Hans Scholz

Experimental study of hemodynamics in procedures to treat access-related ischemia

OBJECTIVE This experimental study investigated the hemodynamic effect of corrective procedures for arteriovenous access-related ischemia in pulsatile flow. METHODS Silicone models of an emulated tapered and bifurcated arterial tree of the upper arm and forearm were integrated into a pulsatile flow circuit. The model allowed the study of hemodynamics of simulated arteriovenous fistulas, including collateral circulation, as well as the study of different simulated procedures to improve distal hypoperfusion. Flow rates and arterial pressure were measured simultaneously during simulation of corrective procedures and correlated to hemodynamic values of uncorrected ischemia. RESULTS It was demonstrated that the more proximally localized an arteriovenous anastomosis is, the higher the distal arterial pressure will be at any given fistula flow. Reduction of the fistula flow resulted in a significant improvement of distal perfusion. Ligation of the artery distal to the arteriovenous fistula to prevent retrograde flow increased the distal perfusion only slightly in simulated ischemia. In contrast, the simulated corrective procedures of distal revascularization interval ligation and proximalization of arterial inflow resulted in a significant improvement. The most significant improvement of distal perfusion was observed with the simulated proximalization technique, whereas the effect of distal revascularization technique was less pronounced at higher fistula flow. Arterial ligation after distal revascularization increased the distal pressure only by 10%. CONCLUSION A more centrally localized arteriovenous anastomosis and a reduction of fistula flow significantly increase distal perfusion. The procedure of proximalization of arterial inflow is at least equivalent to the distal revascularization interval ligation technique for the correction of distal ischemia, but does not sacrifice a patent axial artery. The moderate effect of interval ligation of the latter technique should be evaluated by further intraoperative measurements.

A new method of intraoperative hydraulic impedance measurement provides valuable prognostic information about infrainguinal graft patency

PURPOSE Prognostic information about graft outcome, obtained by using a new method for intraoperative measurement of vascular impedance, was evaluated. METHODS Hydraulic impedance was measured in 136 infrainguinal bypass grafts that were entered into a multicenter trial. Seventy femoropopliteal and 66 femorocrural polytetrafluoroethylene (PTFE) grafts were used. The arterial impedance measurement involved a silicon bypass graft temporarily inserted between the proximal and distal anastomoses sites. A flowmeter probe and a pressure transducer were incorporated into the tube. The digitally stored waveforms were subjected to a fast Fourier transformation and both input (Z(x)) and characteristic (Z(0)) impedances, as well as phase relations, were computed and related to graft outcome after 3 years. RESULTS Significant prognostic information for both popliteal and crural grafts was provided by means of the phase angle of the first harmonic. Primary and secondary patency rates for popliteal bypasses were 45% +/- 1% and 65% +/- 2% for phase angles greater than -40 degrees (n = 57) and 37% +/- 1% and 40% +/- 1% for phase angles less than -40 degrees (n = 13, p(prim ) = not significant, p(sec) < 0.01). For crural grafts, the secondary patency rates were 49% +/- 1% and 61% +/- 2% for phase angles greater than -40 degrees (n = 53) and 15% +/- 1% and 0% for phase angles less than -40 degrees (n = 13, P <.01). All crural bypass grafts with phase angles less than -40 degrees occluded within 16 months. Steady flow resistance, as well as Z(x) and Z(0), failed to indicate a significant relation to graft prognosis. CONCLUSION This method provides reliable prognostic information regarding graft patency and opens hydraulic impedance measurement to clinical surgery. The phase lag between flow and pressure curves, as expressed by the phase angle of the first harmonic, provides significant prognostic information.

Treatment of Perigraft Seroma in Expanded Polytetrafluoroethylene Grafts by Sequential Fibrin Sealing of the Outer Graft Surface

BACKGROUND The recommended standard for treatment of perigraft seroma (PS) is the graft removal and the reconstruction using an alternative prosthesis. We assumed that a fibrin sealing of the outer surface of expanded polytetrafluoroethylene (ePTFE) grafts would prevent leakage and used this technique in the treatment and prevention of PS. METHODS Over a 10-year period, 24 patients were treated for PS after subcutaneous implantation of ePTFE grafts (14 arterial bypasses and 10 arteriovenous grafts). Affected graft segments were temporarily removed and underwent sequential fibrin sealing technique before reimplantation. In addition, an in vitro experiment was carried out to demonstrate the efficacy of fibrin sealing to prevent leakage through the ePTFE graft wall, after its hydrophobic barrier was destroyed by filling with saline solution under pressure. RESULTS A cure of PS was observed in 20 patients (84%) at a follow-up period of 37 ± 18 months. A later graft infection was not seen in any patient. The patency rate of reconstructed grafts appears to be unaffected. In the performed experiment we have demonstrated an elimination of leakage through the graft wall by the fibrin sealing technique. CONCLUSIONS Sequential fibrin sealing of the outer surface is an effective way to treat PS in ePTFE grafts. However, failure of this treatment cannot be precluded. Further studies are necessary that may provide further insights into the causes and best treatment of PS and the possibly important role of PS in the aneurysm enlargement after complete endovascular exclusion with ePTFE endografts.

