Quantitative assessment of microhemodynamics in ischemic skin flap tissue by intravital microscopy

Skin flaps are susceptible to ischemia, which may result in tissue necrosis particularly in areas deprived of their original anatomic blood supply. Th e pathophysiology of skin flap failure has been debated for many years, but due to methodological insufficiencies, every proposed theory has remained hypothetical. The aim of this study was to gain more evidence for the mecha nisms involved in flap ischemia by assessing quantitatively hemodynamic par ameters such as diameter, flow velocity, and volume flow in the microcircul ation of a flap. To this end the authors developed a new island flap on the back of Syrian golden hamsters that allowed intravital microscopic investi gation. The flap included an extended portion, which was deprived of its or iginal anatomic blood supply. One hour after flap dissection, blood flow wa s 42% to 66% lower in all microvessels in the extended area than in the ana tomically perfused part of the flap (p < 0.05). In the entire microvasculat ure, a significant gradual decline of blood flow was observed over time. An y blood flow reduction was caused to a major extent by diminished flow velo city. At all times, microvascular diameters were slightly larger in the ext ended portion of the flap than in the anatomically perfused portion of the flap. The authors conclude that their new model is a unique tool for invest igating microhemodynamic mechanisms involved in flap ischemia. This study r eveals hypoperfusion of extended flap tissue, which is attributed to dimini shed arterial perfusion pressure but not to vasoconstriction or arterioveno us shunting.