Ultrasound has important advantages in preoperative diagnosis of hemodialysis access, intraoperative positioning, and postoperative follow-up. It is a necessary skill for vascular access physicians. Ultrasound-guided endocavity technology does not require special equipment and can be performed at the bedside (POCUS). It is suitable for the characteristics of fast processing of internal fistula complications, while avoiding the application of contrast agents. It has the advantages of real-time display, multi-angle imaging, and low cost. It is safe in clinical practice. It is effective and can be applied to the treatment of puncture approach, stenosis or occlusive disease and pseudoaneurysm. Unique advantages are on ultrasound-guided endocavity technology and conventional radiological-guided endocavity technology. Digital subtraction and angiography pay more attention to the whole, and ultrasound is better in details. It needs to be rationally applied for any kind of methods.
Hemodialysis access is the lifeline of hemodialysis patients. With the development of the times and the advancement of equipment, patients’ dialysis age is getting longer and longer. The establishment and maintenance of hemodialysis pathways are becoming increasingly important. Because the arteriovenous fistulas are mostly established in the upper extremities, the position of the vessels is superficial and interference. Ultrasound diagnosis has high accuracy, specificity and sensitivity. The accuracy of measuring residual stenosis is similar to the current gold standard angiography. The sensitivity and specificity of stenosis in various parts of the venous access are similar to that of multi-slice spiral CT. If the two are used in combination, it can reach 100% accuracy. Ultrasound is an important method for evaluating vascular conditions before hemodialysis access, monitoring and follow-up blood flow after surgery, diagnosing complications, and positioning the operation.
Due to the superficial location of the arteriovenous fistula, the tissue structure and percutaneous transluminal angioplasty (PTA) related equipment (such as vascular sheath, guide wire, balloon) echo contrast is good, so ultrasound can clearly show the vascular structure. And interventional equipment provides the possibility of ultrasound-guided endocavity technology. In 2000, Bacchini et al. first applied ultrasound-guided PTA to graft arteriovenous fistulas. After 12 cases of artificial vascular arteriovenous fistula stenosis PTA treatment, the internal diameter of the stenosis and the natural blood flow of the passage were significantly increased without complications. Since then, the technology has been further extended to autologous arteriovenous fistula stenosis and even occlusive disease. Japanese scholar Wakabayashi performed 4896 operations in 1011 cases, of which 4414 were stenotic lesions. The technical and early success rate reached 97.1%, and 455 occlusive lesions. The technical and early success rate reached 97.4%. There were 12 cases (0.2%) of the cases had bleeding and other complications, including 4 cases of small leakage, 3 cases of pseudoaneurysms requiring surgical repair, 5 cases of bleeding, of which 2 cases were surgically repaired, and 3 cases were hemostatic after balloon compression. This shows that ultrasound-guided intracavitary treatment of hemodialysis pathways is feasible, safe and effective.
The basic steps of ultrasound-guided PTA
Ultrasound-guided PTA indications: According to the Chinese Expert Consensus on Vascular Access for Hemodialysis (Second Edition), the indication for stenosis intervention is that the stenosis exceeds 50% of the surrounding normal vessel diameter with the following conditions such as: internal fistula natural blood flow <500 ml/ min; the blood flow required for the dialysis prescription cannot be met; the dialysis venous pressure is increased; puncture is difficult; the adequacy of dialysis is decreased and the internal fistula has abnormal signs.
Ultrasound preoperative evaluation: determine the location, length, degree of stenosis, whether it is complicated with thrombosis and calcification. The blood vessel diameter, resistance index and peak systolic velocity ratio (PSVR) can be measured. Although it is not a direct morphological index, it can indirectly help identify morphological stenosis. A resistance index greater than 0.6 may have stenosis, and a resistance index greater than 0.7 may have severe stenosis. PSVR is to indirectly estimate the degree of reduction of the inner diameter of the stenosis by measuring the multiples of the peak flow velocity during the systole of the stenosis and the normal part. Determining the location of the lesion and marking the body surface is helpful to facilitate the intraoperative operation. When the fistula vein runs straight from the access site to the stenosis site and has fewer collateral branches, it is completely possible to use an ultrasound probe to wait for the guide wire to arrive at the lesion site. There is no need for the probe to follow all the way, and the requirements for the surgical assistant can be reduced accordingly. Except for the stenosis, the diameter of the adjacent normal vein should be measured to select the appropriate size balloon. At the same time, observe the anatomical structure of the anastomosis to choose an appropriate approach to place the vascular sheath, and try to choose a straight, less curved treatment path.
