Polytetrafluoroethylene microprosthesis in the arterial system of the rat

The experimental behavior of a 1-mm internal diameter (i.d.) polytetrafluoroethylene (PTFE) microprosthesis, as a substitute for an abdominal aortic segment in the rat, was reviewed. Fifty Wistar rats were divided into four groups: Group I--12 rats with autotransplant of an abdominal aortic segment (AAS); Group II--12 rats with allotransplant of an AAS obtained from Long-Evans rats; Group III--12 rats with xenotransplant of an AAS taken from rabbit femoral arteries; and Group IV--14 rats with substitution of an AAS by a 1-mm i.d. PTFE microprosthesis. The rats were sacrificed at different time intervals ranging from five to 360 days, with previous aortography. In Group I, there was a 100 percent patency at a mean of 152.41 days; in Group II, a 91.6 percent patency at a mean of 100.08 days; in Group III, an 83.3 percent patency with a 75 percent aneurysmal dilation at a mean of 107.58 days; in Group IV, a 71.42 percent patency with two anastomotic aneurysms at a mean of 105 days (P less than 0.05, chi square) between Groups I and IV, autotransplant vs. PTFE). The 1-mm PTFE microprosthesis placed in the arterial system of the rat proved to be a reliable alternative for microvascular substitution.     

Venous prostheses: improved patency with external stents

A uniformly successful prosthesis for replacement in the venous system has not been developed. This study assesses the effect of external stents on the patency of polytetrafluoroethylene (PTFE) grafts in the infrarenal vena cava. Under general anesthesia, 21 mongrel dogs underwent midline laparotomy. The infrarenal vena cava was resected and replaced by a standard segment (8 cm X 10 mm) of stented PTFE (12 dogs) and nonstented PTFE (9 dogs). Patency was assessed by contrast venography and the results compared between the two groups. The 7-, 30-, and 90-day patency was 12/12, 10/12, and 9/12, respectively, for stented PTFE and 6/9, 2/9, and 2/9, respectively, for nonstented PTFE. The patency of externally stented PTFE at 30 and 90 days was significantly better than grafts fashioned from PTFE alone (P less than 0.05 by chi-square analysis). These data demonstrate that external stenting improves the early patency of PTFE prostheses in the infrarenal vena cava. Consideration should be given to the clinical use of externally stented PTFE when prosthetic replacement in the venous system is required.     

Long-term results of treatment of Budd-Chiari syndrome with portal decompression.

Thirty-three patients with Budd-Chiari syndrome were studied for 1 to 19 years following portal decompression. All had ascites, hepatomegaly, abnormal liver function, angiographic demonstration of inferior vena cava and/or hepatic vein occlusion, and biopsy specimens showing intense hepatic congestion and necrosis. When thrombosis was confined to hepatic veins (20 patients), side-to-side portacaval shunt resulted in 95% operative survival, 90% prolonged survival, permanent shunt patency, relief of ascites, reversal of liver dysfunction, and reversal or improvement of hepatic lesions. When thrombosis involved the inferior vena cava, mesoatrial shunt (eight patients) was unsatisfactory because of a 63% mortality rate from liver failure due to shunt thrombosis. In contrast, a new procedure consisting of combined portacaval and caval-atrial shunts (five patients) has been highly successful, with 100% survival, shunt patency, relief of ascites, and reversal of pathologic abnormalities.     

