Extended Rat-Ear Flap Model: A New Rodent Model for Studying the Effects of Vessel Supercharging on Flap Viability

ABSTRACT

A new extended rat-ear flap model, with both an axial and a random component, is described. The flap is based on an axial supply by the posterior auricular artery and the posterior facial vein. The random portion, consisting of the rat dorsum, is capable of being supercharged at two separate sites-in the scapular and pelvic regions. There are several advantages to this composite flap. It is a combined axial and random flap. When used as a free flap, the viability of the axial portion serves as an indicator for anastomotic patency. The random portion allows for the investigation of the effects of pharmaceutical manipulation or surgical intervention, e.g., flap supercharging. The results indicate that the axial supply alone can cover approximately 50 percent of the extended rat-ear flap. Moreover, adding supercharging perforators to the random portion significantly increases the area of flap survival. Of interest, an axial vascular supply, coupled with more distal dorsal perforators (pelvic) than proximal (scapular) perforators, may increase survival for the so-called ``watershed'' area in the middle of the random portion of the flap.

Additionally, this study also investigated the relative importance of arterial supply vs. venous drainage, using the extended rat-ear flap model. The flap was either supercharged with both the perforators of the scapular and pelvic arteries, or both scapular and pelvic veins. The results of the study suggests that augmenting venous drainage provides statistically significant improvement (87 percent vs. 51.6 percent) in increasing flap survival, when compared to augmenting the arterial supply. Arterial supercharging provided no improvement in flap survival, when compared to no supercharging (axial vessels + arterial supercharging, 51.6 percent vs. axial vessels alone, 49.9 percent). The results also suggest that providing adequate venous outflow is more important than providing additional arterial blood, and that impaired venous outflow may contribute to some cases of flap failure. However, it should be kept in mind that the best flap survival occurs with both arterialand and venous supercharging.

KEYWORDS

Extended rat-ear flap model - effects of vessel supercharging - flap viability

REFERENCES

• 1 Conoyer J M, Toomey J M. Dorsal skin flaps in rats as an experimental model.  Surg Forum . 1979;  30 510-511
• 2 McFarlane R M, DeYoung G, Henry R A. The design of a pedicled flap in the rat to study necrosis and its prevention.  Plast Reconstr Surg . 1965;  35 177-182
• 3 Fukui A, Tamai S, Williams H B. The importance of venous drainage in rat flaps: an experimental study.  J Reconstr Microsurg . 1989;  5 19-30
• 4 Lee C, Mehran R J, Lessard M L, Kerrigan C L. Leeches: controlled trial in venous compromised rat epigastric flaps.  Br J Plast Surg . 1992;  45 235-238
• 5 Smoot III C E, Debs N, Banducci D. Leech therapy and bleeding wound techniques to relieve venous congestion.  J Reconstr Microsurg . 1990;  6 245-250
• 6 Su C T, Im M J, Hoopes J E. Tissue glucose and lactate following vascular occlusion in island skin flaps.  Plast Reconstr Surg . 1982;  70 202-205
• 7 Roberts A P, Cohen J I, Cook T A. The rat ventral island flap: a comparison of the effects of reduction in arterial inflow and venous outflow.  Plast Reconstr Surg . 1996;  97 610-615
• 8 Ueda K, Harashina T, Oba S, Nagasaka S. Which vessel is more important in the supercharged flap-artery, vein, or both?.  <~>An experimental study. J Reconstr Microsurg . 1994;  10 153-155
• 9 Chen L, Chiu D TW. A successful replantation of rat ear.  J Reconstr Microsurg . 1986;  2 195-197
• 10 Chiu D TW, Ascherman J A, Patsis M C. Rat ear transplantation: a feasibility study.  J Reconstr Microsurg . 1993;  9 33-38
• 11 Chiu D TW, Ascherman J A, Patsis M C. Prolongation of rat ear allograft survival with cyclosporine.  Transplantation . 1993;  56 253-255
• 12 Chiu D TW, Chen L, Chen Z W. Rat ear reattachment as an animal model.  Plast Reconstr Surg . 1990;  85 782-788
• 13 Buncke Jr J H, Schulz W P. Total ear reimplantation in the rabbit utilizing microminiature vascular anastomosis.  Br J Plast Surg . 1966;  19 15-22
• 14 Hirase Y, Valauri F A, Buncke H J. Neovascularized free cutaneous cartilage flap transfer with microsurgical anastomosis: an experimental model in the rabbit.  Ann Plast Surg . 1988;  21 342-347
• 15 Hurn I L, Fisher J C, Arganese T, Rudolph R. Standardization of the dorsal rat flap model.  Ann Plast Surg . 1983;  11 210-213
• 16 Campbell S P, Moss M L, Hugo N E. When does a random flap die?.  Plast Reconstr Surg . 1992;  89 718-721
• 17 Issing W J, Naumann C. Evaluation of pedicled skin flap viability by pH, temperature and fluorescein: an experimental study.  J Cranio-Maxillo Surg . 1996;  24 305-309
• 18 Rajagopal U, Friedman R M, Robinson Jr B J, Rohrich R J. Iloprost enhances survival of axial-pattern skin flaps in an ischemia-reperfusion model.  Plast Reconstr Surg . 1995;  95 884-887