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Techniques of Ultrasound Evaluation of Vascular Access

2. Vascular access (VA) is the

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Techniques of Ultrasound Evaluation of Vascular Access

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    1. Techniques of Ultrasound Evaluation of Vascular Access Marko Malovrh University Medical Centre Ljubljana Department of Nephrology Ljubljana, Slovenia

    2. 2 Vascular access (VA) is the “life line”of dialysis pts. VA is prone to frequent complications before and after creation.

    3. 3 Native arteriovenous fistula (AVF) is superior to an AV graft and a catheter, due to its lower complication and higher patency rates. Number of elderly, with co-morbid conditions (diabetes, vascular disease) is increasing – the creation and maintenance of functional VA is not an easy task.

    4. 4 To establishing reliable VA for haemodialysis: Careful planning Preoperative evaluation: Medical history Physical examination Ultrasonography

    5. 5 US is non-invasive, low cost and there is no need for radiocontrast. The main disadvantage of US is: Operator dependency Additional knowledge to interpret DU: Changes in local vascular haemodynamic after VA creation Patophysiological mechanisms behind VA complications

    6. 6 Ultrasound is sound above the audible range – frequency above 20.000 Hz. B mode real time ultrasound scanning: Allows visualization of structures as being: black (blood, fluid..) grey (solid organs..) white (vessels, calcifications..) Rapid rate of changes provide a real time B mode ultrasound scan

    7. 7 By Doppler ( color D, pulsed wave D, power mode D) we can obtain information: On the direction ob blood flow On the velocity of blood flow Combination of B mode US and DU- Duplex Ultrasound - linear high frequency transducer (8-12 MHz)

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    9. 9 HEMODIALYSIS VASCULAR ACCESS ULTRASONOGRAPHY Preoperative vascular ultrasound: In addition to clinical assessment improves AVF outcomes in terms of patency Improves maturation and use of AVF for dialysis Intraoperative examination: Confirm pre-op studies Assess the impact of fistula flow on the artery inflow Assess the flow in the fistula vein Evaluation of VA: Measurement of access flow Detection of complications (stenosis, steal, thrombosis)

    10. 10 Preoperative vascular ultrasound Clinical examination first! Patient is in supine position Non-dominant arm first Stable local conditions Start with vein mapping Continue with arteries

    11. 11 VEIN MAPPING Apperance of the vein At the upper part of upper arm put tourniquet or cuff for blood pressure measurement inflated 70 to 80 mmHg Trace cephalic vein from distal part of forearm toward cubital fossa Assess anatomy, size and suitability of upper arm cephalic vein Trace basilic vein from the wrist to its insertion to brachial or axillary vein Not useful for central veins

    12. 12 Examine all the veins for continuity, including major accessory branches, evidence of intramural or intraluminal thrombus or stenosis Measure internal diameter at different parts of veins and wall thickness After releasing tourniquet/cuff measure internal diameter - difference is distensibility (IID) VEIN MAPPING

    13. 13 Measure the depth of the vein. Test changes of venous Doppler signal during deep respiration; increasing of venous flow during inspiration - indirect sign for no venous outflow stenosis. Choose the most distal part of suitable vein. VEIN MAPPING

    14. 14 Start artery assessment at the nearest place of suitable vein. Assess anatomy, quality of artery (radial, brachial or ulnar), luminal diameter, wall thickness and amount of calcification. ID = 2 mm ARTERIAL EVALUATION

    15. 15 Assess Doppler waveform, systolic velocity (SV), diastolic velocity (DV). Normal Doppler waveform is high resistance, triphasic with RI = 1. ARTERIAL EVALUATION

    16. 16 ARTERIAL EVALUATION Consider reactive hyperaemia test with clenching the fist for 2 minutes or by pneumatic cuff inflator 20-30 mmHg above systolic pressure for 2 minutes and calculate RI after releasing the fist. RI = 0.7 or at least change HRF to LRF. Normal Doppler waveform of feeding artery for arteriovenous fistula or graft is low resistance with RI < 1.

    17. 17 POSTOPERATIVE USE OF ULTRASOUND To evaluate maturation or non-matured AVF To evaluate early or late AVF and AVG complications

    18. 18 POSTOPERATIVE USE OF ULTRASOUND – nonmatured AVF Test should be done 4-6 weeks after AVF creation if AVF is clinically non-matured: B mode ultrasound provide diameter, depth and length of fistula vein and internal diameter of the feeding artery (should be increased. Brachial artery as inflow artery for upper arm vascular access flow measurement provides indirect measure of fistula flow (ID and TAV).

    19. 19 POSTOPERATIVE USE OF ULTRASOUND – nonmatured AVF Measurement of access flow: It should be measured in a straight vascular segment (venous outflow not to very wide – less than 7 mm) Segment should be at least 5 cm away from anastomosis Brachial artery is recommended – 20% have high bracial artery bifurcation !!) Longitudinal axis of blood vessel (diameter) and TAV Modern US devices have special software for calculatinfg blood flow from ID and TAV

    20. 20 POSTOPERATIVE USE OF ULTRASOUND – nonmatured AVF The most common reason for low arterial inflow is juxta anastomotic stenosis or proximal stenosis of the feeding artery or outflow stenosis.

    21. 21 POSTOPERATIVE USE OF ULTRASOUND – nonmatured AVF Diagnostic criteria for hemodinamiucally significant stenosisi: Increasing of RI in feeding artery Diameter narrowing (B-mode) by >50% >2 fold increase of peak systolic velocity Post stenotic turbulence

    22. 22 POSTOPERATIVE USE OF ULTRASOUND – nonmatured AVF Ultrasound provides a good visualization of haematoma or seroma around fistula vein or graft, depth of graft and graft tissue incorporation.

    23. 23 POSTOPERATIVE USE OF ULTRASOUND – access complications evaluation Should be used in conjunction with clinical examination to evaluate access dysfunction. The most common complication is outflow stenosis. Ultrasound provides visualisation of chronic thrombus within large aneurismal dilation when problems with needling are present.

    24. 24 POSTOPERATIVE USE OF ULTRASOUND – access complications evaluation Steal phenomenon is more and more frequent, particularly in patients with forearm and upper arm AVFs and in patients with prosthetic straight or loop grafts. Assessment of the access-feeding artery by investigating the parts proximal and distal to the anastomosis. US sign for steal syndrome is change in flow direction.

    25. 25 CONCLUSION Duplex ultrasonography is a useful tool to optimize vascular access care in hemodialysis patients. Appropriate equipment, local conditions and knowledge about haemodynamics before and after vascular access creation are obligatory.

    26. 26 CONCLUSION Routine preoperative ultrasound in addition to clinical assessment improves AVF outcomes in terms of patency and use for dialysis. In case of access complications, after clinical evaluation, initial anatomic and functional assessment may be best performed by non-invasive duplex sonography, followed by other imaging methods, including intervention.

    27. 27 THANK YOU FOR YOUR ATTENTION

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