B. Marty

Alternatives to unfractioned heparin for anticoagulation in cardiopulmonary bypass

Despite the progress made in the development of cardiopulmonary bypass (CPB) equipment, systemic anticoagulation with unfractioned heparin and post-bypass neutralization with protamine are still used in most perfusion procedures. However, there are a number of situations where unfractioned heparin, protamine or both cannot be used for various reasons. Intolerance of protamine can be addressed with extracorporeal heparin removal devices, perfusion with (no) low systemic heparinization and, to some degree, by perfusion with alternative anticoagulants. Various alternative anticoagulation regimens have been used in cases of intolerance to unfractioned heparin, including extreme hemodilution, low molecular weight heparins, danaparoid, ancrod, r-hirudin, abciximab, tirofiban, argatoban and others. In the presence of heparin-induced thrombocytopenia (HIT) and thrombosis, the use of r-hirudin appears to be an acceptable solution which has been well studied. The main issue with r-hirudin is the difficulty in monitoring its activity during CPB, despite the fact that ecarin coagulation time assessment is now available. A more recent approach is based on selective blockage of platelet aggregation by means of monoclonal antibodies directed to GPIIb/IIIa receptors (abciximab) or the use of a GPIIb/IIIa inhibitor (tirofiban). An 80% blockage of the GPIIb/IIIa receptors and suppression of platelet aggregation to less than 20% allows the giving of unfractioned heparin and running CPB in a standard fashion despite HIT and thrombosis. Likewise, at the end of the procedure, unfractioned heparin is neutralized with protamine as usual and donor platelets are transfused if necessary. GPIIb/IIIa inhibitors are frequently used in interventional cardiology and, therefore, are available in most hospitals.

Active cooling during open repair of thoraco-abdominal aortic aneurysms improves outcome.

OBJECTIVE Evaluate impact of active cooling with partial cardiopulmonary bypass (CPB) and low systemic heparinization during open repair of thoracoabdoninal aortic aneurysms. METHODS Prospective analysis of 100 consecutive patients undergoing surgical repair of thoracoabdominal aortic aneurysms. Partial CPB and normothermic (36 degrees C) or hypothermic (29 degrees C) perfusion was selected in accordance to the surgeons preference. In the hypothermic group, aortic cross clamp was applied when the target temperature of the venous blood was achieved and rewarming was started after declamping. RESULTS 52/100 patients (62.2+/-10.9 years) received normothermic and 48/100 patients hypothermic perfusion (63.8+/-10.6 years: NS). Emergent procedures accounted for 18/52 (35%) with normothermia vs. 21/48 (44%: NS) with hypothermia. The number of aortic segments (eight = maximum including arch and bifurcation) replaced was 3.9+/-1.5 with normothermia vs. 4.1+/-1.5 with hypothermia (NS); Crawford type II aneurysms accounted for 21/52 patients (40%) for normothermia vs. 20/48 (42%:NS) for hypothermia. Total clamp time was 38+/-21 min with normothermia vs. 47+/-28 min with hypothermia (P=0.05). Pump time was 55+/-28 min with normothermia vs. 84+/-34 min with hypothermia (P=0.001). Mortality at 30 days was 8/52 patients (15%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.06; odds ratio = 4.1). Parapareses/plegias occurred in 4/52 patients (8%) with normothermia vs. 4/48 (8%) with hypothermia (NS). Revisions for bleeding were required in 4/52 patients (8%) with normothermia vs. 2/48 patients (4%) with hypothermia (P=0.38). Revisions for distal vascular problems were necessary in 5/52 patients (10%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.25). Freedom from death, paraplegia, and surgical revision was 89.9% with normothermia vs. 94.8% with hypothermia (P=0.04; odds ratio 2.0). CONCLUSIONS Active cooling during repair of thoracoabdominal aortic aneurysms allows for longer cross-clamp times, more complex repairs and improves outcome.

Biologic Fixation of Polyester-versus Polyurethane-covered Stents in a Porcine Model

PURPOSE Migration of endoprostheses remains a concern in endovascular aneurysm treatment. Biologic fixation is supposed to enhance anchorage, but the diseased atherosclerotic aorta in humans has demonstrated a limited capacity to incorporate an endoprosthesis by cellular proliferation. The biologic response of two different types of endoprostheses was evaluated in the porcine aorta. MATERIALS AND METHODS Two types of endoprostheses--four polyurethane-covered (PUC) stents with a macroporous polyurethane covering and four polyester-covered (PEC) stents with a woven polyester covering--were implanted in eight infrarenal porcine aortas for 6 weeks. Electron microscopy and qualitative and quantitative microscopy were performed on serial cross sections. RESULTS The PUC stents demonstrated an increase in diameter (from 8 mm +/- 1 to 10 mm +/- 1, 12.5%; P = .009), whereas the PEC stents persisted in their original dimensions (8 mm +/- 1, 0%). PUC and PEC stents were covered by continuous thrombus-free neointima (269 microm +/- 51 vs 575 microm +/- 113, respectively; P < .01). The PUC stents demonstrated firm attachment to the aorta as a consequence of a granulation tissue with ingrowth into the pores of the polyurethane covering. The PEC stents remained in loose contact with the aorta in the absence of tissue ingrowth. CONCLUSIONS Enhanced biologic fixation was achieved by extensive granulation tissue invading the pores of PUC endoprostheses. This finding can modify the design of future devices.

