Central lines and TPN vs PPN


First of all, hi! I've been reading these forums for a long time, but this is my first post. I am relatively new to nursing, and I have a few questions.

I recently started working as a unit secretary, and I was entering some pre-printed orders (no, this facility isn't paperless yet!) into the computer, and I saw the TPN/PPN orders. The order sheet is basically a bunch of boxes where you can have a standard formula or enter certain amounts of the TPN or PPN components. I didn't really understand the difference between the two. I'm too nervous to bother the nurses at work to ask them this, and we're nowhere near this in my classes yet. But I'm very curious. What is the difference between TPN and PPN? Why can you only give TPN through a central line? What would happen if you gave it through a peripheral IV or a midline?

Also, I thought I heard someone say that you can't give vancomycin through a midline. Why is that? If it can go through a central line or a peripheral, why not a midline? Would you be able to give chemotherapy or any other harsh drugs through a midline?

TIA for all answers, and NO, THIS IS NOT HOMEWORK!!!! I'm just too scared to ask anyone at work because I feel like I should be able to figure it out for myself!!! :imbar

Specializes in Telemetry, CCU.

To answer your TPN/PPN question, I am assuming the difference is that TPN stands for Total Parentaral Nutrition while PPN stands for Partial Parentaral Nutrition; total meaning the patient receives no other form of nutrition while partial means they are receiving another source of nutrition probably via feeding tube. If they were receiving TPN, there would be more nutrients in the mixture than PPN, because the doctor factors in nutrients from the tube feeding as well (just guessing here, I've never personally seen PPN orders, just TPN).

As far as it going to the central line and not a peripheral: A central line is placed to end in the superior vena cava. This is a large vessel with a large amount of blood flow, so it can handle caustic fluids being infused into it. A peripheral line is much smaller and has a lot less volume flowing through at any given time, so when caustic fluids are infused, it is very damaging to the vessel wall and can cause a lot of complications. The reason why TPN is caustic is because it contains a lot of packed particles, i.e. glucose and several minerals + electrolytes. Scientifically speaking, the osmolarity is too high for a small vein to handle. There are other drugs that are central line specific.

I don't know the answer to your vanco question because I've never heard that vanco can't be infused into a central line (and that's why its a good idea to look up administration details on IV meds, you don't always know these details by memory). I've never given vanco through a central line, but I'll definitely be looking that one up because a lot of my patients have PICC lines.

Hope I helped to answer your question :)

Specializes in Telemetry, CCU.

I'm sorry, I just reread your post and realized I'm not sure what you are referring to as a "midline". We just call them central lines or peripheral lines, maybe someone else can shed light on what a midline is?


12 Posts

Wow, you're quick. Thanks!!!

At my hospital, if they try to start a PICC but for some reason the tip isn't in the SVC, and they can't advance further, they use it anyway but call it a midline. Since I have no experience working with them, I can only talk about what I have overheard. They say that you can draw blood from a midline, but that it often quits drawing after a relatively short time. After that, they continue to use it to infuse, but not to draw labs. So I guess it's more central than a peripheral stick, but more peripheral than a PICC or other type of central line? Not really sure how they classify that one!!

What you said about TPN/PPN makes sense, and I'm pretty sure that the orders to say Total and Partial. Why, then, can PPN go through a peripheral line? Is it a concentration thing? All I know is that it's a really big deal that you can't give TPN through a midline, and I just can't seem to grasp why that might be. It's probably something really obvious, that's why I'm nervous to ask anyone I know - I don't want them to think I'm stupid!!

Dolce, RN

861 Posts

Specializes in Day Surgery, Agency, Cath Lab, LTC/Psych.

Some facilities have chosen to give Vanco only through PICCs/Midlines/central lines because of extravasation. Vanco is pretty caustic to veins and there have been problems with giving it in little hand veins. You are right about a midline catheter. If a PICC gets shortened it is a midline. Usually it ends in the shoulder area. There is no need for a x ray to confirm placement so it ends up being more cost effective while still accomplishing the goal of having access to a larger vessel.

EmmaG, RN

2,999 Posts

If you'll look at the order sheet at the ingredients of TPN vs PPN, you'll notice that PPN (peripheral parenteral nutrition) has a dextrose of 12.5% or less. Any IVF with a higher dextrose concentration must be given through a central line. (at some hospitals I've worked, the limit was 10%)

A PICC is a central line that is placed peripherally. A midline is a peripheral line. The difference is where the catheter tip lies; a PICC is threaded into the central circulation while a midline ends in the upper arm near the axilla. Because it is a peripheral line, you don't run TPN through a midline.

EmmaG, RN

2,999 Posts

Would you be able to give chemotherapy or any other harsh drugs through a midline?

Depends upon the chemo. Not a vesicant, because of the length of the catheter and where it ends (near the axilla). If you must push or hang a vesicant peripherally, you give it through a small, shorter angio in the forearm, away from any joints. An extravasation in those areas can lead to some horribly disfiguring and disabling consequences...

If a person does not have the peripheral veins to support a safe administration, or if they need a continuous infusion of a vesicant, they must have a central access placed.


70 Posts

Specializes in Neuro/Trauma SICU. Has 7 years experience.

Get the "bag of death" D/Ced. I promotes nothing but infection and sepsis. Sure it is called for in some situations, but when you can, feed the gut with a corpak or NJ tube.

Daytonite, BSN, RN

4 Articles; 14,603 Posts

Specializes in med/surg, telemetry, IV therapy, mgmt. Has 40 years experience.

hi, emsillystudent, and welcome to allnurses! :welcome:

there are weblinks on central lines and tpn as well as other iv information on this thread in the nursing student forums of allnurses:

a central iv line ends in the vena cava of the heart. due to the amount of blood and turbulence created by the action of the heart, iv fluids are immediately hemodiluted and the problem of phlebitis occurring to the vein that the catheter resides in is no longer a problem. tpn generally has a 30% to 50% glucose content. this makes it a very hypertonic solution. this would cause sclerosis and damage to the peripheral veins which is why it is infused through a central line. the highest concentration of glucose that can be infused through a peripheral iv safely is about 10 to 15%.

a midline catheter is an iv catheter that has a cannula that is about 6 inches long. when i worked on an iv team we occasionally used them. supposedly, they are supposed to be able to stay in a vein longer and avoid phlebitis. however, that is not what we found. these midline catheters are generally inserted in an antecubital vein and thread up into the veins of the upper arm. we found that they got phlebitis just as quickly as any peripheral iv so we stopped using them.

you can find the student forums by clicking on the "students" tab above. there is lots of information on the sticky threads (the very first threads listed on any forum).

EmmaG, RN

2,999 Posts

daytonite said:
supposedly, they are supposed to be able to stay in a vein longer and avoid phlebitis. however, that is not what we found. these midline catheters are generally inserted in an antecubital vein and thread up into the veins of the upper arm. we found that they got phlebitis just as quickly as any peripheral iv so we stopped using them.

i agree. imo they are worthless.


12 Posts

Thank you guys all so much for your help! That really does clear things up. I knew that it must be one of the TPN components that caused a problem, I just didn't know which one. And thanks for letting me know what would happen if you did give it through a peripheral or a midline. I find it srange that my facility says no midlines for vanco, but it's ok to do it through a peripheral stick. I guess that must be because in a midline you would be less likely to notice problems right away?? Anyway, thanks again, that clears a lot of things up for me!


38 Posts

Recently we've starting adm TPN through reg IV's. It's not as convenient since you only have the one line to work with so we usually have to start a second line for meds etc.