Both experimental and clinical evaluation of nitroblue tetrazolium (NBT) as a method of identifying ischemic and necrotic muscle is described. Colorless NBT was reduced to a blue formazin by viable muscle but remained colorless in necrotic muscle. Muscle samples were rated for viability on a scale of 0-100% based on the relative amount of muscle sample that reduced NBT. There was good correlation between gross appearance, distribution of staining, and histologic findings in all nonviable experimental and clinical muscle specimens. All tissue that reacted with NBT proved to be viable histologically. Metabolically active or viable muscle fibers are rich in respiratory enzymes (dehydrogenases). The loss of dehydrogenase activity from ischemic or necrotic muscle can be detected by NBT reduction capacity. NBT technique identified nonviable tissue, clearly showed the even distribution of muscle damage characteristic of electric burns, was useful in defining ischemic muscle prior to obvious necrosis, and was a rapid, simple, and reliable semiquantitative test that can be used intraoperatively.
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