Lecture on Renal Artery Stenosis and Doppler Ultrasound Criteria

Key Concepts

Criteria for Renal Artery Stenosis

• 180 cm/s Velocity Threshold:
  • Use color Doppler to identify turbulence in the main renal arterial segment.
  • Apply spectral Doppler to measure velocities.
  • Velocities ≥ 180 cm/s indicate stenosis.

Renal-to-Aortic Ratio (RAR)

• Necessity of RAR:

  • Peripheral arteries (e.g., carotid) use proximal to stenotic area PSV comparison.
  • Renal arteries, especially in elderly patients, often show stenosis at the origin, lacking a proximal segment for comparison.
  • Hence, the ratio of renal artery PSV to aortic PSV at the stenotic segment is used.

• Special Cases:

  • In elderly patients with heart disease, cardiac output may be low.
  • Aortic PSV may be around 35-40 cm/s.
  • Renal artery PSV at stenosis might be 140 cm/s (3.5 times aortic PSV).
  • Even if it doesn't meet the 180 cm/s criteria, a RAR of 3.5 still indicates stenosis.

Important Points

• Always consider RAR when diagnosing renal artery stenosis in patients with low cardiac output.
• A renal artery PSV that is 3.5 times the aortic PSV can diagnose stenosis even if it doesn't meet the absolute 180 cm/s criterion.