Determination of a perfusion threshold in experimental perforator flap surgery using indocyanine green angiography

Indocyanine green (ICG) angiography has been used in the evaluation of flap perfusion but the viability threshold has not been elucidated. In this study, we determined the threshold by comparing perfusion, using ICG imaging (SPY imaging system, LifeCell Corporation), to clinical evidence of nonviability in rat abdominal perforator flaps. Abdominal flaps, based on a single perforator, were elevated and re-inset in Sprague-Dawley rats. ICG imaging and clinical assessments were conducted preoperatively, as well as 0, 24, and 48 hours postoperatively. SPY-Q software allowed standardization of the perforator's perfusion for comparison purposes. A total of 278 random percentage measurements were made from postoperative day 0 giving a mean (SE) percentage perfusion of 26.8% (1.6%) and 59.1% (1.3%), respectively, for necrosis and survival (P<0.05). We demonstrate that ICG angiography can be readily analyzed in a perforator flap environment allowing a determination of the perfusion threshold.