How is total parenteral nutrition usually given?

Through a vein. Enteral typically means thru your gut or intestine whereas parenteral means any way besides your gut/intestine. Therefore, parenteral nutrition is food typically given through veins. Due to nature of this kind of food, you can't put it thru a small vein like on back of your hand. It has to go thru a major vein, say in your neck, under your collar bone, etc. But since it'll be a while, we use picc.