应用PTFE人造血管行门腔H型吻合治疗门静脉高压症

目的　了解血管移植物PTFE在H型门腔分流道的通畅率,分流口径对向肝血流的影响以及减压效果和并发症。方法　用内径10mm普通型PTFE和带支撑环的PTFE分别为12例及8例肝硬化门静脉高压症患者进行了门腔静脉间的H型分流术。其中肝功能ChildA级13例,B级5例,C级2例。平均年龄434岁。结果　无手术死亡。术后平均随访172个月,脑病Ⅰ～Ⅱ级2例,无曲张静脉破裂再出血。术后门脉系统彩色多普勒超声及血管造影检查,向肝血流量无明显影响,分流道通畅率90%。普通PTFE者血栓形成2例(167%);带支撑环PTFE者无血栓形成。结论　该技术在减低门静脉压力,维持向肝血流,预防再出血等方面均取得了良好结果,其中带支撑环者优于普通型。     

Prosthetic replacement for the thoracic vena cava: an experimental study

The superior vena cava (SVC) and thoracic inferior vena cava (IVC) were replaced in 46 dogs with autologous vein, knitted Dacron, glutaraldehyde-fixed porcine pericardium, unsupported polytetrafluorethylene (PTFE), and externally stented PTFE. After 30 days, patency rates were determined by contrast venography and were 100%, 9%, 50%, 75%, and 100%, respectively. The patency rates of Dacron and glutaraldehyde-fixed pericardium are considered unacceptable when compared to autologous vein (p less than 0.05). Stented PTFE exhibited a patency rate equal to that of autologous vein at 30 days, minimal graft reaction, excellent incorporation by host fibroblasts, and a smooth neointima. The external spiral support added to PTFE enchanced the thromboresistance of this graft in the thoracic venous system. Long-term follow-up is required to determine if the stented PTFE prosthesis remains comparable to autologous vein as a venous conduit.     

Doppler echography in the intraoperative assessment of the liver circulation: an experimental study in swine

In this experimental study the authors report an experience in the evaluation of hepatic blood flow with intraoperative echo-Doppler during orthotopic liver transplantation and side-to-side or end-to-side portacaval shunt. Doppler ultrasonography studied the flow of portal vein, hepatic artery and inferior vena cava before the recipient hepatectomy, and after reperfusion during liver grafting. Furthermore echo-Doppler of the portal system was performed to confirm portacaval shunt efficacy. Usually intraoperative Doppler ultrasonography may give informations about the patency of the shunt and regarding the development of early hepatic artery thrombosis during liver transplantation, but often unclear is the exact evaluation of the velocity of the blood flow through the liver. Further experimental studies and clinical evaluations need to find safe parameters and markers of vascular alteration using this superior diagnostic procedure.     

Immediate and long-term results of superior mesenteric vein-inferior vena cava shunt for portal hypertension in children.

Experience with 46 superior mesenteric vein-inferior vena cava shunts in children is reported, with postoperative follow-up of from 2 to 15 yr. The first procedure used as an end-to-side implantation of the vena cava into the right side of the superior mesenteric vein or portal vein after ligating the cava above the iliac vessels (16 cases). In the next 30 children, the vena cava was lengthened using the left or right common iliac vein, thus obtaining better anastomosis and reversed portal flow. Patency may be definitely assumed when the esophageal varices have disappeared within 3 mo; this was observed in 33 children. Results are nearly the same with superior mesenteric vein-inferior vena cava shunt, splenorenal shunt and portacaval shunt when the respective veins of the portal system are more than 1 cm in diameter. When it is less, the superior mesenteric vein-inferior vena cava shunt is more successful than others; this is the case in children under 7 yr of age. No serious trouble was observed after the interruption of the venous circulation of the limbs and pelvis when a superior mesenteric vein-inferior vena cava shunt was performed when the patients were less than 15 yr of age.     

