There seems to be controversy about whether or not the cellophane band actually closes off completely like the ameroid constrictor. Here are a couple of links:
Morris Animal Foundation - Character of Occlusion of Portosystemic Shunts After Cellophane Band Placement AVMA - Journal of the American Veterinary Medical Association - 228(9):1355 - Abstract[B]
Your vet sounds like a good one and confident in his work. Make sure to ask about his success rate. Prayers for your little one
