Goals. Access flow and renal artery stenosis evaluation by Doppler ultrasound. Reimbursement. WHY use of Doppler Ultrasound

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1 Access flow and renal artery stenosis evaluation by Doppler ultrasound Adina Voiculescu, MD Interventional Nephrology Brigham and Women s Hospital Boston Instructor at Harvard Medical School Understand Goals Ultrasound and Doppler principles How to measure access flow volume with US Doppler ultrasound criteria for renal artery stenosis evaluation WHY use of Doppler Ultrasound Non invasive Non toxic Easy done But Is it reliable? Is it helpful? Is it reimbursable? Reimbursement Difficult cannulation Thrombus aspiration Venous pressures greater 200 mmhg on 300 ml/min pump Elevated recirculation 15% Low URR of less than 60% Access collapse suggesting poor arterial inflow Poor maturation Loss of thrill Distal limb ischemia Clinical signs of infection Perigraft mass, aneurysm, pseudo aneurysm Role of flow measurment with ultrasound for access evaluation Low flow *** High flow *** PRE ESRD *** Performing the exam Patient lying supine Arm rotated externally Begin with evaluation of artery in transverse view Scan entire access in this view Longitudinal scan of artery Doppler of artery, anastomosis and access vein while documenting waveforms Measure flow volume

2 The right probe? Sector scanner Convex probe Linear probe 1 5 MHz 2 5 MHz 7 16 MHz Basics of ultrasound Sound is a mechanical wave, which requires a medium to travel in The frequency of the wave is measured in cycles per second or Hertz (1/s = 1 Hz) Typical frequency for US for medical purposes 2 15 MHz The source of the ultrasound wave is the piezoelectric crystal located in the transducer Returning echoes are converted into images on the ultrasound monitor Structures are depicted in black and white and gray shades (B Mode) Role of B Mode Ultrasound for access evaluation Prinicples of Doppler Dopplereffect (C.J. Doppler 1842): Determine depth of access vein *** Determine volume of thrombus *** Determine fluid collections *** Determiniation of stenosis??? * Prinicples of Doppler Prinicples of Doppler V = F x C 2 F 0 x cos α V = Blood flow velocity F r = Dopplerfrequecy returnig C = Velocitiy of sound in tissue (1540 m/s) F 0 = Dopplerfrequency transmitted α = angle of insonnation Bernoulli formula Q (flowrate)= V1*A1=V2*A2 V = Velocity, A= Area If circular A= π/4*d (pipe diameter) D = Diameter

3 Prinicples of Color Doppler Prinicples of Color Doppler ALIASING NYQUIST Limit = PRF/2 NYQUIST Limit = PRF/2 ALIASING Color Doppler Color Doppler Scale or PRF: too low too high right Gain: Prinicples of Spectral Doppler Prinicples of Spectral Doppler

4 7,5 7,0 6,5 6,0 5,5 5,0 4,5 4,0 3,5 3,0 2,5 2,0 ASDIN2014 Scientific Meeting Prinicples of Spectral Doppler Prinicples of Spectral Doppler Arterial Doppler flowprofiles depending on peripheral vascular resistance Low peripheral resistance High peripheral resistance Low peripheral resistance continuous systolic and diastolic flow High peripheral resistance positive systolic flow, no or negative diastolic flow 20 What happens to the brachial artery blood flow after access creation Flow Volume Calculation =TAMV (cm/s) x Area (cm2) x 60 = Flow volume (ml/min) Diameter of the Brachial Artery Time-averaged-Mean - Velocity (TAMV) = 1/3 (Vsyst + 2 Vdiast) Diabetes mellitus mm no n = 24 yes n = 27 pre-op 1 d 10 d 6 mos Wiese, Eras, Nonnast Daniel 2004 Lomonte C et al Seminars in dialysis 2005 For accurate results All Doppler sampling should be done at an angel of 60 or less as measured between insonation beam and blood flow direction or vessel wall AVOID angles of 0! Best measure at Use STEER button Change position of the probe For accurate results Doppler sample volume placement should be in the center of the vessel Pulsed Doppler sample volume set as wide as vessel Appropriately set gain