Regular ultrasonographic screening significantly prolongs patency of PTFE grafts

BACKGROUND: Polytetrafluoroethylene (PTFE) dialysis grafts have considerably shorter patency than native arteriovenous fistulas, despite the use of a complex of screening monitoring methods (venous pressure, access flow). PTFE grafts are used often in subjects with depleted subcutaneous veins after previous abandoned accesses, so keeping the access patent is crucial. We hypothesized that regular duplex Doppler ultrasound screening for access stenoses, together with their sooner treatment, would prolong PTFE graft patency. METHODS: We performed a randomized, prospective study of PTFE grafts' cumulative patency in 192 subjects. In group 1, regular ultrasound examinations performed every 3 months was added to traditional screening (i.e., regular access examination at hemodialysis unit, monitoring of venous pressure and access flow). Group 2 was screened only traditionally (without ultrasound). Interventions of suspected stenoses were indicated by nephrologists, vascular surgeon, and, in group 1, also by ultrasonography. Classic ultrasound criteria for significant stenosis were used, even if the access flow had not been decreased. The mean follow-up lasted 392 +/- 430 days. RESULTS: Groups were similar with respect to age, gender, diabetes status, and number of previous abandoned accesses. Group 1 had significantly longer access patency (P < 0.001). Number of interventions per graft was 2.1 +/- 1.8 and 1.3 +/- 1.0 in group 1 and group 2. CONCLUSIONS: Regular screening duplex Doppler ultrasonography results in significantly longer PTFE graft patency due to early detection of access stenosis and, thus, more frequent elective interventions of access stenoses.     

Patency of polytetrafluoroethylene microarterial prostheses improved by ibuprofen

Because of the increasing need for a reliable prosthetic microvascular graft, we investigated the patency of expanded PTFE with and without platelet inhibitor medication as an arterial prosthesis (1 by 10 mm) placed in the aorta of the rat using standard microsurgical technique. In 10 animals without platelet-inhibitor medication, one graft (10 percent) was patent at 30 days. When the platelet inhibitor ibuprofen was given for the initial 15 days to 10 animals, all 10 grafts (100 percent) remained patent at 30 days without further use of the drug. There was a significant difference between the patency achieved with the drug and that obtained without it (p < 0.0001). The results of this experimental study demonstrate that expanded PTFE can successfully be used as a microvascular graft in the rat with excellent patency (100 percent at 30 days) when combined with ibuprofen therapy.     

The use of long synthetic microvascular grafts to vascularise free flaps in rabbits

A 5 cm length of 2 mm internal diameter (i.d.) synthetic, expanded polytetrafluoroethylene (PTFE, or Gore-Tex) vascular graft was used to connect 25 rabbit inferior epigastric flaps to the contralateral femoral vessels. In 15 animals an expanded PTFE graft connected the opposite femoral artery to the flap while the ipsilateral venous drainage remained intact. In the remaining 10 animals an expanded PTFE graft was used to replace the venous drainage of the flap and connected to the opposite femoral vein while the ipsilateral femoral artery supplied the flap. Flap survival and graft patency were evaluated over 3 weeks. Ten of 15 flaps with intra-arterial grafts survived at 3 weeks (67%). Only 27% (4/15) of their supplying grafts remained patent for 3 weeks, although 67% (10/15) were patent at 10 days. All 10 flaps, where expanded PTFE grafts replaced venous outflow, failed within 36 hours. At exploration these grafts were thrombosed or collapsed. In conclusion, currently available 2 mm (i.d.) expanded PTFE vascular graft cannot maintain patency in a low blood flow circulation supplying an isolated free flap.     

直接性肝内门腔分流的临床应用

目的探讨在肝后段下腔静脉(RHSIVC)与肝内门静脉之间建立直接性肝内门腔分流(DIPS)的临床应用价值。方法采用B超结合X线透视引导穿刺,为13例门脉高压患者(3例同时合并有肝癌)实施DIPS术,对1例合并有肝癌的患者同时行经肝动脉化疗栓塞术(TACE)。所有患者术前均行上腹部增强CT检查,测量RHSIVC的直径、长度及周围肝实质包绕RHSIVC的范围,分别对患者术前、术后红细胞计数、血红蛋白量、肝功能、血氨水平及门腔压力差的改变进行比较,采用彩超对分流道的通畅情况进行随访。结果13例DIPS术均获成功,患者门腔压力差由术前的(27.94±5.29)mmHg(16～35mmHg)降至分流后的(9.22±1.83)mmHg(12～30mmHg)(P<0.001)。术后3天,1例肝癌患者(同时行TACE术)死于急性肝功能衰竭;另1例患者出现血性腹腔积液;其余11例患者无严重的并发症发生。12例存活患者分流道平均通畅时间为176天,术后30、90、180天分流道的累计通畅率分别为100%、80%、80%。结论在RHSIVC及门静脉之间建立DIPS安全、可行,可作为传统TIPS术的改良与补充,在临床上进一步推广。     

