Fluidodynamic Evaluation of Arteriovenous Fistulae for Hemodialysis

Arteriovenous fistulae (AVF) are commonly used in dialysis treatment of uremic patients. However, many AVF create problems and have to be re-examined. Problems arise in the cannulation site and must be treated with antibiotics, and stenosis, both in the arterial and in the venous side of the AVF. In the worst case, the AVF must be replaced for treatment to continue. However, this can only be repeated once before the AVF site is no longer viable. This increases the discomfort, the morbidity and the mortality of the dialysis patient. Several kinds of AVF were studied to determine whether flow disturbances give rise to these complications. Many studies have already demonstrated the importance of hemodynamic factors in vascular disease pathogenesis. These factors include: the pulsatility of flow, the elasticity of the vessel, the non-Newtonian blood, flow behavior and, very importantly for AVF, the vessel geometry. In model studies, intimal changes have been observed in bends and bifurcations, regions of vessel construction and vessel stenosis. In these regions, blood flow changes abruptly and this contributes to arterial disease. We prepared several one-to-one, true-to-scale elastic silicon rubber models of different AVF. The AVF models were based on angiographic studies of chronic dialysis patients and on AVF from the arms of cadavers. The models had a similar compliance to that of the human blood vessel. Flow was visualized using photoelasticity apparatus and a birefringent blood-like fluid. This method is suitable to analyze the spatial configuration of flow profiles, to differentiate laminar flow from disturbed flow, and to visualize flow separation, vortex formation and secondary flow. It was found that AVF create disturbances that are not found under normal physiological flow conditions. The X-formed AVF was very unsatisfactory, creating significant flow disturbances. The AVF had high velocity fluctuations. These could lead, for example, to aneurysm formation. A better configuration would be an end-to-end AVF. However, this formation creates other complications. For example, there is not enough blood to the hand and parts of the hand lose feeling. The recommended AVF would be an end-to-side anastomosis. In this case, attention is needed for placement geometry, to minimize additional flow disturbances. Several models as well as patient angiographic studies are discussed.

Preliminary Results of Anaconda™ Aortic Endografts: A Single Center Study

OBJECTIVE

To evaluate the peri-operative results of Anaconda endograft in the first 49 cases treated in a single centre.

METHODS

The study was carried out prospectively on cases of infrarenal abdominal aortic aneurysm (AAA) treated with Anaconda endograft. The characteristics of the proximal aortic neck and of the iliac access vessels were considered. The following operative results were assessed: the main body oversizing, the need to correct the positioning of the main body, the use of iliac extensions, the use of ballooning, the covering of patent hypogastric arteries, the presence of endoleaks and the need for conversion. Peri-operative (30 days) mortality and morbidity were also considered.

RESULTS

Of the 49 cases treated, 44 were males with a mean age of 73 years (range: 55-89 yrs; SD+/-7 yrs). The mean diameter of the AAA was 56 mm (range 45-91 mm; SD+/-11); 4 cases had common iliac aneurysms with a diameter >3 cm. The mean neck diameter and length were 23 mm (range 19-28 mm; SD+/-3) and 25 mm (range 15-50 mm; SD+/-10) respectively. An aortic neck angle between 40 degrees and 70 degrees was present in 10 cases (20%) (mean 58 degrees; SD+/-15 degrees), and 20 cases (41%) had iliac tortuosity with an angle greater than 60 degrees (mean 85 degrees; SD+/-25 degrees). There were no cases of conversion or intra-operative death. One (2%) peri-operative death occurred, for reasons not related to the endograft. There were two cases of iliac limb thrombosis. CT at one month showed 12 cases (25%) of type II endoleak. There were no cases of type I or type III endoleaks.

CONCLUSIONS

The preliminary data of this series demonstrates that the Anaconda endograft has good peri-operative results in the treatment of infrarenal AAAs with a neck length not less than 15 mm.

