Why are ACE inhibitors contraindicated in bilateral renal artery stenosis and what monitoring is essential?

• A. ACE inhibitors can cause severe renal failure in bilateral renal artery stenosis; monitor creatinine and potassium.
• B. They improve renal function in bilateral RAS; monitor blood pressure.
• C. They are safe in all forms of kidney disease.
• D. They cause hyperkalemia but good kidney perfusion.

Answer: (A)

The key idea is that ACE inhibitors can dangerously reduce kidney function when both renal arteries are narrowed because the kidneys rely on angiotensin II to keep glomerular filtration pressure high. Blocking angiotensin II removes this efferent arteriolar constriction, lowering glomerular capillary pressure and GFR. In bilateral renal artery stenosis there isn’t a healthy downstream kidney to compensate, so this can precipitate acute kidney injury. The risk is compounded by the potential for hyperkalemia due to reduced aldosterone-mediated potassium excretion.

Because of this, the essential monitoring after starting or increasing an ACE inhibitor is measuring serum creatinine to detect a decline in kidney function and checking potassium levels to catch hyperkalemia. Baseline values should be obtained, with follow-up labs in the first one to two weeks (and sooner if symptoms appear), then periodically thereafter. Blood pressure should also be monitored, but the critical safety signals are the creatinine and potassium changes.