How long will someone stay on tpn?

Until... A patient stays on TPN until they are able to meet their nutritional requirement by eating and any deficit has been made up. Or, until the gut can be used again via a tube placed in the gut, if the patient cannot eat for other reasons.
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.