Das arterioarterielle Interponat als Dialysezugang

Zusammenfassung Bei 2 Patienten bestand nach Ausnutzung der subcutanen Venen sowie verschiedener Möglichkeiten a.v.-Interponate erneut der Bedarf eines Dialysezugangs. Es erfolgte die Anlage eines arterioarteriellen Interponats (PTFE) als Schlinge am Oberschenkel zwischen der A. femoralis communis und der A. profunda femoris bzw. A. femoralis superficialis. Beide Patienten wurden postoperativ antikoaguliert. Das Interponat im Bereich der A. femoralis superficialis funktioniert neun Monate nach Anlage unproblematisch. Bei dem Interponat zur A. profunda femoris kam es wiederholt zum Verschluß, so daß nach 6 Monaten an der gleichen Extremität ein neues Interponat terminoterminal im Bereich der A. femoralis communis angelegt wurde. Diese neue Interponat wird fünf Monate nach Anlage problemlos für die Dialyse genutzt. Arterioarterielle Protheseninterpositionen als Dialysezugänge können somit bei nicht geeigneter venöser Abflußbahn für die chronische Dialyse genutzt werden.Abstract We report on two patients who received arterio-arterial PTFE grafts as vascular access for chronic hemodialysis. In both patients prior surgery for arteriovenous fistulas using either subcutaneous veins or arteriovenous, artificial PTFE grafts had failed due to recurrent thrombosis and septic complications. The arterio-arterial grafts were each positioned as a subcutaneous loop on the thigh and anastomosed with the common femoral artery and the superficial femoral artery or the profunda femoris, respectively. Postoperatively, both patients received coumadine for anticoagulation. Nine months after surgery no complications were observed in the former patient. The latter patient experienced recurrent thrombotic occlusion of the graft and a new graft was required which was anastomosed end-by-end onto the common femoral artery. As yet, 5 months after the second operation, no further complications have been reported. In conclusion, in patients lacking suitable veins for arterio-venous anastomoses, artificial arterio-arterial grafts may provide vascular access for chronic hemodialysis.

Experimentelle Optimierung der Haemodynamik distaler termino-lateraler Bypass-Anastomosen, Entwicklung einer neuen Anastomosenform

Die subendotheliale Intimahyperplasie (IH) stellt eine der Hauptursachen fur die Ausbildung von Stenosen im Bereich von Anastomosen dar [1, 6]. Besondere Bedeutung hat die IH in termino-lateralen Anastomosen. Fur die Entstehung der IH sind neben anderen Faktoren, wie etwa dem sogenannten compliance mismatch, haemodynamische Ursachen wahrscheinlich, die wesentlich durch die Geometrie des Anastomosenbereiches bestimmt werden [2, 4, 5, 7]. Die klinische Bedeutung der IH wachst mit abnehmendem Gefasdurchmesser. So sind Spatverschlusse von femoro-infragenualen Bypassen, und besonders bei cruraler distaler Anastomose, am wahrscheinlichsten durch die Ausbildung der IH zu erklaren.

Principles of infragenicular vascular reconstruction in patients with critical limb ischemia

Between January 1, 1989 and April 26, 1994, in the Clinic of Vascular Surgery of Humboldt-Universitat Berlin (Charite), 318 infragenicular reconstructions in patients with critical limb-ischemia at stages III and IV were performed. The special diagnostic management, bypass reconstruction with reference to placement of the graft, choice of bypass material, problems of distal anastomosis, specialities of the Femor-Crural-Patch-Prosthesis (FCPP), the intraoperative measurement of peripheral resistance, and control of the bypasss-flow by duplex scanning are described. data, but a prognostic trend analysis is possible.

Indikationen, Technik und klinische Ergebnisse der Revaskularisation von A. mesenterica inferior und A. iliaca interna bei Rekonstruktionen im aortofemoralen Bereich

Eingriffe im aortofemoralen Bereich gehoren zu den haufigsten gefaschirurgischen Operationen. Sowohl bei der Rekonstruktion obstruktiver als auch aneurysmatischer Veranderungen kann es zu einer Beeintrachtigung des Einstromes in die A. mesenterica inferior, die Aa. iliacae internae, die Lumbalarterien und die kleineren Aste der A. femoralis comm kommen Ernste, haufig todlich verlaufende Komplikationen der resultierenden Minderperfusion sind relativ selten und entziehen sich damit der personlichen Erfahrung eines Teiles der Chirurgen. Daraus resultiert die sehr unterschiedliche, teilweise kontrare Einstellung zur Revaskularisation der A. mesenterica inferior und A. iliaca interna bei Rekonstruktionen im aorto-femoralen Bereich, die von „kaum einmal notig“ bis zu „sollte immer erfolgen“ reicht. Das Ziel der vorliegenden Arbeit ist die Darstellung dieser Problematik auf der Grundlage des Schrifttums, des eigenen Patientenguts und pathophysiologischer Untersuchungen.