Autonomization of epigastric flaps in rats

The question of how long a flap depends on its pedicle cannot be answered clearly from the available literature. To address this, we investigated the time to flap autonomization in the wound bed and the length of time to the point when flap necrosis is reduced to a clinically negligible level. The superficial epigastric flap was raised in 24 rats. After 3, 5, 7, or 10 days of wound healing, the pedicle was again exposed, ligated, and divided. Values of blood flow (flow), velocity (velocity), hemoglobin level (Hb), and oxygen saturation (SO ₂) were noninvasively measured using Laser spectrophotometry. The area of necrosis of the flap was 62.77 ± 1.71% after 3 days, 16.26 ± 0.86% after 5 days, 2.88 ± 0.14% after 7 days, and 1.64 ± 0.16% after 10 days (P < 0.001). Hb, flow, and velocity were found to be significant factors on developing flap necrosis at the preoperative and postoperative time point (P < 0.0001), whereas SO ₂ and flow were significant predictors of necrosis at the time of pedicle ligation (P < 0.0001). The percentage changes of SO ₂ (P < 0.0001), flow (P < 0.0001), and velocity (P = 0.001) between the different time points were significant predictors of flap necrosis. The time needed for the complete autonomization of vascularized free flaps in their wound beds has been found as completed between the 5th and 7th day postoperatively in this rat model. The area of flap necrosis depends on the present value of SO ₂, Hb, flow, and velocity at different time points, but, more importantly, also on the perioperative change of these parameters.