Approach selection: It is an important part of ultrasound-guided PTA treatment. A suitable approach can greatly shorten the operation time and achieve a multiplier effect with half the effort. Depending on the location of the stenosis, the degree of stenosis and the local anatomical configuration, the direction of the approach can be reverse, forward, or two-way, and the sheath can also be selected in a sufficiently thick approach vessel. It is hoped that all lesions can be covered through this approach, and the path should be straight and smooth. Special consideration should be given to severe valvular stenosis, and it is easier to pass the lesion in the direction of blood flow. Try not to choose the location of the bifurcation sheath to avoid local thrombosis affecting both blood vessels at the same time. The sheath tip is as close as possible to the diseased site but sufficient operating space is guaranteed, and at the same time, the sheath has enough length to be indwelled in the blood vessel to avoid slippage of the sheath during operation. The puncture site has a sufficient diameter, which is twice the diameter of the sheath, to avoid local thrombosis caused by the indwelling sheath. Try to choose a superficial, easy-to-puncture, and easy-to-stop bleeding site. Commonly used approaches are fistula vein, artificial blood vessel, distal radial artery, and proximal artery. Artificial blood vessel and venous approach are preferred, internal fistulas are not mature enough, and arterial approach should be considered for fistula vein details.
Puncture sheath: For cases where the blood vessel is deep and thin, and it is not easy to penetrate directly, ultrasound-guided puncture is safer, simpler and more accurate. The direction and depth of the puncture are clearly defined in the cross section. Once the breakthrough is made, the longitudinal axis clearly defines the puncture needle in the lumen. It is worth noting that the trocar core is longer than the cannula, so once there is blood return, the cannula must be pushed down and pushed forward to avoid the cannula not entering the blood vessel and avoiding the blood vessel. The diameter of the sheath is selected according to the diameter of the balloon. Usually, a larger size vascular sheath is selected to facilitate operation and avoid poor retraction of some balloons and difficulty in passing through the same-sized vascular sheath again. For fistula veins that are too thin, choose the same specification vascular sheath.
Guide wire through the lesion: different from digital subtraction angiography (DSA), ultrasound-guided operation, relative to the limitation of the operating table, the corresponding use of catheter exchange guide wire is limited by space, so it is simple to operate, mostly bare guide The wire passes through the lesion instead of the catheter carrying the guide wire. After choosing the approach, most of the diseased straight head guide wires are easier to pass through the lesion than the J-shaped head guide wires without catheter guidance. Therefore, the straight puncture guide wires of the vascular sheath suit are often used to directly pass through the lesion, and the vascular sheath core follows. After the stenosis, it is changed to a J-shaped head long guide wire, and then followed by a balloon catheter. In most cases, the stenosis can be passed smoothly through the sheath core guide, which plays a role in the exchange of catheters. At this time, the choice of approach needs to consider whether the sheath core can pass the lesion smoothly. When the conventional route cannot be passed, consider the catheter finger guide wire or 0.018 inch (1 inch = 0.0254m) guide wire to pass the lesion. The key is to determine the direction of the catheter guide wire advancement by ultrasound, and avoid entering the collateral branch. Sometimes the body surface can compress the side Support to facilitate the guide wire to get back on track.
Balloon expansion: For curved lesions, especially over anastomotic lesions, the guide wire must have sufficient support to facilitate the passage of the balloon catheter. The guide wire needs to be deep enough (often to the brachial artery) or replaced with a stronger guide wire. The balloon is selected according to the diameter of the adjacent blood vessel behind the beam arm, usually a 4-7 mm balloon. It should be noted that the general expansion pressure is based on the fully opened waist of the balloon, and does not need to reach the burst pressure level. There are different opinions about the duration of 30s to 3 min. Some scholars believe that slow pressure can reduce the pain during expansion. Stents can be used to remedy cases with poor expansion effects. However, the stent grafts are not clearly displayed due to echo effects. It is not recommended to place the stent grafts under ultrasound guidance.