Meso-atrial shunt in the surgical treatment of Budd-Chiari syndrome

Three patients with idiopathic Budd-Chiari syndrome with occlusion of the hepatic veins and significant obstruction of the hepatic segment of the inferior vena cava are presented. The inferior vena caval obstruction precluded the use of conventional side-to-side portacaval or mesocaval shunts. Dramatic regression in liver size and resolution of ascites occurred in all three patients following the construction of meso-atrial shunts using wide-lumen woven Dacron grafts. Shunt patency was confirmed by angiography in two patients and Doppler studies in one. One patient died five months after surgery and another after 16 months. The shunts were widely patent at autopsy and the full length of the grafts were lined by neo-intima. The third patient is asymptomatic 20 months after surgery and is free of ascites. Our experience in these three cases suggests that patency can be expected in long synthetic grafts between the portal and systemic venous system provided the shunt is of adequate diameter and there is a pressure gradient between the two ends.     

Transjugular intrahepatic portosystemic shunt vs. small-diameter prosthetic H-graft portacaval shunt: Extended follow-up of an expanded randomized prospective trial

We report herein the results of extended follow-up of an expanded randomized clinical trial comparing transjugular intrahepatic portosystemic shunt (TIPS) to 8 mm prosthetic H-graft portacaval shunt as definitive treatment for variceal bleeding due to portal hypertension. Beginning in 1993, through this trial, both shunts were undertaken as definitive therapy, never as a “bridge to transplantation.” All patients had bleeding esophageal/gastric varices and failed or could not undergo sclerotherapy/banding. Patients were excluded from randomization if the portal vein was occluded or if survival was hopeless. Failure of shunting was defined as inability to shunt, irreversible shunt occlusion, major variceal rehemorrhage, hepatic transplantation, or death. Median follow-up after each shunt was 4 years; minimum follow-up was 1 year. Patients undergoing placement of either shunt were very similar in terms of age, sex, cause of cirrhosis, Child’s class, and circumstances of shunting. Both shunts provided partial portal decompression, although the portal vein-inferior vena cava pressure gradient was lower after H-graft portacaval shunt (P<0.01). TIPS could not be placed in two patients. Shunt stenosis/occlusion was more frequent after TIPS. After TIPS, 42 patients failed (64%), whereas after H-graft portacaval shunt 23 failed (35%) (P <0.01). Major variceal rehemorrhage, hepatic transplantation, and late death were significantly more frequent after TIPS (P <0.01). Both TIPS and H-graft portacaval shunt achieve partial portal decompression. TIPS requires more interventions and leads to more major rehemorrhage, irreversible occlusion, transplantation, and death. Despite vigilance in monitoring shunt patency, TIPS provides less optimal outcomes than H-graft portacaval shunt for patients with portal hypertension and variceal bleeding. Presented at the Forty-First Annual Meeting of The Society for Surgery of the Alimentary Tract, San Diego, Calif., May 21–24, 2000.     

