Biomedical subjects

Hans Scholz

Publications and source records attributed to Hans Scholz.

6 recordsLinked to original sources

PubMed2006

Proximalization of the arterial inflow: a new technique to treat access-related ischemia.

OBJECTIVE: Arteriovenous access-related ischemia is an uncommon but serious and occasionally devastating complication. Distal revascularization-interval ligation (DRIL) has been established as a standard treatment procedure; however, an axial artery is ligated and the distal perfusion is maintained by the construction of an arterial bypass. Because such an approach, in principle, appears undesirable, we developed and applied an alternative technique referred to as proximalization of the arterial inflow (PAI). This procedure converts the arterial supply of the arteriovenous access to a more proximal artery with higher capacity by using a small-caliber polytetrafluoroethylene graft as a feeder. METHODS: From January 1999 to June 2005, the PAI technique was applied in 30 patients. The indication was seen in patients with severe distal ischemia who had a flow volume rate of <800 mL/min in a native fistula and <1000 mL/min in prosthetic access. RESULTS: Pain was the dominant symptom of ischemia in most patients before surgery. In 37%, a tissue loss was observed. The symptoms of access-related ischemia disappeared completely in 84% of patients and improved significantly in 16%. The significant hemodynamic improvement was confirmed by an increase of the intraoperatively measured mean distal arterial pressure from 32 +/- 9 mm Hg to 63 +/- 8 mm Hg. The digital-brachial index increased from 0.40 +/- 0.10 to 0.83 +/- 0.07. The mean access flow rate was 658 +/- 80 mL/min after PAI and did not differ significantly with the preoperative value (634 +/- 181 mL/min). With a mean follow-up interval of 26.1 +/-19.1 months, the primary and secondary patency rates were, respectively, 87% and 90% at 1 year and 67% and 78% at 3 years. CONCLUSIONS: The PAI procedure represents a well-suited alternative to the DRIL technique for the treatment of patients who develop ischemia after creation of an arteriovenous access. Results for access salvage and disappearance of ischemic symptoms are equivalent to the DRIL technique. In contrast to the DRIL procedure, the PAI technique preserves the natural arterial pathway. Hence, PAI is preferable for surgeons who are reluctant to ligate an axial artery and are concerned about potentially disastrous consequences.

Aged↗

PubMed2006

Flow reduction in high-flow arteriovenous access using intraoperative flow monitoring.

PURPOSE: This study used intraoperative monitoring of the access flow to evaluate the results of flow reduction in the management of high-flow arteriovenous access-related symptoms of distal ischemia and cardiac insufficiency. METHODS: A retrospective study was conducted of 95 patients (78 with ischemia, 17 with cardiac failure) who underwent flow reduction between 1999 and 2005. A preoperatively measured access flow-volume rate > 800 mL/min for autogenous accesses (n = 77) and > 1200 mL/min for prosthetic accesses (n = 18) was the selection criterion for the use of a flow reduction procedure. Flow reduction was achieved using a spindle-like narrowing suture near the anastomosis and final placement of a polytetrafluoroethylene strip while a flow meter was used for intraoperatively measuring the access flow. The desired postoperative flow was 400 mL/min for autogenous and 600 mL/min for prosthetic accesses. RESULTS: The mean preoperative access flow was 1469 +/- 633 mL/min in patients with ischemia and 2084 +/- 463 mL/min in patients with cardiac failure, without significant differences between access types. The flow was reduced to 499 +/- 175 mL/min for autogenous accesses and to 676 +/- 47 mL/min for prosthetic accesses. The mean follow-up was 25 months (range, 1 to 73 months). Complete long-term relief of symptoms was observed in 86% of patients with ischemia and in 96% of patients with cardiac failure. Reconstruction significantly increased the digital-brachial index (0.41 +/- 0.12 vs 0.74 +/- 0.11; P < .05) and mean distal arterial pressure (47 +/- 17 mm Hg vs 79 +/- 21 mm Hg; P < .05) in patients with ischemia. Primary patency rates were significantly better for reconstructed autogenous accesses compared with rates of prosthetic accesses (91% +/- 4% vs 58% +/- 12% at 12 months; 81% +/- 6% vs 41% +/- 14% at 36 months; P < .001). The low patency of reconstructed prosthetic accesses is due to the high thrombosis risk of accesses that have a flow < 700 mL/min. CONCLUSIONS: Flow reduction using intraoperative access flow monitoring is an effective and durable technique allowing for the correction of distal ischemia and cardiac insufficiency in patients with a high-flow autogenous access. The desired postoperative access flow of 400 mL/min is not associated with an increased risk of thrombosis. Flow reduction of prosthetic access is as effective; however, a higher access flow than the desired 600 mL/min seems to be necessary to achieve an acceptable patency in prosthetic accesses.

Arteries↗

PubMed2005

Arterioarterial prosthetic loop: a new approach for hemodialysis access.

