An ischemia-induced model of revascularization failure of replanted limbs

Twenty-five amputated rat hindlimbs were replanted after various periods of warm ischemia. The incidence of limb failure that was due to the no-reflow phenomenon was found to be 0% after 2 or 3 hours of warm ischemia, 50% after 4 hours, and 80% after 5 hours of ischemia. Predictors of the occurrence of no-reflow were the presence of an increased number of venous red blood cell aggregates 5 minutes after replantation, the slope of the tissue pH curve that was recorded for 1 hour after replantation, and assessment of hydrogen washout flow to the foot pad. All limbs had excellent flow immediately after revascularization. The marked difference in flow that was detected 1 hour after replantation between the limb survival group (n = 16) and the limb failure group (n = 9) suggests an ongoing obstructive process. In those limbs that were successfully replanted, an 18% increase in femoral artery flow was found after revascularization compared with a 20% decrease in flow to the muscle and a 3% decrease to the foot pad. This supports the concept that arteriovenous shunting occurs after replantation. The presence of microthrombi that adhere to the vessel wall after replantation correlated well with limb failure. Our observations support ongoing arterial obstruction, arteriovenous shunting, and an altered thrombogenicfibrinolytic system as factors that may be responsible for the no-reflow phenomenon.