A nitinol "U-Clip" versus sutured arteriovenous anastomosis: local tissue response and intimal hyperplasia development in a sheep model.

OBJECTIVES: This study sought to compare the local tissue response and subsequent volume of intimal hyperplasia (IH) that develops throughout the maturation of an arteriovenous fistula created using continuous/interrupted polypropylene with that of a novel, metal-alloy, penetrating anastomotic clip device. MATERIALS AND METHODS: Forty-six fistulae were created in 23 sheep under a paired design using the nitinol U-Clip (n = 23) in one hind limb and continuous (n = 20) or interrupted (n = 3) polypropylene suture for the other. Animals were killed at 4 (n = 3), 14 (n = 3), 28 (n = 10), 42 (n = 3), and 180 (n = 4) days. Histological sections were evaluated for quantitative histology and immunohistochemistry. RESULTS: Compared with continuous polypropylene, U-Clip specimens demonstrated less intima-media area per unit length (IMA/L), proliferating cells, and tissue necrosis at all time points (MANOVA, F = 9.8-24.1, all p ≤ .005; observed power >82%). Specifically, values of IMA/L were reduced by 5% (p = .97), 37% (p = .02), 33% (p < .01), 9% (p = .42), and 14% (p = .22) at the time points of 4, 14, 28, 42, and 180 days respectively. Proliferating cells were reduced by 75% (p < .01), 72% (p = .03), 76% (p = .03), 27% (p = .31), and 60% (p = .01) and tissue necrosis by 67% (p < .01), 58% (p = .02), 40% (p = .33), 21% (p = .43), 77% (p = .11). In a 28-day comparison between U-Clip and interrupted polypropylene the U-Clip group demonstrated a 4% (p = .65) reduction in IMA/L, 74% (p < .01) in proliferating cells and 49% (p < .05) in tissue necrosis. CONCLUSIONS: These results provide evidence of reduced local tissue necrosis, proliferating cells, and IH, favouring arteriovenous fistulae created using the U-Clip anastomotic device over conventional polypropylene suture techniques most evident over the first 4 weeks.

An arteriovenous fistula model of intimal hyperplasia for evaluation of a nitinol U-Clip anastomosis.

OBJECTIVES: The aim of this study was to create an ovine arteriovenous fistula (AVF) model which would closely replicate a human forearm fistula and use this to quantify the degree of intimal hyperplasia in those created with the U-Clip compared to a conventional sutured anastomosis. MATERIALS AND METHODS: Twenty AVFs were created in 10 Border Leicester-Merino sheep between the superficial femoral artery and vein of each hind limb. On one side the U-Clip and on the other a continuous polypropylene suture was used to perform the anastomosis. The animals were sacrificed at 2 (n = 3), 4 (n = 4), 6 (n = 3) weeks and histological slices were taken of each AVF in cross section to determine the intimal media area per unit length (IMA/L). RESULTS: Intimal hyperplasia (IH) was observed at all time points with one AVF found occluded with thrombus at the time of harvest. The IMA/L was significantly lower in the U-Clip groups by 24% at 2 weeks, 32% at 4 weeks and 23% at 6 weeks (Two-way ANOVA, p = 0.019, observed power = 0.825, time or side p ≥ 0.766, type p = 0.001; Paired t-test, p < 0.001 between matched anastomotic types). Time taken to perform the anastomosis was similar between the two anastomotic techniques (Polypropylene 14(8-18) vs. U-Clip 15.3(11-23) min; p = 0.47). CONCLUSION: This ovine AVF model results in IH similar to that seen in a human AVF. The IH that occurs with the U-Clip is less than that of continuous polypropylene suture.

Gastrointestinal lavage reduces total body water.

BACKGROUND: The aim of this study was to measure changes in total body water (TBW) in surgical patients after gastrointestinal lavage. METHODS: In a prospective, controlled study we used bioelectrical impedance to calculate the change in TBW in two groups of general surgical patients in the pre-operative period: the colonic lavage group consisted of patients fasted overnight who received 3 L of gastrointestinal lavage solution (GLS; n = 30), and the control group consisted of patients fasted overnight only (n = 30). Total body water was measured before and after either lavage and fasting (lavage group) or fasting alone (control group). RESULTS: The lavage group had a mean TBW loss of 729 mL +/- s.e. 217 and the control group a mean loss of 84 mL +/- s.e. 93 (P < 0.01 unpaired t-test). CONCLUSIONS: The results suggest that GLS results in a net loss of TBW. Although this fluid loss is modest, it may be important in surgical patients who have minimal cardiovascular reserve.