Efficacy of limb cooling on the salvage of peripheral nerve from ischemic fiber degeneration

Since peripheral nerve has a large ischemic safety factor, hypothermia, by reducing metabolic demands, is potentially an efficacious technique to rescue nerve from ischemic fiber degeneration (IFD). We therefore evaluated the influence of temperature on the severity of IFD resulting from a standard ischemic stress. Ischemia to the left sciatic nerve in the rat was produced by embolization of 2 x 10⁶ microspheres (14 μm) into its supplying arteries. The limb was embolized at three temperatures, 37°C, 32°C, and 28°C and was maintained at each temperature for an additional 4 h. End points, evaluated 7 days after embolization, for the embolized limb were: (1) behavioral scores, 0-11 in increasing limb function; (2) compound nerve action potential of sciatic-tibial nerve;(3) sciatic nerve blood flow (NBF, in mL/100 g/min); and (4) histologic grade, expressed as percentage of fibers undergoing IFD (0 = <5%; 1 = 5-25%; 2 = 26-50%; 3 = 51-75%; 4 = >75%). NBF was reduced in all groups, varying with temperature, and all indices of nerve structure and function were significantly improved with hypothermia. We conclude that hypothermia, easily achievable in a limb nerve, is highly efficacious in the rescue of nerve from IFD. These findings are of clinical relevance.