Ultrasound and the dialysis patient

Transcription

1 Ultrasound and the dialysis patient Poster No.: C-1765 Congress: ECR 2011 Type: Educational Exhibit Authors: T. M. O. Couto, H. Matos, Â. Moreira, A. Estevao ; vila conde/ , Coimbra/ Keywords: Venous access, Ultrasound-Spectral Doppler, Ultrasound-Colour Doppler, Ultrasound, Vascular DOI: /ecr2011/C-1765 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 32

2 Learning objectives The purpose of this educational exhibition is to show how to explore the full potential of ultrasound in the dialysis patient. We will show: an approach to pre-operative venous mapping; the most common surgically created vascular access and their normal Doppler ultrasound appearance; evaluation of vascular access complications, such as thrombosis, stenosis, arterial steal and pseudo-aneurysm; alternative pseudo-aneurysm treatment with ultrasound guided compression. Page 2 of 32

3 Background Over the past several decades, the number of patients with end-stage renal disease on chronic hemodialysis has increased significantly. Chronic hemodialysis will likely remain the predominant renal replacement therapy Imaging and treatment of complications of vascular access has always relied on digital angiography as standard. However, advances in ultrasound, particularly Doppler, have enabled accurate evaluation of complications, even if clinically unsuspected. Page 3 of 32

4 Imaging findings OR Procedure details Patients with end-stage renal disease rely on durable, high-flow vascular conduits to obtain effective hemodialysis. To this end, a wide variety of arterio-venous (AV) fistulas and vascular grafts have been designed to provide patients with suitable means of hemodialysis (long term use of cuffed tunnel catheters should be discouraged). Kidney disease quality initiative guidelines (2006) suggest the following preferences in order: Wrist (radio-cephalic) primary A-V fistula Elbow (brachial-cephalic) primary AV fistula Transposed brachial-basilic vein fistula AV graft using synthetic material AV FISTULAS A well functioning native arterio-venous fistula is the best vascular access for the patient with end-stage renal disease. A well-developed, mature fistula lasts for a prolonged period of time, requires few interventions to maintain patency, has a low rate of infections, and improves survival on dialysis. AUTOGENOUS RADIAL-CEPHALIC FISTULA An anastomosis is constructed between the cephalic vein at the wrist to the radial artery (fig. 1). It is considered the best initial option for the patient. Most fistula failures occur within the first 12 months, beyond which the patency rates are excellent. Page 4 of 32

5 Fig.: 1. Autogenous radial-cephalic vascular wrist access (Brescia-Cimino fistula). End to side anastomosis. AUTOGENOUS BRACHIAL-CEPHALIC FISTULA An anastomosis is constructed between the antecubital veins and the brachial artery (fig. 2). A higher incidence of arterial steal (complication described below), can be expected. It also eliminates the remainder of the forearm as a possible site of future access. Page 5 of 32

6 Fig.: 2. Autogenous brachial-cephalic upper arm access. BRACHIAL-BASILIC UPPER ARM TRANSPOSITION It is usually considered a last resort access in the upper limb. The surgical procedure involves mobilization, superficial tunneling and transposition of the basilic vein with distal end-to-side anastomosis with the brachial artery (fig. 3). Page 6 of 32

7 Fig.: 3. Autogenous brachial-basilic upper arm transposition. If all upper extremity dialysis access options have been exhausted, the vascular territory of the lower extremity can be used. A loop of saphenous vein or transposition of the femoral vein are options. These vascular accesses are more likely to fail to mature, have increased incidence of steal syndrome, and suffer thrombosis earlier than upper extremity autogenous access. Page 7 of 32

8 VASCULAR GRAFTS Despite preferential placement of AV fistulas, many patients lack suitable veins for autogenous fistula creation. Most of the times native superficial veins of the forearm are too small to use effectively and, in others, all suitable veins have been utilized in prior access procedures, peripheral vascular operations, or for coronary artery bypass grafting. Polytetrafluoroethylene is the most widely used synthetic material used in the construction of prosthetic vascular graft (fig. 4). It's an inert polymer thus avoiding activation of the host's immune system, and it has the lowest coefficient of friction of any known solid material, minimizing resistance to flow. After graft placement there is a 2-4 weeks time period before the conduit can be used. There is however a special graft that allows for safe access 24 hours following implantation. Fig.: 4. Possibilities for prosthetic access construction. Sites for insertion are typically the forearm and the upper arm, in either a loop or straight configuration PATENCY RATES Page 8 of 32

