Improving longevity of prosthetic dialysis grafts in patients with disadvantaged venous outflow

OBJECTIVE

Angioaccess for hemodialysis in an extremity with disadvantaged venous outflow has reduced long-term patency. We hypothesized that arteriovenous bridge graft patency could be improved in patients with disadvantaged venous outflow by preoperative venous duplex mapping.

METHODS

The charts of 114 patients who underwent 115 prosthetic arteriovenous bridge grafts were reviewed. Disadvantaged venous outflow was defined on the basis of any combination of prior arteriovenous bridge graft, multiple venipunctures, and clinical examination. Patients were grouped according to the presence or absence of disadvantaged venous outflow. Three groups were analyzed: those with normal venous outflow who had an initial arteriovenous bridge graft (NML), those with disadvantaged venous outflow who had only a clinical examination before redo arteriovenous bridge graft (REDO/DVO), and those with disadvantaged venous outflow who underwent preoperative duplex scanning venous evaluation (MAP/DVO). Life table primary and secondary 12-month patency rates were compared by means of log-rank analysis.

RESULTS

Life table analysis yielded 6-month primary patency rates of 65.9% +/- 5.7%, 66.4% +/- 7.3%, and 43.8% +/- 10.9% for NML, MAP/DVO, and REDO/DVO, respectively. The secondary patency rates at 6 months for NML (91.9% +/- 3.4%) and MAP/DVO (91.1% +/- 4. 9%) were statistically equivalent, and both were significantly better than the patency for REDO/DVO (75.0% +/- 10.0%; P =.004 and P =.04, respectively). This trend persisted beyond 12 months.

CONCLUSION

Preoperative evaluation of venous anatomy in patients with disadvantaged venous outflow results in an arteriovenous bridge graft patency comparable to that seen in patients undergoing initial arteriovenous bridge grafts. Vein mapping improves arteriovenous bridge graft durability in the patient with disadvantaged venous outflow by allowing the surgeon to select venous return that is in direct continuity with the central venous system.

Characteristics of rectal carcinomas that predict the presence of lymph node metastases: implications for patient selection for local therapy

BACKGROUND AND OBJECTIVES

It has been estimated that approximately 5% of middle and low rectal adenocarcinomas are amenable to local therapy. However, these treatment modalities are limited by their failure to identify and treat regional nodal metastases.

METHODS

This study was undertaken to evaluate the role of tumor size, depth of penetration into the rectal wall, degree of histologic differentiation, DNA ploidy status, and their combination on the presence or absence of metastases in perirectal lymph nodes. Logistic regression was used to quantitatively predict the probability of positive lymph nodes.

RESULTS

Tumor size did not correlate with the presence of nodal involvement; however, worsening degree of differentiation, increasing depth of wall penetration and aneuploidy did statistically correlate with the presence of nodal metastases. For any combination of tumor traits, aneuploidy markedly increased the probability of positive lymph nodes over that observed with diploid tumors.

CONCLUSIONS

The combination of degree of differentiation, depth of penetration, and ploidy status may be used to identify patients whose tumors may be adequately treated with local measures. For any combination of tumor traits, aneuploidy markedly increased the probability of positive lymph nodes over that observed with diploid tumors.

Intimal hyperplasia following thrombectomy versus thrombolysis in occluded vein grafts

Although the histologic effects of balloon catheter thromboembolectomy in arteries are well described, little is known about its effects on arterialized vein grafts. A chronic canine model was used to compare the intimal hyperplasia that develops following balloon catheter thrombectomy versus thrombolytic therapy when each treatment was used to open experimentally occluded reversed autogenous vein grafts. Eleven of 12 dogs survived to the time of graft thrombosis and treatment. Ten grafts in one group of animals were treated with shear force-controlled balloon catheter thrombectomy, and eleven grafts in another group of animals were treated with infusion of urokinase (average 355, 833 IU/graft). Explantation and histologic evaluation was performed 5 weeks after treatment. Data were evaluated at comparable anatomic locations. These studies demonstrated the development of intimal hyperplasia in both groups with no statistically significant differences in the intimal thickening between the two treatment groups. It is hypothesized that vessel wall damage occurs at the time of thrombosis with the adherence of thrombus to the wall, and that this may be as important in producing intimal hyperplasia as the effects of carefully performed balloon thrombectomy or lytic therapy.

