The timing and nature of neovascularization of jejunal free flaps: An experimental study in a large animal model

The present study was designed (1) to determine whether a free jejunal tran sfer in a large animal model can develop collateral circulation that is ade quate to maintain viability after division of the pedicle and (2) to determ ine the earliest time pedicle ligation is safe after transplantation. A 15-cm jejunal segment was transferred to the necks of 18 dogs weighing 25 to 35 kg. The bowel segment was inset longitudinally under the skin on one side of the neck, partially covered by the neck muscles, and the mesenteri c vessels were anastomosed to recipient vessels in the neck. The proximal a nd distal bowel stomas were exteriorized through skin openings 12 cm apart and matured. The dogs were subjected to ligation of the vascular pedicle at different intervals: postoperative day 7 (group I, n = 3), day 14 (group I I, n = 5), day 21 (group III, n = 5), and day 28 (group IV, n = 5). Blood p erfusion was measured in the proximal and distal bowel stomas before pedicl e division (control) and 24 hours later using hydrogen gas clearance and fl uorescein dye. Bowel necrosis was analyzed using planimetry. The bowel was also stained with hematoxylin and eosin and factor VIII, and new blood vess els were counted. Mean values (+/- standard deviation) were compared with c ontrol values for each test and with normal values in the intact bowel usin g analysis of variance with Neumann-Keuls post-hoc test for multiple compar isons. No jejunal free flaps survived when the vascular pedicle was divided 1 week postoperatively, Bowel survival was 60 percent at 2 weeks, 83 percent at 3 weeks, and 100 percent at 4 weeks. Hydrogen gas clearance values (ml/min/1 00 g) were 49.6 +/- 8.7 in the mucosa of the intraabdominal jejunum and 37. 9 +/- 9.4 in the jejunum that was transferred to the neck before division o f the pedicle. Twenty-four hours after pedicle division, hydrogen gas clear ance values were 2.8 +/- 6.4 in group I (p < 0.05), 22.4 +/- 12.4 in group II, 23.9 +/- 9.3 in group III, and 34.2 +/- 7.5 in group IV. FluoroScan rea dings in the transferred jejunum were 201 +/- 7.2 in the control group, 9.3 +/- 2.8 in group I (P < 0.05), 79.1 +/- 10.6 in group II, 66.2 +/- 7.3 in group III, and 164 +/- 11.9 in group IV. New vessel formation as identified by factor VIII staining correlated with increasing bowel perfusion and fla p survival rate. Bowel neovascularization, perfusion, and survival increased progressively 1 week after transfer. Significant portions of the transferred bowel will ne ovascularize and survive as early as 2 weeks postoperatively. However, a mi nimum of 4 weeks before ligation of the pedicle is necessary to maximize fl ap perfusion and guarantee survival.