Benefits of Endoscopic Vein Harvesting

The purpose of this study was to evaluate and compare the benefits of endoscopic saphenous vein harvesting (EVH) with the traditional incision technique (TIT) for coronary artery bypass grafting (CABG) in respect to the technical procedure and clinical outcome. In a prospective nonrandomized, case-matched study the greater saphenous vein was harvested for CABG in 22 patients using the endoscopic technique and in 18 patients with the traditional method. Comparisons were made for the operating time, length of incision and vein harvested, graft quality, postoperative complications, and pain assessment. Patient demographics were well matched. EVH required smaller incisions than did the TIT (10.5 ± 6.6 vs. 31.2 ± 7.8 cm, respectively; p < 0.0001). Harvest time and vein quality were comparable in the two groups. Total vein operating time was shorter following the endoscopic technique (60 ± 24 vs. 100 ± 35 minutes, respectively; p < 0.0001). EVH had fewer complications (NS), and postoperative pain was significantly less (p= 0.0034). The major advantages of endoscopic vein harvesting are a significant reduction of postoperative pain and strikingly better cosmetic results. Wound complications seem to be less frequent.

A siliconized hollow fiber membrane oxygenator.

Most membrane oxygenators are built with microporous fibers known for plasma leakage in long-term use such as extracorporeal life support or extracorporeal membrane oxygenation. The current study was designed to evaluate the Quadrox oxygenator in which the fibers have been coated with silicone (Jostra). Six calves (mean weight, 62 +/- 4 kg) were connected to cardiopulmonary bypass (CPB) by jugular venous and carotid arterial cannulation, with a mean flow rate of 3 L/min for 6 hours. They were randomly assigned to a standard Quadrox oxygenator (standard group, n = 3) or a siliconized Quadrox oxygenator (silicone group, n = 3). After 7 days, the animals were sacrificed. A standard battery of blood samples was taken before bypass, after mixing for 10 minutes, and after 1, 2, 5, and 6 hours of perfusion. Analysis of variance was used for repeated measurements. Total oxygen transfer and carbon dioxide transfer did not differ between groups (p = 0.5 for comparison). Blood trauma, evaluated by plasma hemoglobin (Hb), did not detect any significant hemolysis in either group. Thrombocyte and white blood cell count profiles in both groups were parallel and without significant differences (p = 0.1 and 0.6, respectively). At the end of testing no clot deposition was found in the oxygenator. At postmortem, there were no signs of peripheral emboli. The results of this study suggest that this silicone coating of hollow fibers allows for good gas transfer, while preserving all the mechanical advantages of a conventional hollow fiber oxygenator.

Intravascular Gas Transfer: Membrane Surface Area and Sweeping Gas Flows Are of Prime Importance

Single and double hollow fiber intravascular gas exchangers were evaluated in an extracorporeal veno-venous bypass circuit (right atrium to pulmonary artery) including a tubular blood chamber (mimicking caval veins with an inner diameter of 26 mm) for evaluation of the membrane surface area/host vessel diameter gas transfer relationships. Six bovine experiments (body wt: 68 ± 4 kg) with staged ex vivo blood flows of 1, 2, 3, and 4 L/min and a device oxygen inflow of 0, 3, and 6 L/min (0 or 3 L/min/device) were performed. Total oxygen transfer at a blood flow of 1 L/min was 33 ± 4 ml/min for a gas flow of 3 L/min (one device) vs 60 ± 25 ml/min for a gas flow of 6 L/min (two devices); at a blood flow of 2 L/min, the corresponding oxygen transfer was 46 ± 16 ml/min for a gas flow of 3 L/min vs 95 ± 44 ml/min for a gas flow of 6 L/min; at a blood flow of 3 L/min, the corresponding oxygen transfer was 48 ± 24 ml/min for a gas flow of 3 L/min vs 92 ± 37 ml/min for a gas flow of 6 L/min (p < 0.01 for comparison of areas under the curves). Total carbon dioxide transfer at a blood flow of 1 L/min was 47 ± 18 ml/min for a gas flow of 3 L/min vs 104 ± 26 ml/min for a gas flow of 6 L/min; at a blood flow of 2 L/min, the corresponding carbon dioxide transfer was 59 ± 19 ml/min for a gas flow of 3 L/min vs 129 ± 39 ml/min for a gas flow of 6 L/min; at a blood flow of 3 L/min, the corresponding carbon dioxide transfer was 60 ± 22 ml/min for a gas flow of 3 L/min vs 116 ± 49 ml/min for a gas flow of 6 L/min (p < 0.01). For the given setup, the blood flow/gas transfer relationship is non linear, and a plateau is achieved at a blood flow of 2.5 L/min for O2 and CO2. Doubling membrane surface area and consecutively sweeping gas flows result in doubling of gas transfers at all tested blood flows. However, increased membrane surface area and blood flow produce a higher pressure drop that in turn limits the fiber density that can be used clinically.