[Refractory hypertention in a female patient with renal failure]

We report one sixty-seven years-old female who presented with hypertension refractory to antihypertensive drugs. She had an elevated BP for approximately 15 years. In the last 8-10 months her hypertension had become difficult to control. Her BP ranged between 180/100 mmHg and 220/1220 mmHg on atenolol 100 mg once daily, methyldopa 500 mg three times daily, furosemide 25 mg twice daily, doxazosine 4 mg twice daily. When she was referred to our unit serum creatinine was 2.3 mg/dL and she had a mild proteinuria (70 mg/dL) without microematuria. Ultrasonography showed a left kidney size in the low-normal range (LD 11 cm) and a small right kidney (LD 9 cm). Renal angiography showed a severe, ostial stenosis of the left renal artery and a total thrombosis of the right renal artery with a blood supply to the right kidney provided by collateral channels. An ACE-I was added to the therapy but a sharp increase in serum creatinina (up to 6.4 mg/dL) prompted us to withdraw the drug. She underwent a renal angioplasty on the left side and a Palmaz stent was placed. The control angiography showed a good anatomical result. Three months after the manoeuvre the patient was again referred to our unit with headache, nausea vomiting and hyper-tension refractory to amlodipine 10 mg/day, doxazosine 4 mg twice a a day, atenolol 50 mg/day, furosemide 50 mg/day. A doppler ultrasonography and a magnetic resonance angiogram showed no restenosis on the treated artery. An ACE-I was again administered and BP on this drug was 145/90 mmHg after one month and 130/85 after three months. Headache, nausea and vomiting disappeared. Serum creatinina kept unchanged (2.2 mg/dL). Comment. In this case the benefit of angioplasty on blood pressure control was indirect. Apparently the manoeuvre showed no effect on blood pressure, but the angioplasty allowed us to use of an ACE-Inhibitor, without any negative effect on renal function, and thus to adequately control blood pressure.

Fluidodynamic evaluation of arteriovenous fistulae for hemodialysis

Arteriovenous fistulae (AVF) are commonly used in dialysis treatment of uremic patients. However, many AVF create problems and have to be re-examined. Problems arise in the cannulation site and must be treated with antibiotics, and stenosis, both in the arterial and in the venous side of the AVF. In the worst case, the AVF must be replaced for treatment to continue. However, this can only be repeated once before the AVF site is no longer viable. This increases the discomfort, the morbidity and the mortality of the dialysis patient. Several kinds of AVF were studied to determine whether flow disturbances give rise to these complications. Many studies have already demonstrated the importance of hemodynamic factors in vascular disease pathogenesis. These factors include: the pulsatility of flow, the elasticity of the vessel, the non-Newtonian blood, flow behavior and, very importantly for AVF, the vessel geometry. In model studies, intimal changes have been observed in bends and bifurcations, regions of vessel construction and vessel stenosis. In these regions, blood flow changes abruptly and this contributes to arterial disease. We prepared several one-to-one, true-to-scale elastic silicon rubber models of different AVF. The AVF models were based on angiographic studies of chronic dialysis patients and on AVF from the arms of cadavers. The models had a similar compliance to that of the human blood vessel. Flow was visualized using photoelasticity apparatus and a birefringent blood-like fluid. This method is suitable to analyze the spatial configuration of flow profiles, to differentiate laminar flow from disturbed flow, and to visualize flow separation, vortex formation and secondary flow. It was found that AVF create disturbances that are not found under normal physiological flow conditions. The X-formed AVF was very unsatisfactory, creating significant flow disturbances. The AVF had high velocity fluctuations. These could lead, for example, to aneurysm formation. A better configuration would be an end-to-end AVF. However, this formation creates other complications. For example, there is not enough blood to the hand and parts of the hand lose feeling. The recommended AVF would be an end-to-side anastomosis. In this case, attention is needed for placement geometry, to minimize additional flow disturbances. Several models as well as patient angiographic studies are discussed.

Renovascular disease in diabetes mellitus: treatment by percutaneous transluminal renal angioplasty

BACKGROUND

Diabetes mellitus is an important cause of end-stage renal failure (ESRF). Although classic diabetic nephropathy accounts for the majority of patients reaching ESRF, renovascular disease, which is frequent in such patients, plays an increasingly important role. Percutaneous transluminal renal angioplasty (PTRA) has been proven to be an efficacious measure for renal revascularization.