OBJECTIVES: In this report we present a novel procedure that uses an arterioarterial prosthetic loop (AAPL) with the proximal axillary or the femoral artery as a vascular access for hemodialysis in patients who have inadequate vascular conditions for creating an arteriovenous fistula or graft. METHODS: Between April 1996 and September 2004, 34 patients received 36 AAPLs as vascular access, either as an axillary chest loop (n = 31) or as a femoral loop (n = 5). In this procedure the artery is ligated between the anastomoses to direct flow through the AAPL. Data from all patients undergoing the procedure were prospectively collected. RESULTS: The indication for an AAPL was the unsuitability of large deep veins in 64%, steal syndrome in 11%, the combination of only a suitable femoral vein and severe peripheral arterial disease in 22%, and congestive heart failure in 3%. All AAPLs were cannulated 18 +/- 4 days postoperatively. Mean follow-up was 31 months (range, 1 to 83). Primary patency was 73% and secondary patency was 96% at 1 year; these rates at 3 years were 54% and 87%, respectively. The rate of all interventions for the maintenance of AAPL function was 0.47 procedures per patient year. Four grafts were abandoned. More than 11,000 hemodialyses with proven efficiency were performed. CONCLUSIONS: The AAPL is an unusual but useful and easy-to-perform alternative procedure to create vascular access for hemodialysis. It can provide survival for strictly selected patients in whom conventional vascular access is not possible. The axillary chest AAPL is preferred.

Arteriovenous Shunt, Surgical↗

PubMed2004

Effect of tapered grafts on hemodynamics and flow rate in dialysis access grafts.

AIM: Aside from the high incidence of venous stenosis, high-output failure and peripheral steal syndromes remain serious problems of vascular access. Meanwhile commercial tapered grafts are available to address this topic, but little is known about its effect neither on graft flow nor on hemodynamics. METHODS: Anastomotic models were constructed using a clear silicon elastomer. The arterial anastomosis was shaped in two ways: 1) like a direct connection of artery and 7-mm graft and 2) with a 4-mm diameter segment between artery and graft. Hemodynamic measurements were performed in a pulsatile flow circuit to simulate blood flow at physiological conditions. Flow patterns were obtained by direct dye injection. Additionally, the correlation between the length of narrow segment and mean arterial pressure was investigated. RESULTS: In all models using a 4-mm segment, the oscillating anastomotic vortex was disappeared. This vortex was shifted to the area behind the well-rounded expansions of the graft demonstrating a new separation region, but the flow direction was constant during the whole simulated cycle. At identical pressure rates and waveforms the length of narrow segment determined the graft flow rate directly (e.g., at mean pressure 100 mmHg, flow reduction up to 28% in 4-mm segments, and up to 55% in 3-mm segments). CONCLUSION: These findings indicate that taper is an important consideration in the design of vascular access grafts.

Arteriovenous Shunt, Surgical↗

PubMed2003

Correlation between angiographic runoff and intraoperative hydraulic impedance with regard to graft patency.

The aim of this study was to evaluate the correlation between peripheral runoff estimated by the SVS/ISCVS scoring system and intraoperatively measured outflow. Sixty-six patients received 27 femoropopliteal and 39 femorocrural ePTFE grafts. During the operation, peripheral resistance and hydraulic impedance were measured by means of the extracorporeal-bypass-flow method. Angiographic runoff was estimated according to the revised SVS/ISCVS system. Patients were entered in a graft surveillance program and patency was calculated after 3 years. The relation between the angiographic runoff score and graft patency as well as correlations between hemodynamic data, peripheral resistance, and hydraulic impedance were calculated. Primary and secondary patency rates for femoropopliteal grafts were 44% and 60% and those for femorocrural bypasses were 35% and 45%. Mean angiographic vessel diameters for above-knee and below-knee popliteal arteries were 0.51 +/- 0.02 mm and 0.47 +/- 0.04 mm. Diameters of crural arteries were 0.34 +/- 0.03 mm (posterior tibial artery), 0.27 +/- 0.02 mm (anterior tibial artery) and 0.26 +/- 0.21 mm (peroneal artery). The differences in diameter between popliteal and crural grafts were statistically significant ( p < 0.01). Calculated correlations between the preoperative score and hemodynamic, resistance, and impedance values or patency rates were generally poor and statistically not significant. A statistical significant correlation was found only between SVS/ISCVS score and recipient vessel diameters. The angiographic runoff did not correlate with peripheral resistance, impedance, or patency rates. Patients with angiographically poor outflow should additionally be evaluated with duplex sonography or magnetic resonance angiography and should not be denied peripheral reconstructions.

Adult↗

PubMed2002

Computational fluid dynamics and vascular access.

Anastomotic intimal hyperplasia caused by unphysiological hemodynamics is generally accepted as a reason for dialysis access graft occlusion. Optimizing the venous anastomosis can improve the patency rate of arteriovenous grafts. The purpose of this study was to examine, evaluate, and characterize the local hemodynamics and, in particular, the wall shear stresses in conventional venous end-to-side anastomosis and in patch form anastomosis (Venaflo) by three-dimensional computational fluid dynamics (CFD). We investigated the conventional form of end-to-side anastomosis and a new patch form by numerical simulation of blood flow. The numerical simulation was done with a finite volume-based algorithm. The anastomotic forms were constructed with usual size and fixed walls. Subdividing the flow domain into multiple control volumes solved the fundamental equations. The boundary conditions were identical for both forms. The velocity profile of the patch form is better than that for the conventional form. The region of high static pressure caused by flow stagnation is reduced on the vein floor. The anastomotic wall shear stress is decreased. The results of this study strongly support patch form use to reduce the incidence of intimal hyperplasia and venous anastomotic stenoses.

Algorithms↗