Evaluation of treatment effect: After the expansion, the guide wire remains in place to evaluate the treatment effect. Physical examination should be combined with two-dimensional color doppler ultrasound images, color doppler blood flow images, doppler spectrum changes and comprehensive evaluation of hemodialysis after treatment; usually, the original abnormal signs of internal fistula should disappear after successful PTA treatment: Increased tremor, disappearance of pulsation, etc. may occur; in addition to two-dimensional images that can directly understand the correction of stenosis lesions, the success of the treatment can also be judged by the decrease in brachial artery resistance index and the increase in blood flow. Studies have shown that the blood flow measured by vector blood flow imaging is equivalent to the ultrasound dilution method, and can be used as a method for blood flow measurement to assess whether complications such as thrombosis and bleeding occur. Small bleeding can generally be controlled by continuing balloon expansion and compression.
Other problems: During the operation, the appropriate dose of anticoagulation therapy is selected according to the coagulation status and the operation time. The appropriate local anesthesia or nerve block anesthesia is selected according to the patient’s tolerance to pain. It is worth noting that local anesthesia should not be placed on the superficial surface of the blood vessel as much as possible. Combined with thrombus, thrombus load is small, it can be directly balloon expanded after thrombolysis, or thrombus can be grasped by vascular sheath aspiration or grasping forceps. Mechanical thrombolytic catheters have certain effects but are expensive. For cases with heavy thrombus load or many old thrombuses, hybrid surgery can be considered, and the stenotic lesions can be treated under ultrasound guidance after a small incision to remove the thrombus.
Advantages and disadvantages of ultrasound-guided PTA and radiation-guided PTA
Advantages:
- Ultrasound guided PTA treatment does not require special radiological equipment and can be completed in an ultrasound room or an ordinary operating room, with low cost.
- Prevent patients and medical staff from being injured by X-ray radiation.
- To avoid the risk of contrast agent allergy and residual kidney function damage, it is particularly important to avoid contrast agent affecting residual kidney function in patients with poorly mature arteriovenous fistulas who have not yet entered dialysis.
- In terms of therapeutic approach puncture, ultrasound can guide the micropuncture needle to puncture the blood vessel in real time to establish a therapeutic approach. Because ultrasound can display the vessel wall and intraluminal structure, ultrasound-guided puncture is more accurate and safe.
- Two-dimensional ultrasound can accurately measure the inner diameter of the normal blood vessel adjacent to the lesion, which helps to select a balloon of appropriate size.
- Before dilation treatment, ultrasound can guide local injection of local anesthetic drugs, and a small dose of local anesthetic drugs under the three-dimensional structure can exert obvious effects and relieve the pain of patients.
- The display of local details by ultrasound is a three-dimensional structure, which is better than dsa. It is reflected in: (1) In terms of preoperative diagnosis, for vascular concentric stenosis, the two have the same diagnostic value; but internal fistula stenosis is more eccentric stenosis caused by intimal and media hyperplasia, when the hyperplasia is located in the sagittal shape In the face, radiological diagnosis is limited by its two-dimensional imaging, which may lead to missed diagnosis of stenotic lesions. Valvular stenosis is also easily missed in DSA. (2) In occlusive lesions or multi-branch lesions, ultrasound can clearly indicate the direction of the guide wire advancement, and can promptly detect whether the interventional device has penetrated the blood vessel, indicating the direction for the sharp opening. (3) Clearly display the position of thrombus or foreign body in the cavity, which is convenient for catheter suction, broken thrombus or clamp removal. (4) When using balloon thrombus to treat artificial blood vessel arteriovenous fistula thrombosis, the squeezing of the balloon at the artificial vascular arterial anastomosis will cause the thrombus to be squeezed and fall off to the artery lumen, causing arterial embolism, and ultrasound is real-time Observe the thrombosis. Once there is a risk of falling off, the balloon can be dragged to avoid arterial embolism.
