

K⁺       

4.7 mEq / liter (Normal = 3.5-5.0 mEq / liter)

C1^-

101 mEq / liter (Normal = 96-106 mEq / liter)

5. Most dissolved substances in the blood plasma can easily move out of the bloodstream and into the interstitial fluid surrounding the cells. Will the nurse's mistake increase or decrease the "saltiness" of the interstitial fluid?

6. What symptoms might result from hypernatremia?

7. How would this increase in salt load affect the patient's blood-aldosterone level? In your answer, explain the function of the hormone aldosterone.