METHODS

Ninety-nine patients with diabetes mellitus and renal artery stenosis, corresponding to 16.6% of the entire population of diabetic patients, were treated by PTRA or with the Palmaz-Schatz stent in our clinic. Technical success was achieved by PTRA in 92/99 patients, in 10 patients a Palmaz-Schatz stent was implanted.

RESULTS

Hypertension was cured in eight and improved in 44 patients. In 47 patients, there was no impact on blood pressure. An improvement in renal function was evident 1 month after PTRA in 8/27 patients. A further improvement occurred in another four patients after 6 months. The re-stenosis rate was 22% after 5 years. Serious complications occurred in seven patients (one patient required surgery and two patients had regular dialysis treatment).

CONCLUSIONS

Renovascular disease is an important cause of ESRF in diabetic patients. PTRA is a valid tool to revascularize renal artery stenosis and improve blood pressure control and renal function both in diabetic and non-diabetic patients.

Renal artery angioplasty for renovascular hypertension and preservation of renal function: long-term angiographic and clinical follow-up

OBJECTIVE

Percutaneous transluminal angioplasty of stenoses of the renal artery can be used to treat hypertension and renal insufficiency. Although many studies have been published on the short-term results of this procedure, few long-term studies are available.

SUBJECTS AND METHODS

One hundred ninety-five patients (123 men and 72 women 19-79 years old; mean age, 56 years) with stenosis of the renal artery and hypertension underwent renal percutaneous transluminal angioplasty at our institution. The stenosis was unilateral in 66% of patients, bilateral in 26%, and in a solitary functioning kidney in 8%. Renal insufficiency was present in 31% of patients. After renal percutaneous transluminal angioplasty, long-term clinical and angiographic follow-up was evaluated by life-table analysis.

RESULTS

In patients with fibromuscular disease, blood pressure returned to normal in 57%, improved in 21%, and was unchanged in 21%. In patients with atherosclerotic stenosis, blood pressure returned to normal in 12%, improved in 51%, and was unchanged in 37%. After percutaneous transluminal angioplasty, renal function improved in 48% of patients with renal insufficiency due to bilateral stenosis or stenosis in the single functioning kidney, whereas none of the patients with unilateral stenosis of renal artery and renal insufficiency had any notable improvement. Long-term follow-up showed a high rate (82%) of patency of revascularized arteries and a low rate (21%) of hypertension recurrence at 5 years.

CONCLUSION

Renal percutaneous transluminal angioplasty is useful for treating hypertension and for reestablishing renal function. Its effects on blood pressure and renal function are long-lasting in the large majority of patients.

[Color-Doppler and angioplasty in renovascular hypertension]

Renovascular hypertension is defined as a kind of hypertension secondary to altered renal perfusion with the activation of the renin-angiotensin system. Since a large number of these patients benefits from treatment--be it medical, surgical or angioplastic--a non-invasive low-cost method allowing accurate screening was looked for. Color-Doppler was employed by many authors to evaluate renovascular hypertension, for both the early diagnosis of the condition and the evaluation of treatment results in renal artery stenoses. However, the authors agree that color-Doppler cannot play a major role in the screening of renovascular hypertension due to the various qualitative and quantitative variables not being adequately codified, to the lack of a single color-Doppler method and to the difficult comparison of the results from the different units. Nevertheless, improved results are promised by technological evolution, together with the possibility to codify color-Doppler variables more easily repeatable. B-mode units with 3.5 and 5 MHz probes were employed in the thinnest subjects. In 5-25% of cases accessory renal arteries were observed. After identifying the vessel to be studied with several spatial scans, the smallest possible sample volume (usually 3-5 mm) was positioned. The normal flowmetric range was 0.07-0.1 s: it must not exceed 0.16 s, with persistence of high diastolic flow. Some authors' criteria were followed to define either stenosis or renal artery obstruction; moreover, pulsatile flow index was considered, together with the resistive index, pulsatility index and stenosis index.