Aspirin improves the patency rate of seeded vena cava grafts

The purpose of this study was to evaluate the effectiveness of aspirin (ASA) and porcine endothelial cell seeding in improving the patency rate of vena cava grafts. Thirty-nine dogs underwent infrarenal vena cava replacement by 10 cm lengths of 8 mm I.D. ringed polytetrafluoroethylene grafts. Thirty-one grafts were seeded with 1-1.5 x 10(6) porcine aortic endothelial cells while eight were not (GIII). Of the seeded group, 16 animals received no ASA (GI), while 15 others (GII) were given ASA (325 mg) daily starting two days preoperatively and continuing until sacrifice. Venograms were performed on the fourth postoperative day. Grafts were harvested 32 days after insertion and evaluated for patency rate and endothelialized surfaces. The 32-day patency rate was significantly higher for GII than for GI and III animals (67% vs. 13 and 25% respectively). Endothelialized surface was higher in GII than Gi and III (67% vs. 16% and 18% respectively). We conclude that endothelial cell seeding alone does not prevent graft closure and that a combination of ASA and cell seeding significantly increases the patency rate of vena cava grafts.     

一种新型大鼠门腔静脉转位模型的建立

目的探讨一种新型大鼠门腔静脉转位模型建立的可行性。方法大鼠40只,采用袖套法建立同种异体血管门腔静脉转位模型。于左肾静脉末端安装一袖套,将左肾静脉与门静脉残端借袖套连接,贴近左肾静脉上方结扎并剪断下腔静脉,将下腔静脉借同种异体血管及袖套与肠系膜上静脉连接。另取10只大鼠切除左肾后作为对照组。观察术后大鼠的体重、生化指标、核磁共振及其肝脏病理学变化。结果40只大鼠门腔静脉转位后近、远期存活良好,术后24h至2月存活率均为97．50％（39／40）。术后2周核磁共振检查显示血流通畅。与对照组比较,实验组大鼠术后2月白蛋白、谷丙转氨酶、碱性磷酸酶和总胆红素、体重等指标差异均无统计学意义。术后2月肝组织病理检查结果正常。结论采用同种异体血管借助袖套方法建立大鼠门腔静脉转位模型是可行的。     

Experimental microvenous reconstructions with Gore-Tex polytetrafluoroethylene prosthesis implanted by means of the sleeve anastomotic technique

Polytetrafluoroethylene (PTFE) prostheses (Gore-Tex; ID, 1 mm; length, 5-7 mm; wall thickness, 0.2 mm; fibril length, 30 microns, n = 28) were implanted into the rat femoral vein by means of the sleeve anastomotic technique to enhance the patency rate. In the control group, PTFE prostheses (n = 8) were implanted by means of the end-to-end technique. In the experimental group patency and healing of the PTFE prostheses were evaluated at 1 day (n = 4), 1 week (n = 6), 3 weeks (n = 6), 6 weeks (n = 6), and 12 weeks (n = 6) after implantation by means of macroscopic inspection and routine light and scanning electron microscopy. All prostheses, except one at 1 week after implantation, were patent at the time of removal. All of the microvenous prostheses were completely covered by an endothelial layer at 3, 6, and 12 weeks after implantation. Occasionally some smooth muscle-like cells could be found underneath this endothelial layer, but stenosis was never observed at the anastomotic sites. Only scarce tissue ingrowth was observed in the wall of the PTFE prostheses. In the control group, all prostheses, except one prosthesis after 3 weeks, were found to be occluded. An occlusive mural thrombus was found firmly attached at the anastomoses at 1 day, and an organized thrombus at 3 weeks after implantation. The patent prosthesis demonstrated complete endothelial healing. These results demonstrate the importance of the sleeve anastomotic technique and the potential of PTFE prostheses as a microvenous conduit when implanted by means of the sleeve anastomotic technique in experimental reconstructive microvascular procedures.     

Identification of an experimental model of partial portocaval shunt

Portacaval shunt with interposition of 6 mm H-graft of PTFE is a real partial shunt. In this experimental study, the operation has been well tolerated and has been compared with 8 mm H-graft and direct "vein to vein" portacaval shunt. Intraoperative data show that 6 mm is the ideal diameter for a portacaval shunt to prompt an experimental model based on partial decompression of portal bed in animals in this size.     

