Recombinant human antithrombin prevents xenogenic activation of hemostasis in a model of pig-to-human kidney transplantation.

BACKGROUND: Xenogenic activation of hemostasis (XAH) represents a major hurdle for the transplantation of discordant animal organs into humans as it results in thrombotic microangiopathy (TMA). We have previously shown that recombinant human-activated protein C (rhAPC) mitigates XAH and TMA in an ex vivo model of pig-to-human kidney transplantation. However, the use of rhAPC may not be feasible in a perioperative setting due to possible bleeding complications. METHODS: Here, we explored the effects of another natural inhibitor of coagulation, human recombinant antithrombin (rhAT), in comparison with rhAPC. Unmodified porcine kidneys (n = 25) were perfused ex vivo with porcine blood, human blood, or human blood supplemented with rhAPC or rhAT. Surrogate parameters of organ survival, markers of XAH (D- Dimer, thrombin-antithrombin complex [TAT], fibrinogen, antithrombin activity, plasminogen), endothelial cell and platelet activation (E-selectin, P-selectin), platelet function tests and histological signs of TMA were evaluated. RESULTS: Perfusion was feasible for > 240 min in all experiments with autologous porcine blood, but limited to 126 ± 78 min with human blood due to increased vascular resistance. Addition of rhAT protected from TMA and allowed for perfusion times > 240 min. In addition, there were less signs of XAH with reduced release of P-selectin and overexpression of E-selectin, whereas the progressive loss of platelet function, observed during discordant perfusion, was prevented. The effect of rhAT was dose-dependent with maximum protection obtained at 3 IU/ml. CONCLUSION: In conclusion, in this ex vivo model of discordant xenotransplantation, rhAT reduced XAH and prevented TMA in doses that appear feasible for use in clinical or preclinical transplantation settings.

On the use of unsealed polypropylene mesh as tracheal replacement.

The necessity of a cervical tracheal replacement arises with thyroid carcinoma, which occasionally infiltrates the trachea extensively, the rare primary tracheal tumors and, sporadically, benign stenoses. In the present study, we used an uncoated porous polypropylene prosthesis as cervical tracheal replacement in sheep. Specifically, we implanted a tracheal prosthesis of polypropylene mesh as a cervical tracheal replacement in five sheep, protecting the airways with self-expanding stents. Healing-in of the prostheses was checked bronchoscopically. The animals were killed after increasing survival times (7, 28, 64, 68, and >90 days), and incorporation of the prosthesis was examined macroscopically, microangiographically and histologically. Although medium-term survival was possible with a sufficiently wide airway, all animals were ultimately euthanized because of complications (airway stenosis, prolapse of prosthesis). Nevertheless, the results show that replacement of the cervical trachea with a polypropylene mesh can be successful under different experimental conditions.

Resistance to pressure of the stump after mechanical stapling or manual suture. An experimental study on sheep main bronchus.

OBJECTIVE: In a previous experimental study on 60 freshly slaughtered pig trachea, a statistically significant better resistance to pressure was found after mechanical stapling compared to hand suture. The objective of this study was to determine the resistance to pressure of a bronchial stump depending upon the closure technique (manual vs. mechanical) used in sheep 14 days after pneumonectomy. METHODS: Pneumonectomy was performed on 30 sheep, which were alternatively closed either by a double-layer running suture at 90 degrees to the cartilaginous rings or with an automatic stapling device. Exactly 14 days after pneumonectomy, the animals were sacrificed and the trachea with the bronchial stump was retrieved. Sutures were placed under pressure until air leakage was observed. The air-leakage pressure was recorded digitally. RESULTS: In both groups, there was no evidence of a bronchopleural fistula. As in the previous experimental study, mean values of air-leakage pressure revealed a large standard deviation in both groups (min. 0.16-max. 1.15 bar). Unlike the results in the first experiment there was no statistically significant difference between the two groups. CONCLUSIONS: After 14 days, when a bronchial stump is considered to be healed, the resistance to pressure of a mechanical suture is equal to that of the manual suture.

A comparison of bronchial closure with the aid of staples or suture: an experimental study on pig tracheae.

The objective of this study was to determine the resistance to pressure of a bronchial stump depending upon the closure technique. For the experimental study, 30 pig tracheae were alternatively closed either by a double-layer running suture at 90 degrees to the cartilaginous rings or with an automatic stapling device. Sutures were placed under pressure until air leakage was observed. The air leakage pressure was digitally recorded. A statistically significant difference existed between the two groups. The mechanical suture proved more resistant to pressure (p =.011). Thus, under ideal conditions, the resistance to pressure of a mechanical suture is equal to, if not better than, that of the manual suture.

A comparison of interrupted and continuous sutures for tracheal anastomoses in sheep.

OBJECTIVE: To study the tensile strength of tracheal anastomoses. DESIGN: Experimental study. SETTING: University medical school laboratory, Germany. ANIMALS: 15 sheep. INTERVENTIONS: Tracheal anastomoses with three different suturing techniques: a continuous suture and interrupted sutures with either a monofilament or a polyfilament material. Anastomoses were tested to breaking after being in place for 1, 2, 4, 8 or 24 weeks. RESULTS: After one week, with all three materials, the trachea broke at the anastomosis. In animals that survived longer, the trachea broke further away from the anastomosis. There was no significant difference between the mean values of the breaking force for continuous sutures and single interrupted sutures (p = 0.9). CONCLUSION: The suturing technique (continuous or interrupted) has less relevance for the tensile strength of the anastomosis than in vitro experiments suggest.

The mechanical stability under load of tracheal anastomoses after various phases in vivo.

OBJECTIVE: The objective of our study was to postoperatively examine the mechanical stability under load of tracheal anastomoses over different periods in time and to compare these with native tracheae. STUDY DESIGN: A randomized experimental study on animals. METHOD: We performed tracheal anastomoses on sheep with three different suturing techniques and different resection lengths (3, 6, and 9 cm): These anastomoses were subjected to a breaking test at different intervals in vivo (1, 2, 4, 8, and 24 wk) and compared with the tracheae of healthy sheep. RESULTS: After 1 week in vivo, the anastomosis itself tore off from the remaining trachea under tension, regardless of the suturing technique used and the length of resection. With all animals that survived for a longer period, the trachea broke a greater distance away from the anastomosis. The necessary breaking forces were only minimally lower than those required for breaking healthy tracheae and the difference is statistically insignificant. When all operated tracheae are combined and the forces compared with native tracheae, this reveals that the operated tracheae are significantly more stable (P =.015) and present a lower longitudinal elasticity (P =.004). CONCLUSION: During the first postoperative days, the stability under load of tracheal anastomoses is slightly lower than that of healthy trachea. This difference is, however, far from those values that can be measured intraoperatively on tracheal anastomoses. Thus, supplementary measures for the mechanical protection against suture line separation do not seem necessary.