FGF-1 affixation stimulates ePTFE endothelialization without intimal hyperplasia

The affixation of FGF-1 to porous vascular grafts has been reported to stimulate capillary ingrowth and surface endothelialization. The current study further characterizes responses to fibroblast growth factor (FGF)-1 affixation to 30-cm-long grafts followed 140 days. ePTFE grafts (30 cm x 8 mm i.d.), 60 microns internodal distance, were impregnated with fibrin glue (FG) suspensions containing FGF-1 and heparin. Two negative control groups were treated either with FG with heparin alone or left untreated. Grafts were explanted from the canine thoracoabdominal aortic position after 10, 30, or 140 days (n = 3/time/group) 10 hr after im injection of tritiated thymidine (0.5 muCi/kg). Specimens were studied by light and electron microscopy, immunohistochemistry, morphometric analyses, and cross-sectional autoradiography. RNA preparations from inner capsule tissues were used for reverse transcription-polymerase chain reaction (RT-PCR) analyses of FGF-1, FGF-2, transforming growth factor-beta 1, (TGF-beta 1) and FGF receptor mRNA species. Inner capsule collagen was quantitated by hydroxyproline colorimetry. Histologic analyses of perianastomotic regions were performed for comparison purposes. All explants were patent and without intimal hyperplasia. Progressive capillarization of the internodal spaces occurred over time and was significantly more extensive in the FGF-1-treated group. Endothelialization of the luminal surface increased with time, at 140 days covering 86.7 +/- 11.6% of the FGF-1 explants vs 46.1 +/- 7.5% and 48.1 +/- 13.3% in the other groups, P < 0.007 and P < 0.04, respectively. Inner capsule thickness at 140 days differed significantly (P < 0.05) between the FGF-1 group (138.8 microns) vs either control group (93 and 67 microns, respectively), which did not significantly differ from each other. Cross-sectional autoradiography demonstrated an FGF-1-induced mitotic index increase at 30 days, 9.6 +/- 4.4% compared to 2.5 +/- 1.0 and 0 +/- 0%, respectively, with both myofibroblasts and endothelial cells incorporating the [3H]thymidine label. The mitotic index returned to quiescent levels at 140 days (< 1% in all groups). Collagen content increased with time in all groups, significantly greater in both FG groups vs untreated controls at 30 and 140 days. RT-PCR analyses revealed FGF-1, FGF-2, FGFR-1 (flg), and TGF-beta 1 mRNA in all samples without evidence of modulation by FGF-1 affixation. These data demonstrate FGF-1-induced graft capillarization and surface endothelialization without functionally significant intimal hyperplasia in this model.

Biomaterial-induced macrophage activation and monokine release

This study quantifies macrophage acid phosphatase release as a marker of cell activation when cultured with or without biomaterials. Peritoneal macrophages were harvested from six New Zealand White rabbits and cultured in minimum essential media with 10% equine serum. After cell identification by morphology, nonspecific esterase, and RAM 11 immunoperoxidase, cells were passaged twice, and second-passage macrophages were seeded in 96-well plates (5,000 cells/well) and grown to confluence. After collection of day zero media, circular disks of polyglactin 910 and two types of commercially available polyethylene terephthalate with different construction and sterilization characteristics were placed on the cell monolayer. Controls without biomaterials were also established. Media was collected and pooled for each group and time point beginning on day 2 and continuing every other day for 22 days. Conditioned media were quantitatively assayed for acid phosphatase colorimetrically at 402 nm using p-nitrophenylphosphate as the substrate. Acid phosphatase activity increased progressively at late time points for each group but no difference was noted between groups at any time point. These data show that the activation of cultured macrophages with time is not altered differentially by the presence of biomaterials. The previously demonstrated monokine release following biomaterial exposure is therefore a specific event and not simply part of the generalized activation phenomenon.

