The use of an absorbable collagen cover (NeuraWrap) improves patency of interpositional vein grafts

Objectives: Autologous interpositional vein grafts are used in peripheral arterial bypass procedures. Sudden exposure of vein grafts to arterial blood pressure is associated with increased wall tension leading to overdistension of the graft and changes in flow patterns. Overdistension of vein grafts often results in anastomotic leaks, thrombosis, and loss of patency. This study was designed to evaluate the use of a biodegradable collagen cover as a means of preventing overdistension of venous bypass grafts in a rat model. Methods: Twenty-two Sprague-Dawley female rats weighing 250-350 g were randomly assigned to two groups: study group (n=15) and control group (n=7). In all the rats, a 10-mm segment of the left femoral vein was harvested and used as a graft in repair of a right femoral artery injury. Following this procedure, control rats remained untreated. After completion of the femoral artery repair in the study group, the graft was wrapped with a collagen cover of appropriate length (NeuraWrap Nerve Protector) and sutured to form a tube around the vein graft. At the end of the procedure, the intensity and duration of bleeding, and vessel patency were recorded and the proximal and distal arterial segments were examined by Doppler ultrasonography. All observations and measurements were repeated at 1 and 2 hours after surgery. After the second hour, all the rats were sacrificed and vein graft samples with the arterial portions were removed for histological study. Results: After removal of the vascular clamps of the control group, a sudden distension was observed in all the vein grafts. In this group, bleeding at the anastomosis site lasted for I to 3 minutes and was followed by ballooning of the grafts. In the study group, however, none of the samples exhibited distension and ballooning. There was no bleeding in 11 samples at all, and bleeding time was less than one minute in the remaining four samples. In the control group, only one graft was patent at two hours, one of the grafts was occluded after only three minutes. In the study group, all the grafts were patent and no thrombosis was noted. The mean blood flow velocity of the control group measured at 0 hour by Doppler ultrasonography was 0.93 +/- 0.33 cm/sec in the proximal artery, and 0.73 0.44 cm/sec in the distal artery. The mean blood flow velocities in the proximal and distal arteries of the study group were as follows, respectively: at 0 hour: 0.45 0.27 and 0.46 0.22 cm/ sec; at 1 hour: 0.40 0.22 and 0.62 0.40 cm/sec; and at 2 hours: 0.55 0.22 and 0.64 0.37 cm/sec. Conclusion: Prevention of overdistension of vein grafts with the use of an external cover decreases anastomotic leaks, protects the intimal media, maintains blood flow, reduces the incidence of thrombosis, and thus provides a higher patency rate.