How often dose a nj tube have to be replaced used 247 only source of nutrition?

7-24 days. An nj or naso-jejunal tube can be left in place anywhere from 7-24 days. More or less frequent tube changes can result in nose bleeds, nasal erosion, pneumonia, and sinusitis. There are many different opinions, but ideally an nj tube is a short term nutrition, and the ideal time to change a tube is around 7 days.
Weeks. Can be left in place until a functional issue arises requiring change. If going to be needed for weeks-->months-->? Then you should discuss with dr about getting a peg or other long term access for nutrition, as if in place too long for specific patient, can cause skin/tissue breakdown in nose.