IV nutrition. Tpn stands for total parenteral nutrition. Enteral means that the GI tract is used (the patient is eating or tube feeds are being given). Parenteral means that the intravenous route is being used instead. Tpn is used when it's not safe to used the GI tract (for instance, when there's a bowel obstruction) or when the GI tract isn't functioning properly (e.g. Short bowel syndrome).
Intestine failure. Tpn is the primary therapy for intestinal failure - a condition that exists when your intestine cannot provide enough nutrition and fluid to support life. You may be malnourished or dehydrated and require TPN for a short time. However, in certain situations, TPN can be required long term and may be permanent. In those instances, you may consider intestine transplantation.