9 A meta-analysis published in 2004 that reviewed 34 studies, (1,245 FE grafts) revealed an aggregate primary patency of these AV grafts of 58% and 33% at 6 months and 18 months, respectively. Secondary patency was 76% and 55% at these time intervals. The primary patency rate for autogenous fistulas was 72% and 51% at 6 and 12 months, respectively, and secondary patency rates were 86% and 77% at these intervals. US VASCULAR MAPPING The type of access placed, and its location is conventionally decided by the surgeon on the basis of physical examination results. Clinical criteria used include visible vein after tourniquet placement, a superficial course of the vein, absence of tortuous veins, an easily palpable arterial pulse and the absence of significant pressure differences (<20 mmhg) between both arms. Using this approach, only palpable veins are considered for construction of AVFs, and the more proximal draining venous anatomy is never known prior to the operation. Robbin demonstrated that preoperative sonographic mapping before placement of hemodialysis access can change surgical management with an increased number of arterio-venous fistulas placed and an improved likelihood of selecting the most functional vessels (fig. 5 and 6). The patient should be seated comfortably, with the examined arm in a stand so as to allow full access to venous anatomy by the sonographer. The forearm and upper arm are mapped separately with sequential use of a tourniquet for venous evaluation. The non-visualized part of the central veins can only be indirectly assessed sonographically by Doppler waveform analysis. The criteria used in their study for vessel adequacy are as follows: all arteries 2.0 mm or larger all veins, both in the forearm and upper arm, 2.5 mm or larger for AVF creation, or veins 4.0 mm or larger for graft creation Page 9 of 32

10 Fig.: 5. Patient with an occluded radial cephalic fistula presenting for vascular mapping. The brachial artery has adequate size and normal trifasic spectral waveform. The cephalic vein has thin wals, anecoic lumen, adequate size throughout its trajectory. Therefore a brachial-cephalic fistula should be the procedure of choice. Fig.: 6. Another patient with an occluded radial cephalic fistula presenting for vascular mapping. The image on the left reveals a normal chepalic vein at the elbow. The image on the right is at mid-arm level, where we can see an enlarged cephalic vein with luminal echogenic clot. If a fistula was built using this vein it would most likely fail to mature. ACCESS ULTRASOUND EVALUATION Page 10 of 32

11 The patient's arm is supported by a stand at a height that is confortable to the radiologist allowing easy access to the vascular territory involved in the fistula or graft (fig. 7). Fig.: 7. At our institution a gurney is lifted providing more than adequate height for comfortable access evaluation. An initial B-mode overview is obtained, providing an anatomic perception of the surgical procedure involved in the access construction. After the initial overview, color Doppler with adequate gain settings is used to look for aliasing. Spectral Doppler provides objective criteria for stenosis quantification. In AV fistulas spectral evaluation should be performed in the feeding artery cranial to the anastomoses, then the anastomoses itself, and caudal to the anastomoses in the draining vein. Grafts differ in the fact that there are two anastomoses: artery-graft; graft-vein. Measurements should be obtained in both and the midportion of the graft. Page 11 of 32

12 Also, if stenoses are identified, measurements should be obtained prior, in and distal to it. Stenosis criteria used at our institution are the same as Robbins and colleagues, and are as follows: PSV ratio across the stenosis of 2.0 or greater Visual diameter reduction of at least 50% (usually used when multiple stenosis were present) Border-line PSV ratios at the venous anastomosis, with a PSV of at least 4 m/s. Spectral Doppler evaluation of fistulas differs in arterio-venous anastomoses in which 3:1 ratio of PSV is used for significant stenosis (fig. 8). Fig.: 8. Radio-cephalic fistula with an anastomotic stenosis. PSV racio is > 4.0. Page 12 of 32