Effects of hypertonic saline-dextran solution on regional blood flow and thrombogenicity in PTFE grafts in the vena cava of the rabbit.

OBJECTIVES: to study the effects of hypervolaemic haemodilution with hypertonic saline-dextran solution (HSD) on regional blood flow and thrombogenicity of small diameter polytetrafluoroethylene (PTFE) grafts. DESIGN: blood flow in rabbit aorta, vena cava and femoral, renal and ear arteries was determined in five groups: controls, isovolaemic haemodilution with dextran-70 (10 ml/kg body weight (b.w. )), hypervolaemic haemodilution (10 ml/kg b.w.) with either dextran-70, 7.5% NaCl or a combination of dextran and NaCl (HSD). In a second series PTFE grafts were inserted into the vena cava of rabbits treated with hypervolaemic haemodilution with dextran, hypertonic saline or HSD and examined after two days. RESULTS: blood flow increased in aorta, vena cava and femoral artery after haemodilution. The increase was transient in animals treated with hypertonic NaCl alone but sustained in the dextran-70 groups. The grafts from animals treated with hypertonic saline alone had a lower thrombus mass and higher blood flow compared to those from rabbits haemodiluted with dextran-70 only, indicating that both dextran and NaCl have antithrombotic effects. Superior results were obtained with HSD solution. CONCLUSIONS: HSD solution has a strong flow-promoting action in several vascular beds and beneficial effects on the patency of small diameter vessel grafts.     

Superior vena cava occlusion. Demonstration of surgical therapeutic possibilities

Surgical problems in treatment of superior vena cava syndrome are discussed by our population of 15 patients and the literature. Nine patients which suffered from caval thrombosis were managed by thrombectomy. In four cases superior vena cava was bypassed or replaced by PTFE (Gore-Tex) tubular grafts successfully. Whereas autologous vein as spiral composite graft or complete venous conduit might be preferred by reason of excellent longtime patency rates, the every time available PTFE vascular prosthesis appears to be an efficient synthetic material for replacement of superior vena cava.     

New microvenous anastomosis model for microsurgical training: external jugular vein

In microsurgical training, the femoral vein is used frequently for a microvenous anastomosis model. But the femoral vein in the rat does not completely simulate the human vein because of its thin wall, fragility, and tendency to collapse. These anatomic characteristics cause some difficulty in carrying out anastomoses in microsurgery training particularly for beginners. The authors propose the external jugular vein of the rat for microsurgical training in microvenous anastomoses. In 10 Wistar rats, the anatomy of the external jugular vein was studied by dissection and histology. Anatomic dissections demonstrate that the external jugular vein has an average diameter of 1.9 mm (range: 1.6 to 2.1 mm) without tendency to collapse. The vein is easily dissected without any accompanying anatomic structure for an average segment of 45 mm, allowing effortless approximator clamp placement. Comparison of its cross section with that of the femoral vein and other previously described models by light microscopy and scanning electron microscopy reveals a larger diameter and much thicker vessel wall with a prominent tunica media and adventitia. Based on the anatomic findings in 20 rats, the external jugular vein was anastomosed with end-to-end standard microsurgical technique using 8-0 (n = 10) and 10-0 (n = 10) nylon sutures. Results indicate a 100 percent patency rate immediately after the anastomosis for the two subgroups and 100 percent and 90 percent patency rates 1 week after the procedure for the 10-0 and 8-0 nylon suture groups, respectively. This model presents some advantages: the vein is easily dissected with the naked eye without using the operating microscope because it is the largest vein among the superficially located veins in the rat, and has a thick vessel wall without tendency to collapse. The operative area allows for training inbilateral microsurgical anastomoses using a single skin incision and is safe from autocannibalization. The model simulates clinical microvenous anastomosis better because of its similarities to human large diameter flap veins.