Modulation of myofibroblast proliferation by vascular prosthesis biomechanics

Cyclic deformation in vitro modulates smooth muscle cell proliferation. Different degrees of cell deformation occur in vivo on grafts of different compliance. This study evaluates the influence of prosthetic biomechanics on cell proliferation. Two types of composite 80% bioresorbable PG910/20% polypropylene (PP) aortic grafts differing only in the elasticity of the PP were implanted into rabbits. After PG910 resorption, prosthetic biomechanics were determined by PP (% elongation: Group 1, 101 +/- 6 versus Group 2, 63 +/- 4). Killing was performed at 1, 2, 3, and 6 months, and patency, dynamic compliance, mitotic index (MI), and inner capsule thickness (ICT) were determined. Initially all parameters were identical. After PG910 resorption (1-2 months), significant differences were seen. At late analysis, Group 1 MI was significantly greater than Group 2 (3 months: 4.67 +/- 2.5 versus 3.11 +/- 2.5 [p < 0.02]; 6 months: 4.11 +/- 2.3 versus 2.67 +/- 0.9 [p < 0.005]). Inner capsule thickness in Group 1 was also significantly greater than Group 2 (3 months: 219 +/- 20 versus 129 +/- 40 [p < 0.05]; 6 months: 220 +/- 50 versus 130 +/- 40 [p < 0.05]). Dynamic compliance differed at 2 months (p = 0.057). Patency was worse in Group 1 (p = NS). In vivo cellular proliferative activity is directly related to mural cyclic deformation induced by altered biomechanical graft characteristics.

Hepatic insulin resistance during chronic hyperdynamic sepsis

Disturbances in normal glucose metabolism and homeostasis which manifest as hyperglycemia and glucose intolerance are often observed during clinical sepsis. Skeletal and myocardial muscle as well as whole body insulin resistance have been demonstrated in this laboratory and others during experimental and clinical sepsis. The existence of hepatic insulin resistance in sepsis has yet to be fully elucidated. This study was undertaken to assess hepatic insulin resistance during chronic hyperdynamic sepsis. Animals were randomly assigned to a septic (n = 7), sham (n = 7), or control (n = 7) group. Sepsis was induced in anesthetized dogs via a midline laparotomy whereby a fecal-soaked gauze sponge was placed amid the intestines. Sham animals underwent a laparotomy with mechanical manipulation of the intestines but no fecal implant. Control animals had no previous surgery. Sham and control dogs were pair-fed with the septic dogs. On postoperative day 7, after an overnight fast, animals were anesthetized, intubated, and ventilated. Via a left subcostal laparotomy, electromagnetic flow probes were placed to measure hepatic arterial and portal venous blood flows. Cannulae were placed in femoral, portal, and hepatic veins and femoral artery and used to calculate hepatic outputs of glucose, lactate, and oxygen during a basal period and hyperinsulinemic-euglycemic clamps which used intravenous insulin infusions which ranged from 0.4 to 4,000 mU/min. Mean arterial blood pressure decreased with increasing insulin concentrations in septic animals while no change was seen in control or sham animals. In control and sham animals, net hepatic glucose output (NHGO) decreased in response to increasing insulin levels. Septic animals showed no such inverse relationship and, moreover, showed no change in glucose output response to any insulin infusion, i.e., hepatic insulin unresponsiveness during sepsis. Net hepatic lactate output during basal pre-insulin period during sepsis was negative. This was in contrast to the positive outputs in control and sham animals. Glucose infusion rates (GIR) increased during insulin infusion but were not different between groups at any insulin infusion rate. These data demonstrated a hepatic insulin resistance (unresponsiveness) during chronic hyperdynamic, hypermetabolic sepsis.