[Renal artery stenosis. Doppler color study before and after angioplasty]

Doppler flowmetry can be successfully employed to assess arterial patency after percutaneous transluminal angioplasty (PTA). The aim of this study was to assess color Doppler sensitivity in detecting renal artery stenosis prior to percutaneous angioplasty (PTRA) and vessel patency after it. Eleven patients (7 males and 4 females) affected with renal artery stenosis, unilateral in 9 cases and bilaterally in 2, underwent color-Doppler evaluation 1 day before and 7 days after PTRA. The operator was unaware of dilatation results. A total of 13 stenoses were treated. The qualitative and quantitative parameters we employed were: a) broadening of the spectrum, b) peak systolic frequency > 4000 Hz, c) stenosis index > 50%. Before PTRA, mean systolic peak at the stenosis was 7978 (range 4050-12500 Hz), while stenosis index was 71.9% (range 48-89%). After PTRA complete recovery was observed in 5 cases, no improvement in 1 and incomplete recovery in 7. Doppler results were in agreement with those of angiography in 6/13 while partial agreement only was seen in 7/13. Our results, although obtained in a small and highly selected group of patients, would seem to support the value of color-Doppler for the follow-up of patients after PTRA.

Prognostic value of captopril renal scintigraphy in renovascular hypertension

This study evaluates the prognostic value of captopril renal scintigraphy in hypertensive patients undergoing renal artery revascularization. Preoperative studies of 51 patients were correlated with blood pressure results at 6- and 12-mo follow-up. Captopril-renal scintigraphy was carried out 1 hr after oral administration of 50 mg of captopril, using either 220 MBq of 99mTc-DTPA or 74 MBq of 99mTc-MAG3, followed by a baseline study in case of abnormal results. Evidence of amelioration or normalization in relation to captopril study was considered predictive of blood pressure control following treatment. Blood pressure response was favorable in 37 patients, but failed to show any improvement in 14. The scintigraphic test was positive in 33 patients (15 cured, 17 improved, 1 failed) and negative in 18 (3 cured, 2 improved, 13 failed). Sensitivity and specificity for renovascular hypertension was 86.5% and 93%, respectively. For blood pressure cure and improvement, the test had positive and negative predictive values of 97% and 72%, respectively. A positive preoperative captopril renal scintigraphic result is a strong predictor of hypertension curability by renal artery revascularization.

[Percutaneous nephrostomy in neoplasm patients: when?]

The management of cancer patients with a lesion in its end stage is a clinical problem a satisfactory solution to which has not been found yet, because of the ethical and legal problems involved. The authors analyzed the survival rates of 218 patients with advanced neoplastic disease and obstructive renal failure who had undergone external/internal urinary diversion. One month after the procedure 20% of the patients were dead. The figure rose to 75% at 6 months and reached 98% at one year. Urinary diversion in cancer patients with renal failure is aimed not only at avoiding death and assuring a prolonged survival, but also at providing a good quality of life. Several clinical criteria are therefore analyzed which are used in the selection of patients to submit to nephrostomy. The most important factors seem to be the actual stage of the tumor, its primary location, the possibility of an effective antineoplastic therapy, and the patient's consent. Randomized long-term studies are still necessary to analyze not only survival rates but also quality of life after urinary diversion for obstructive renal failure.

[Duplex and Doppler color echocardiography for the study of renovascular hypertension. Comparison with arteriography]

Doppler US was employed to examine 46 patients with suspected renovascular hypertension (RVI) to detect stenosis/occlusion of the renal artery. In 25 cases duplex-Doppler technique was used, in 19 color-Doppler US, and 2 patients were examined with both methods. Doppler US was always performed before angiography which was considered as the reference gold standard. Using duplex-Doppler US, the diagnosis of renal artery stenosis was based on qualitative (spectral analysis of the waveform and absence of flow signal in cases of renal artery occlusion), and semiquantitative parameters (resistive index). Diagnostic accuracy of duplex US--which was compared with that of angiography--was 83%, its sensitivity was 91.6%, and specificity was 85%. With color-Doppler, two additional quantitative parameters were used (peak systolic frequency shift at the stenosis and stenosis index). In this group of patients sensitivity was 70%, specificity was 100%, and accuracy 85%. The good diagnostic yield of the method is counter-balanced by some limitations--e.g., operator dependence and long examination time (30-40 minutes, especially with duplex US). In the authors' opinion, Doppler technique can be used in the diagnosis of RVI, even though further study is necessary to exactly define diagnostic parameters, and to verify reproducibility and both inter- and intra-observer repeatibility. Technological progress may in the future reduce both difficulty and time of the examination.

