Colgajos

|17 Flap Physiology |

|Nicholas B. Vedder MD ||WHAT IS A FLAP? |

|Flaps are the essence of plastic surgery. The ability to successfully conceive, design, execute, and manage a flap is what defines a plastic surgeon. What distinguishes a flap from a graft is |
|anintrinsic blood supply that is responsible for a flap's viability; a graft must rely on diffusion until its vascularity becomes re-established. An intrinsic vascularity confers tremendous |
|flexibility and potential, allowing a flap to supply critical vascularized coverage to complex defects and to restore form and function in nearly unlimited ways. Because the viability of a flap|
|depends onits intrinsic vascularity, fully understanding and being able to optimize the vascular physiology of a flap can make the difference between success and failure. |

|As in all tissues, the vascular supply of a flap includes both macrocirculation and microcirculation components. Both of these are subject to intrinsic and extrinsic factors that can |
|dramaticallyinfluence perfusion and hence viability. The anatomy of the macrocirculation is used to define and design a flap. The major arterial inflow and venous outflow of a flap constitute |
|the foundation from which the microcirculatory beds then provide nutrition and oxygen and carry away carbon dioxide and waste products, thus forming the basis of cellular metabolism throughout |
|the flap. It is atthe microcirculatory level-the arterioles, capillaries, venules, and arteriovenous anastomoses-where this exchange occurs and where most of the control of perfusion occurs. |

|Taylor1-5 has eloquently demonstrated that the blood supply to potential flaps involves a continuous three-dimensional network of vessels not only in the skin but also in all tissue layers. The|
|anatomic territory of asource artery in the skin and deep tissues, in most cases, gives rise to what has been described as the angiosome concept. Arteries closely follow the connective tissue |
|framework of the body. The primary supply to the skin is by direct cutaneous arteries, which vary in caliber, length, and density in different regions. This primary supply is reinforced by |
|numerous small indirectvessels, which are terminal branches of arteries supplying the deep tissues. Careful anatomic studies have shown an average of 374 major perforators in the human |
|subject, revealing that there are many more potential skin flaps yet to be defined. The angiosomes defined in this way are the tissues available for composite transfer. |

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|One of the primary functions of skin is thermoregulation, which is accomplished through the regulation of skin blood flow. Heat is dissipated by increasing skin blood flow and is conserved by|
|decreasing skin blood flow. The primary...