Question

68-year-old man with chronic renal failure was in the hospital in serious condition

recovering from a heart attack. He received fluid through an intravenous (IV) line. Late

one night, a weary nurse changed 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 starting 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

K+ 4.7 mEq / liter

C1- 101 mEq / liter

A chest x-ray revealed interstitial edema in the lungs.

Questions:

1a. Will the nurse's mistake increase or decrease the "saltiness" of the interstitial fluid?

1b. Given your knowledge of osmosis, will this cause the cells in the body to increase or

decrease in size? Explain your answer.

2. Why does this patient have pitting edema and inspiratory rales?

3. How would this increase in salt load affect the patient's blood-aldosterone level?

Why?

4. What other ways does the body have to control salt and water balance? How might they react in this situation?

Answer 1

1a. The nurse's mistake increases the saltiness of the interstitial fluid which then draws fluid from the cells (intracellular fluid) and leads to increased extracellular fluid overload and leads to edema.

1b. When the intracellular fluid is being transferred to the extracellular space the cell size will decrease and the cells shrink and become smaller

2. Increase in the extracellular fluid causes the fluid to accumulate in the interstitial spaces in the limbs causing edema and also in the lungs the fluid accumulates leading to pulmonary edema which causes inspiratory rales

3. As in this case the salt load in the body in already at higher levels, so it inhibits the renin angiotensin system which leads to decreased levels of aldosterone in the body

4. The main ways the body controls the salt and water balance are by

A. Renin angiotensin aldosterone system

B. Atrial and brain natriuretic peptides released by atria and ventricles

C. Thirst center in the hypothalamus also controls salt and water balance

They all can react in this case and finally leads to increased sodium and water loss through the kidneys and try to resolve the edema and rales