Use of technetium-99m-MAG3 for renal scintigraphy after angiotensin-converting enzyme inhibition

Technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) was tested in 82 hypertensive patients submitted to renal scintigraphy 1 hr after oral premedication with 50 mg of Captopril. Baseline studies were obtained only for those patients showing abnormal findings in the provocative study. All patients underwent renal arteriography. Sensitivity and specificity for the detection of renal artery stenosis (RAS) greater than 50% were 89% and 91%, respectively. After Captopril administration, tracer parenchymal transit time increased significantly in ischemic kidneys (334 +/- 93 sec in baseline conditions versus 468 +/- 96 sec after Captopril, p less than 0.001) but not in kidneys with no RAS or RAS less than 50% (243 +/- 46 sec versus 271 +/- 95 sec, p = ns). False-positive responses were mostly bilateral and associated with a marked decrease in blood pressure. Technetium-99m-MAG3 is an effective compound for detecting RAS greater than or equal to 50% with Captopril renal scintigraphy. Performing the provocative test as a first step considerably reduced the number of scintigraphic studies required.

Evaluation of hypertensive patients by means of captopril enhanced renal scintigraphy with technetium-99m DTPA

One-hundred five hypertensive patients underwent conventional renal scintigraphy followed 2 or 3 days later by Captopril-enhanced renal scintigraphy, performed 1 hr after premedication with 50 mg of Captopril per os. All patients were then submitted to renal arteriography, performed within 15-30 days. Fifty-five patients had no renal artery stenosis, 29 had unilateral disease, and 21 bilateral. Overall, 34/37 patients were diagnosed by the provocative test as having at least one renal artery affected by a stenosis greater than 50%. Of those with no stenosis (n = 55) or stenosis less than 50% (n = 13) only two cases were falsely positive. Thus sensitivity was 92% and specificity 97%. For single kidney identification with stenosis greater than 50%, sensitivity of renal scintigraphy after Captopril administration was 94% and specificity 98%. Captopril enhanced renal scintigraphy is thus suggested as the first test to be performed in hypertensive patients referred for renal scintigraphic studies. Only those cases with equivocal results require a baseline study for better assessment.

[Angiographic study of the complications of vascular access in patients under hemodialysis]

Periodic hemodialysis requires the vascular access to be capable of functioning perfectly for a long time; therefore early diagnosis of the most common complications is very important. Fifty-four patients in dialysis treatment for end-stage renal failure (ESRF) were examined over a six-year period for vascular access (VA) complications. Eighty vascular accesses were studied: 68 arteriovenous fistulas and 12 arteriovenous grafts. The most frequent radiological investigation was phlebography, followed by arteriography by direct puncture of the humeral artery, and, in few cases only, by arteriography through femoral approach; the total number of radiographic examinations performed was 101. The most frequent complications were thromboses (50%) and stenoses (21%); aneurysms, pseudoaneurysms and radial artery steals were observed in 11% of the cases. Findings prove complications to depend neither on the type of VA (fistula, prosthesis) nor on its site (proximal, distal). In 50% of the cases angiography allowed a therapy to be adopted for VA recovery. Percutaneous transluminal angioplasty (PTA), performed on 3 patients, failed. Thus, in the authors' opinion, angiography is the method of choice for the evaluation of VA pathology, and surgery is the most efficient treatment for complications. Despite failures, PTA represents a valid alternative in the treatment of stenoses in larger vessels and prostheses.

[Diverticula of the female urethra. A radiological and ultrasound study]

The authors analyzed the clinical, radiographic and sonographic findings of diverticulum of the female urethra, reporting on 47 cases. Lower urinary tract infections, urgency and post-urinary dribbling were the most common symptoms. Either voiding cystourethrography or positive pressure urethrography was carried out in all patients, while US was performed in 18 cases only. Radiographs showed diverticula to be usually solitary (87%); their size ranged from 1 to 3 cm (72%). They were most commonly found in the mid-third of the urethra (83%), and stones were present in 12.7% of patients. Suprapubic and transrectal US demonstrated cystic lesions, usually dyshomogeneous, located under the bladder base and the uterine cervix. The authors believe that both examinations should be performed, as they provide with complementary information. X-ray study allows the evaluation of the exact number and position of diverticula, while US demonstrates both the extension of inflammatory changes and the size of diverticula not completely filled during voiding cystourethrography.