5 Angle Diameter Time average mean V Flow Volume Critical Flow volume of access PTFE graft : < ml/min May KI 1997, 52; Strauch AJKD 1992, 19; Johnson Surgery 1998,124; Bay A J Nephrol 1998,18 AV Fistula: < ml/min Where to determine flow in a dialysis acces? Access vein? Brachial artery? Both? Besarab ASAIO J 1997,43; Bay A J Nephrol 1998, 18 Where to determine flow with ultrasound and Doppler Arguments for brachial artery flow determination Inability to measure flow in polyurethan grafts Correlates well with access flow measures (Besarab A AJKD 1997) Measurement of radial artery can underestimate flow volume as there is frequently additional flow through the ulnar artery Measurement just in the access vein can underestimate flow in case there are accessory veins Blood flow rate calculations in venous outflow often difficult due to curves, bifurcations, variations in vessel diameter, turbulent flow, material of access, superficial location, accessory veins Wiese P et al NDT 2003

6 Renal artery stenosis evaluation by ultrasound and Doppler Renal artery stenosis evaluation by ultrasound and Doppler IVC Aorta RK LK Renal artery stenosis evaluation by ultrasound and Doppler Renal artery stenosis evaluation by ultrasound and Doppler Right renal artery IVC Liver AO IVC AO Right kidney Spine Wirbelsäule Left kidney Ultrasound with Color Ultrasound with Color R RA R RA Ao Ao L RA L RA

7 Measurement of V max in RENAL ARTERY Determination of flow velocity Renal artery Aorta Renal artery V max Interlobar artery Direct measurement of renal atery flow velocity Measurement of resistance index in the intrarenal arteries V. Max > cm/sec for 60% stenosis Renal artery Interlobar artery RI Renal Resistance Index RI V Resistance index (RI), acceleraton time (AT) and parvus tardus of intrarenal Doppler spectrum AT V sys V dia No stenosis 60% stenosis 80% stenosis t RI = (V sys V dia ) / V sys NORMAL: 0,6 0,7 (but will vary with age, placement of probe, etc) parvus tardus RI is HIGH with increasing age, aortic stiffness, nephrosclerosis RI is LOW behind a stenosis or AV fistula

8 When is a stenosis significant 100 Combination of direct and indirect Doppler measurement V max > 180 cm/sec + RI difference between sides >0.05 % of normal blood flow % RI. 0, Stenosis ( % ) Textor SC Pathophysiology of renovascular hypertension, Urol Clin North Am 1984; 11: RI 0,45, ΔRI = 0,20! Combination of direct and indirect Doppler measurements Sensitivity: 96% 98 Krumme B et al(1996) Radermacher J et at (2000) Specificity: 89% 92 Voiculescu A et al. (2005) Ultrasound and Doppler Criteria for diagnosis of renal artery stenosis Duplexsonographic Criteria: Direct criteria Measurement of flow velocity in RA + Aorta Renal aortic ratio (>3,5) V max (maximal flow velocity) > (180) 200 cm/sec Indirect criteria Measurement beyond the stenosis in intrarenal vessels Resistance Index (RI), side to side difference of more than 0.05 with lower RI in the kidney behind the stenosis Acceleration time >100 ms Determinants of RI Cardiac output, blood pressure, pulse rate Diameter of vessel Compliance of big vessels Peripheral resistance Flow obstruction Summary Doppler Ultrasound is a valuable tool for determination of flow volume in a Doppler Ultrasound is also a valuable tool for screening for renal artery stenosis Understanding of Doppler and hemodynamic principles is essential for correct acquisition of flow measurements and correct interpretation of Doppler findings in the diagnosis of renal artery stenosis