Renal · Year 2 · from Renal
Case 2: Bilateral Renal Artery Stenosis with ACE Inhibitor-Induced AKI
Patient Presentation
A 68-year-old female with a history of peripheral vascular disease and coronary artery disease presents for follow-up after starting ramipril 2 weeks ago for newly diagnosed heart failure with reduced ejection fraction.
History of Present Illness
- Started ramipril 5 mg daily 14 days ago
- Routine labs today show markedly elevated creatinine
- No symptoms of uremia
- Mild dyspnea on exertion (unchanged from baseline)
- No edema reduction since starting medication
Physical Examination
- Blood pressure: 136/82 mmHg (improved from 168/98)
- Heart rate: 78 bpm
- Bilateral abdominal bruits
- 1+ bilateral pedal edema
- JVP 10 cm H2O
Workup
Laboratory Studies:
- Baseline creatinine (before ramipril): 1.3 mg/dL
- Current creatinine: 3.1 mg/dL (>100% increase)
- BUN: 58 mg/dL
- Potassium: 5.8 mEq/L
- Urine sodium: 12 mEq/L
- FENa: 0.6%
Imaging:
- Renal Doppler ultrasound: Bilateral renal artery stenosis (>70% bilaterally)
- Kidney sizes: Right 9.5 cm, Left 9.0 cm (mildly atrophic)
Diagnosis
ACE Inhibitor-Induced AKI due to Bilateral Renal Artery Stenosis
Discussion
This case demonstrates autoregulation and GFR maintenance:
- Autoregulation Limits: The lecture describes autoregulation over MAP 80-180 mmHg. In renal artery stenosis, the post-stenotic pressure is already reduced, and GFR depends heavily on angiotensin II-mediated efferent constriction.
- Efferent Arteriolar Constriction: Moderate efferent constriction increases PGC and maintains GFR despite reduced renal blood flow. ACE inhibitors remove this compensation.
- Filtration Fraction: Normally ~20%, in renal artery stenosis the filtration fraction increases as the kidney attempts to maintain GFR with reduced RBF. ACE inhibitors lower filtration fraction but at the cost of reduced GFR.
Treatment
- Discontinue ramipril immediately
- Creatinine expected to improve (a >30% rise mandates stopping the drug)
- Alternative heart failure management with hydralazine/nitrates
- Cardiology and vascular surgery consultation for consideration of renal artery revascularization
- In selected patients with bilateral stenosis and flash pulmonary edema, revascularization may be considered
Clinical Pearl
A creatinine rise >30% after ACE inhibitor or ARB initiation should prompt evaluation for bilateral renal artery stenosis or stenosis of a solitary kidney. However, a rise up to 30% is acceptable and reflects reduced intraglomerular pressure.