13 ACCESS VOLUME FLOW Altough not routinely used at our institution, it is possible to determine access volume flow with doppler ultrasound, giving a fast indication of the quality of the access. It is recommended to measure volume flow of native fistulas in the feeding arterial branch. FE grafts can be investigated along the entire access. The diameter of the feeding artery is determined by B-mode ultra-sonography in a transverse plane from inner edge to inner edge. The equipment software calculates the cross-sectional area. Doppler spectra is obtained for calculation of time averaged velocity in a longitudinal plane with an insonating angle maintained at <60º. Access flow is determined by equipment software. In FE grafts, access flow rates less than ml/min are associated with a significantly increased risk of failure. In native fistulas flow rates less than ml/ min probably indicate disfunction. THE NORMAL VASCULAR ACCESS Synthetic grafts are easily identified sonographically by two characteristic echogenic parallel lines (fig. 9). Page 13 of 32

14 Fig.: 9. Normal graft. Notice the parallel echogenic lines that represent graft interface with the subcutaneous tissues and bloodstream. Color and spectral Doppler in both fistula and graft should include antegrade arterialized flow without focal turbulence or visible narrowing (fig. 10). Waveforms are monophasic, with a low-resistance arterial waveform (fig. 11). Fig.: 10. This small video shows the normal color Doppler codification in a normal graft. Page 14 of 32

15 Fig.: 11. Normal AV radio-cephalic fistula anastomosis. Antegrade, low resistance arterialized flow. No morphologic evidence of stenosis. FISTULA AND GRAFT COMPLICATIONS Thrombosis and Stenosis Stenosis is the result of intimal and fibromuscular hyperplasia, caused by shear stress. Graft stenoses usually develop in the venous outflow tract at the site of anastomosis between the graft and the vein. In AV fistulas the stenosis is most often seen in the venous side, several centimeters distal to the anastomosis (fig. 12). Repeated needle puncture may have a role here (fig. 13). Although less common, stenosis of the feeding artery can also occur (fig. 14). Page 15 of 32

16 Fig.: 12. Brachial-cephalic fistula. 7 cm stenosis of the venous outflow tract. B mode with luminal narrowing and thickend walls. Color Doppler revealing aliasing and spectral Doppler showing turbulent flow with increased PSV. Page 16 of 32

17 Fig.: 13. This particular patient had a hemodialysis session just prior to the ultrasound evaluation. The US images shown are located in the needle puncture sites on the venous side of this AV fistula. Notice the echogenic clot. Fig.: 14. Brachial-cephalic AV fistula. Significant stenosis of the brachial artery. For sonographic assessment of stenosis, the vascular access is examined in the longitudinal and transverse plane from the feeding artery across the anastomosis and the arterialized draining veins as far as possible. Evaluate the perivascular space looking for functional stenoses that may result of extraluminal compression of the access by abscess or hematoma (fig. 15). Page 17 of 32

18 Fig.: 15. Hematoma compressing the venous outflow tract. Waveform reveals turbulent flow with increased PSV (>400 cm/s) Robbin reports that focal, 2 to 2.9-times PSV elevation is associated with 50%-74% stenosis, while # 3 times PSV elevation is associated with 75% or greater stenosis. The most common cause of vascular access failure is thrombosis. Particularly in grafts this is almost always the result of progressive venous outflow stenosis with decreasing access blood flow. Thombrotic oclusion of AV fistulas most frequently occur due to their inability to mature. In matured AV fistulas with severe stenoses, sonographic assessment often shows the development of collateral veins that drain the fistula and prevent complete thrombotic occlusion (fig. 16). Page 18 of 32

19 Fig.: 16. Radio-cephalic fistula. Oclusion of the cephalic vein just distal to the anastomosis. Blood flow is diverted to a nearby collateral vein (V). (A) radial artery. Arterial steal This phenomenon is defined as the presence of flow reversal in the native artery distal to the anastomosis (fig. 17). It is particularly frequent in patients with forearm and upper arm AV fistulas and in patients with prosthetic straight or loop grafts. The patient complains of hand pain or a burning sensation. Most ultrasound diagnosed steal syndromes are asymptomatic. If mild, biphasic flow may be present. Page 19 of 32