[Syringocele or cystic diagnosis of Cowper's gland ducts]

Cystic dilatation of bulbo-urethral gland ducts (Cowper's syringocele) is an uncommon abnormality, frequently asymptomatic, showing various radiographic patterns. The lesion is more commonly seen in children, but it may be found in adults too, and may cause dysuria, pollakiuria, stranguria and posturinary dribbling. Fourteen patients with syringocele were observed: 6 of them were asymptomatic, while in 8 the most common symptoms were posturinary dribbling and stranguria. X-ray examination showed 7 cases of perforated syringocele, 4 cases of ruptured syringocele, 2 cases of simple syringocele and 1 case of imperforate syringocele. Various theories are reported to explain how the lesion forms and the differences are analyzed which characterize different kinds of urethral lesions.

[Percutaneous transluminal dilatation of benign ureteral stenoses]

Ten benign ureteral strictures, in nine patients, were dilated with balloon catheter in conjunction with percutaneous nephrostomy. One patient had bilateral stenosis. The strictures followed ureteroileostomy (3 cases), uretero-uretero anastomosis (2 cases), ureteroneocystostomy (1 case), radical hysterectomy with associated ureteral fistula (1 case), post-surgical ureteral fistula (1 case) and benign long-standing stricture of unknown origin (1 case). Nine out of ten strictures were successfully dilated with disappearance of hydronephrosis. One patient underwent surgical correction of the stenosis. Dilation proved to be unsuccessful. The follow-up goes from 2 to 30 months and there is no evidence of obstruction.

[Percutaneous nephropyelolithotomy]

The fact that one can perform a wide passage through the kidney percutaneously with the subsequent introduction of a 26 F nephroscope has radically changed the technique used to remove kidney stones. They may either be extracted directly with forceps or following ultrasonic lithotripsy. The authors report their experience of 39 cases, in 32 of which the method was successful, 3 complications have been reported. The advantages of this method, both for the patient and for the community, are discussed in comparison to the surgical pielolithotomy. The problems concerning the dose absorbed by the operator are also examined.

Renal scintigraphy versus renal vein renin activity for identifying and treating renovascular hypertension

This paper compares renal scintigraphy (RS) with renal vein renin activity (RVRA), intravenous pyelography (IVP), and peripheral plasma renin activity (pPRA) in a population of hypertensive subjects with suspect renovascular hypertension (RVH), of whom 30 underwent surgery, in order to evaluate (a) screening ability of RS for RVH, and (b) surgical prognosis of RS for RVH. RS agreed with arteriographic findings of arterial stenosis in 91% of patients and proved more sensitive as a screening test than IVP and pPRA. The false-negative rate of RS was 9% and the false-positive rate was 10%. In the patients who underwent surgery RS was positive in 89% and RVRA in 85% of those who benefited from surgery. In this series false-negatives for RS occurred only in the presence of extensive collateral circulation, where RVRA also gave the same result. In patients who had been operated on, the sensitivity and specificity of RS, compared to RVRA, were very high. Our work supports the view that RS is a good screening test in RVH; moreover, it seems to be as accurate as RVRA as a surgical prognostic method for curable RVH.

[Echographic and urographic considerations in a case of lymphocele after renal transplantation (author's transl)]

Ultrasonography and urography are the most useful methods for the diagnosis of an uncommon complication or renal transplantation: the pararenal lymphocele. It presents on ultrasound as a well-defined sonolucent area adjacent to the renal transplant and must be differentiated from abscess, hematoma and urinoma.

[Radiological study of the hand of patients undergoing periodic hemodialysis. Possibilities and limitations of the method as an index of the evolution of the uremic disease]

The periodic X-ray examination of the hand in 50 patients in hemodialysis shows a good correlation between the radiologic findings and bone bioptic patterns. The method had instead a lesser interest in following the evolution of vascular and metastatic calcification.