Intravascular oxygenation. Influence of the host vessel diameter on oxygen transfer.

An extra corporeal venovenous bypass circuit (right atrium to pulmonary artery), including an intravascular gas exchanger in a blood chamber with a variable inner diameter, was developed for ex vivo evaluation of the host vessel diameter/intravascular oxygen transfer relationship. Three host vessel diameters mimicking different configurations of the caval axis were studied in three bovine experiments (body weight 82 ± 3 kg). Blood flow was 3,000 ml/min and device oxygen inflow was 2,300 ml/min. Serial blood samples were taken for 26 mm, 23 mm, and 20 mm inner blood chamber diameters after hemodynamic stabilization before and after exposure of the circulating blood to the intravascular gas exchanger (sampling ports at blood chamber inlet and outlet). Measured oxygen saturation at the blood chamber inlet was 25.0 ±11.7% for the 26 mm diameter as compared to 31.7 ± 12.6% for 23 mm, and 28.7 ± 9.2% for 20 mm. At the outlet, the corresponding O2 saturations were 34.5 ± 11.5% for 26 mm, 42.9 ± 8.8% for 23 mm, and 43.2 ± 6.2 for 20 mm. Total O2 transfer was 24.9 ± 11.5 ml/min for 26 mm, 31.9 ± 7.4 ml/min for 23 mm, and 35.9 ± 12.2 ml/min for 20 mm (p < 0.05). Likewise, O2 transfer rate was 8.3 + 3.8 ml/L, 10.6 + 2.4 ml/L, and 12.0 ± 4.0 ml/L (p < 0.05). Parallel analyses of total CO2 transfer and CO2 transfer rates provided less consistent findings. At 3 L/min, the pressure drop between the inlet and outlet of the blood chamber was 12 ± 3 mmHg for 26 mm, 26 ± 1 mmHg for 23 mm, and 38 + 2 mmHg for 20 mm diameters (p < 0.001). The authors conclude that oxygen transfer of a given intravascular gas exchanger appears to be indirectly proportional to the host vessel diameter. Increasing blood pressure gradient as a function of decreasing diameter has to be considered in clinical application.

Herz- und Gefässchirurgie: Die endovaskuläre Sanierung von Aortenaneurysmen setzt sich durch!

Seit Anfang der neunziger Jahre des letzten JahrhundertswirdanderendovaskulärenAneurysmasanierung mit Hilfe von kathetergängigen Endoprothesen (EVAR) [1] gearbeitet. Diese Prothesen sind blutdicht, sogenannte «covered stents». In der Regel werden dafür selbstexpandierende Stents aus Nitinol oder nichtrostendem Stahl eingesetzt, die mit einer Hülle aus Dacron® oder Polytetrafluorethylen versehen sind. Die Verankerung dieser Implantate in der Aorta und in ihren Ästen, diesund jenseits des zu sanierendenAneurysmas,geschiehtdurchgeeigneteÜberdimensionierung des Implantats (Reibungsfixation). Mit der Zeit haben sich die für diese Therapieform relevanten Fragestellungen von der Machbarkeit (Verbesserung der Einführungsbestecke), zur Verlässlichkeit (Verbesserung der Implantate, Nachkontrollen) und schliesslich zur potentiellen Gefährdung der Patienten wegen Nachoperationen einerseits und der Erweiterung der Indikationen andererseits verlagert. In unseren Händen hat sich die endovaskuläre Aneurysmasanierung zur Evaluation erster Wahl für die Routinebehandlung entwickelt. Dies gilt sowohl für elektive als auch für notfallmässige Eingriffe und wurde durch die Bereitstellung folgender Elemente ermöglicht: durch die gängigen geraden bzw. konischen Endoprothesen und Bifurkations-Endoprothesen im Operationstrakt; durch einen EVAR-Katheterwagen, ergänzt mit den nötigen Schleusen, Führungsdrähten, Ballonen usw. für die Einrichtung der spezifischen vaskulären Zugänge, sowie durch ein mobiles intravaskuläres Ultraschallgerät (IVUS) für die intraoperative Ausmessung der Aneurysmakonfiguration [2] und einen mobilen C-Bogen für die Durchleuchtung. Dadurch sind wir in der Lage, in jedem Operationssaal unseres Hauses, und in Kombination mit einem Lieferwagen auch ausser Haus, endovaskuläre Eingriffe mit Ausmessung in Echtzeit durchzuführen.