Effect of age upon ischemia/reperfusion injury in rat muscle free flaps

Metabolic and functional changes have been found in tissues of aging man and animals. It is not known if old age has a detrimental effect on the outcome of free tissue transfer or extremity replantation, nor has it been determined if prolonged ischemia may exacerbate such effects. To explore these issues, we utilized a syngeneic rat model of cutaneous maximus muscle transplantation, isolating the effects of flap age and ischemia on flap survival and metabolic function. Flaps were raised in young adult (2-3 months), middle-aged (10-12 months), and old (20-22 months) Lewis rats and transplanted to young Lewis recipients after 1, 6, or 10 hr of room temperature ischemia. Reperfusion periods of 2 hr, 2 days, or 2 weeks were allowed, and flaps were harvested for histologic and histochemical evaluation. Flap weights significantly increased after reperfusion following longer vs shorter ischemia and in the old flaps versus young flaps (for 1 hr of ischemia) (P < 0.05). Histology confirmed a greater extent of interstitial edema in flaps from older rats. Histochemical assessment of muscle dehydrogenase activity (nitroblue tetrazolium staining) demonstrated reduced staining in both the young 10-hr ischemic flaps and in the older 6- and 10-hr ischemic flaps. These results indicate that muscle does not tolerate ischemia as well in older animals, but that a short ischemic interval (1 hr) is well-tolerated.