A 70-year-old man comes to the office for follow-up of hypertension. He has been taking amlodipine but his recent home blood pressure readings have been elevated. The patient has a long smoking history and, despite many attempts at quitting, continues to smoke cigarettes. Blood pressure is 140/90 mm Hg and pulse is 76/min. Examination shows a bruit on auscultation of the abdomen. Further evaluation reveals bilateral renal artery stenosis. After initial discussion, the patient is started on daily lisinopril therapy. The patient is advised to return to the clinic in a few days. The close follow-up is recommended due to which of the following anticipated effects in this patient's kidney function?
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This patient has bilateral renal artery stenosis (RAS) and is at risk for acute renal failure with the initiation of an ACE inhibitor. Bilateral RAS, which typically occurs in older patients with widespread atherosclerosis, results in a reduction of renal perfusion. This leads to a lowered glomerular filtration rate (GFR) and activation of the renin-angiotensin-aldosterone system. Angiotensin II, a potent vasoconstrictor, increases systemic pressure and preferentially constricts the efferent arteriole, which increases intraglomerular hydrostatic pressure to maintain adequate GFR. The filtration fraction (FF)—the ratio of GFR to renal plasma flow (RPF) (FF = GFR/RPF)—is increased as the GFR remains relatively preserved despite the decreased RPF.
ACE inhibitors (eg, lisinopril) lower angiotensin II levels, causing a reduction in systemic pressures and relative dilation of the efferent arteriole. In patients with bilateral RAS, the reduced systemic pressures are no longer high enough to overcome the stenosis, and renal blood flow drops. The dilation of the efferent arteriole leads to a reduction of intraglomerular filtration pressure, which results in the reduction of GFR and filtration fraction.
Although patients with bilateral RAS treated with ACE inhibitors are at risk for acute renal failure, most patients can tolerate the medication with only a mild (<30%) rise in serum creatinine. In addition, risk can be reduced with discontinuation of diuretics, as volume depletion increases the dependence on efferent arteriolar constriction to maintain GFR.
Educational objective:
Patients with bilateral renal artery stenosis have reduced renal perfusion (due to atherosclerotic blockage) and are dependent upon angiotensin II-induced efferent vasoconstriction to maintain glomerular filtration rate. ACE inhibitors block angiotensin II-mediated vasoconstriction, which can reduce systemic blood pressure and lower renal perfusion. In addition, ACE inhibitors cause dilation of the efferent arteriole, leading to a reduction in glomerular filtration rate and renal filtration fraction.