20 Fig.: 17. Radio-cephalic fistula. The image on the left reveals a radial artery prior to the anastomosis with adequate, antegrade flow. Distal to the anastomosis the flow should high resistance and antegrade. On the left a steal syndrome with retrograde low resistance flow in the distal radial artery (same patient). Pseudoaneurysms Pseudoaneurysms in grafts are likely related to insufficient hemostasis after cannulation for the dialysis session (fig 19. In AV fistulas they may also relate to improper surgical technic, and appear as early complications (fig. 18). B-mode appearance should be distinguished from hematoma. Colour Doppler will reveal a "yin - yang" pattern. Spectral Doppler will reveal a typical "to and fro" appearance (which will only be seen if the caliper is positioned in the pseudoaneurysm neck) (fig. 20) Page 20 of 32

21 Fig.: 18. Pseudoaneurysm in a AV fistula positioned in the upper arm. Shortly after the surgery, a pulsatile mass appeared due to surgical suture failure in the fistula anastomosis. Fig.: 19. Video clip showing classic graft pseudoaneurysm due to incomplete hemostasis after dialysis. Page 21 of 32

22 Fig.: 20. Typical "to and fro" waveform revealed in the spectral analysis. Ultrasound guided compression can be employed to thrombose the pseudoaneurysm. Longitudinal and transverse images should be obtained for adequate identification of the pseudoaneurysm neck. Next, compression is applied to close the neck. It is advantageous to keep the Color Doppler on to guarantee the neck is closed and no blood circulates. Thrombosis follows due to blood stasis (fig. 21). Thirty minutes of compression may be needed to achieve this goal, depending on its size (fig. 22 and 23). Page 22 of 32

23 Fig.: 21. Small pseudoaneurysm while compression is being applied. In the upper left image the content is anechoic. Notice the echogenic foci as compression is held, which translates thrombus formation. Page 23 of 32

24 Fig.: 22. Large pseudoaneurysm in a radio-cephalic fistula. "Yin-yang" pattern seen. Page 24 of 32

25 Fig.: 23. After 30 minutes of ultrasound guided compression there is no evidence of flow within the pseudoaneurysm. Once in a while compression can be reduced to ascertain the degree of thrombosis achieved. If flow is seen in the neck, or pseudoaneurysm content, compression must be resumed (fig. 24, 25 and 26). Page 25 of 32

26 Fig.: 24. The same pseudoaneurysm shown above (fig.19) prior to ultrasound guided thrombosis attempt. Page 26 of 32

27 Fig.: 25. Compression during 5 minutes. After release, flow is seen in the pseudoaneyrism neck and content. Page 27 of 32

28 Fig.: 26. Compression for 10 minutes. Flow is now only seen in the pseudoaneurysm neck. Compression must be resumed. There are some limitations for this approach to pseudoaneurysm treatment. For example, if the comunication between the pseudoaneurysm and native vessel/graft is enlarged, compression may not be possible (fig. 27). Page 28 of 32

29 Fig.: 27. Pseudoaneurysm in a radio-cephalic fistula. The diameter of the comunication to the native vessel does not allow this technique to be performed. Page 29 of 32

30 Conclusion Ultrasound equipment with Doppler capabilities are widely available nowadays. With it we can provide accurate pre-surgical venous mapping, access follow-up examination, access volume flow measurements, early and late complication assessment and even treatment as has been shown. Although angiography remains the gold standard for diagnosis and treatment we think ultrasound has an important role to play in dialysis patient care. Page 30 of 32

31 Personal Information First author: Tiago Couto Institution: Centro Hospitalar de Coimbra Page 31 of 32

32 References US Vascular Mapping before Hemodialysis Access Placement; Robbin et all; Radiology 2000; 217:83-88; Effect of preoperative sonographic mapping on vascular access outcomes in hemodialysis patients; Allon et all; Kidney International, 2001; 60: ; Color Doppler Sonography of Hemodialysis Vascular Access: Comparison with Angiography; Middleton et all; AJR 1989;152: ; Colour Doppler ultrasound in dialysis access; Wiese et all; Nephrol Dial Transplant 2004; 19: ; Colour Doppler ultrasound assessment of well-functioning mature arteriovenous fistulas for haemodialysis access; Pietura et all; European Journal of Radiology 55 (2005) ; Hemodialysis Arteriovenous Fistula Maturity: US Evaluation; Robbin et all; Radiology 2002; 225:59-64; High Resolution Real-Time Sonography of Hemodialysis Complications; Scheible et all; AJR 1980:134: Vascular Access Page 32 of 32