QS7: Effect Of Static Cold Storage On Vascularized Composite Allografts

PURPOSE: The current gold standard in organ storage is static cold storage (SCS) at 4°C in a preservation solution (UW, HTK). While kidneys can be stored for 24 hours in SCS, Vascularized Composite Allografts (VCA) have been transplanted up to 12 hours in this condition. We aimed to determine the limits of VCA viability with SCS. We used a partial heterotopic hindlimb transplantation model on rodent to assess VCA survival at various durations of SCS. METHODS: Right partial hind limbs in Lewis rats were procured and a 24G Angiocath inserted in the femoral artery. Limbs were flushed with 2ml of heparin saline (100UI/ml) at room temperature and then 5ml of ice cold HTK solution. The limbs were then immersed in HTK in a sterile bag and stored at 4°C for a period of 12(group 1), 18(group 2), 24(group 3), 48 (group 4) or 0 hours (fresh controls Group 5), before microsurgical transfer to the opposite groin. Graft weight was assessed before and after cold storage. At post-operative day (POD) 21, VCAs were harvested for histological analysis. RESULTS: In all groups, there was no significant difference of weight gain in SCS groups after extended SCS times. In group 1 (n=4), 3 rats survived until POD21; clinical evolution showed a limited epidermolysis (<1/3 donor skin surface) in 2 grafts. In group 2 (n=4), 2 rats survived until POD21 without complication. In group 3 (n=6), 3 rats survived until POD21; 1 showed partial superficial necrosis on 50% of the donor skin surface that led to late wound healing. In group 4 (n=4), 3 rats survived; all but one showed extended superficial necrosis over more than 2/3 of the donor skin surface; findings at end of study revealed patent arterial supply but venous thrombosis in 2 rats, inflammatory tissues around the graft and necrotic muscles. There was no difference in the VCA survival rate between the groups 1, 2 and 3 compared to the control group 5. Group 4 demonstrated delayed graft failure. CONCLUSION: SCS provides a safe and simple method of organ storage but is very time limited. Cooling an organ down to 4°C aims to reduce cell metabolism 10-fold but does not make it zero. Hence, VCA hypothermic storage is limited by the remaining metabolism of the skeletal muscle. In our study, rat VCA can be stored in SCS for 24hours without significantly impacting its survival rate but an increase in muscular atrophy and epidermal necrosis correlates with longer hypothermic storage durations. We hypothesize that rat tissues are particularly resistant to SCS thus we need to scale up to a large animal model to better understand ischemic injuries on human tissues.