Disadvantages
- The overall assessment is poor, not as intuitive, efficient and clear as DSA. (1) Poor visualization of the parts affected by echo, such as deep structure, severe calcification, and obesity surgery. (2) The central vein cannot be displayed. Currently, the lesions of the cephalic venous arch and the distal subclavian vein can be clearly displayed. The confluence of the innominate vein and the subclavian vein can be displayed with the pediatric convex array probe, but it is not as good in the diagnosis and treatment of the central vein DSA. (3) The detection range is limited by the length of the probe, and multiple images are required to synthesize images when blood vessels travel and bend. DSA is more intuitive. Delineating ultrasound blood vessels is more time-consuming than imaging, and comprehensive evaluation is lacking. (4) DSA can also observe the flexibility of the tube wall. Adjacent lesions with severe stenosis, such as poor flexibility, will be treated as lesions during treatment. Ultrasound pays more attention to the diameter, and may ignore the lesions with acceptable diameter and stiff tube wall. .
- In addition to the operator, at least one physician with ultrasound skills is required to cooperate on the operating table.
- The operating space is less than DSA, and it is more suitable for interventional instruments with short working distance. However, the existing stents and exchange catheters require a working distance of more than Im, which increases the difficulty of operation.
- The precise location and traceability of the stenosis during follow-up are not as good as DSA.
- DSA judges the residual stenosis based on the contrast image without any dispute. However, the evaluation system after ultrasound needs to be perfected. From the cases with no residual stenosis after PTA, the ultrasound images are not so perfect, and there is no case that the diameter of the blood vessel after expansion reaches the diameter of balloon expansion. At present, our center uses more physical examinations with postoperative stenosis up to 3 mm in diameter and brachial artery flow rate up to 600 ml/min as the end of the operation standard. This standard needs further study.
At present, there is no comparative study of ultrasound intervention and radiotherapy in the treatment of arteriovenous fistula stenosis. But from the treatment research of ultrasound intervention, the two have similar effects in the early patency rate and complications. Bacchini and other follow-up patients who underwent ultrasound-guided PTA therapy found that the risk of thrombosis decreased by 64%, the secondary patency rate at 18 months was 80%, and the patients without PTA therapy were 58%.
Ultrasound-guided endocavity technology can be used in the treatment of pseudoaneurysms in the hemodialysis pathway in addition to the treatment of puncture access, stenosis or occlusion. Ultrasound is the first choice for diagnosing and ruling out pseudoaneurysms. Its sensitivity can be as high as 94%-97%. It is often found that the sacs connected to the artery through the sinus or the neck of the aneurysm, single or multi-chamber, can be explored. Blood flow signal. Thrombin injection therapy under ultrasound positioning is to introduce a 22G puncture needle into the tumor cavity under direct ultrasound. The needle tip is located in the center of the tumor body, and thrombin is injected directly into the tumor cavity until the blood flow signal in the tumor cavity disappears. Thrombin can promote the conversion of fibrinogen into fibrin and then thrombosis, so it can accelerate blood thrombosis in the tumor cavity. A large number of documents have confirmed the safety and effectiveness of this method. The overall tumor cavity thrombosis rate can be as high as 86% to 100%, and most can be cured with one treatment, and the recurrence rate is only 0% to 9%. However, for wide tumor necks, care should be taken to prevent thrombin from overflowing into the artery and causing arterial ischemia. The artery can be blocked by a balloon to assist thrombin injection.
Ultrasound has important advantages in preoperative diagnosis of hemodialysis access, intraoperative positioning operations, and postoperative follow-up, and it is an essential skill for access physicians. DSA pays more attention to the whole, and ultrasound is better in details: ultrasound-guided endocavity treatment has advantages that DSA does not have, but it also has its shortcomings. The two complement each other. Ultrasound is more suitable for grassroots development. On the basis of mastering the basic ultrasound diagnosis and the basic norms of endocavity treatment, the surgeon should carry out clinical practice from easy to difficult, accumulate certain experience, and then carry out large-scale development to better serve patients.