Notes from the Video

What am I going to learn in this lesson?

How do you order total parenteral nutrition?

How do you provide your patient with the nutritional supplementation that they're gonna need to get ready for or recover from surgery, injury or trauma?

Goals for Today

1.).  Learn the indications for total parenteral nutrition

2.). Know the difference between peripheral parenteral nutrition and total parenteral nutrition

3.). How do you design a basic TPN solution

Why is it important to know this?

First, it's critically important to understand nutritional assessment and determine if your patient is a higher risk for infectious mortality and increased length of stay and other complications.

Second, when we're designing a TPN solution we need to know if and when your patient will need supplementary nutrition, whether it will have to be enteral or parenteral and when it's parenteral you should have a really good idea of how that TPN solution is structured so that you can have an intelligent and educated conversation with your nutritionist in the hospital or if you have to write that yourself there are a couple of really good references for today.

References

1.). ESPEN Guidelines most recently published in 2017 and in this edition they really go through a nice discussion of Enhanced Recovery After Surgery (ERAS) approach and providing preoperative nutrition as well as limiting fasting, how a preoperative carbohydrate drink affects your protein metabolism and your glucose levels and in addition the guidelines also go through the nutritional assessment and everything you need to think about when you're providing nutrition for your surgical patient.

2.). The Hitchhiker's Guide to TPN and it makes it very clear with respect to the nutritional assessment and then how to design your TPN, think about the different solutions, different concentrations, the different additives, basically everything you need to know to start thinking about how to put that TPN solution together.

When is TPN indicated?

• Impaired GI function or unable to receive and absorb enteral feeding for approximately seven days
• Undernourished patients in whom enteral nutrition is not feasible or not tolerated
• Combination of enteral feeding with supplementary parenteral nutrition is your first choice

This last point is when you need to think about that combination of enteral + parenteral.  This is often the case after major abdominal surgery where the patient is tolerating a little nutrition but not enough.  If a patient's not able to take in 60% of their calories enterally then you want to add in a supplementary parenteral nutrition.

Every time you're rounding on your patient you should be saying "okay are they taking in enough calories" NOT "are they taking in just enough food"!

If they've taken in some more broth today and a couple of pieces of white bread that's not going to cut it so you really have to think about not the volume of enteral intake postoperatively but the nutritional quality of that internal intake and are they taking enough calories orally or do they need IV supplementation.

Now everybody likes lists, so we're going to go over here to talk about a list of indications for TPN and these are these are little clinical vignettes but on exams in the oral discussions, roundsman ship, when you're asked about what are some indications for TPN here are a few:

• Massive small bowel resection (neonates necrotizing enterocolitis or malrotation or atresia) and short gut syndrome
• Radiation enteritis
• High output enterocuteaneous or enteroatmospheric fistula (>500ml/d)

What about peripheral parenteral nutrition?

Peripheral parenteral nutrition is typically indicated for a younger healthier patient, they're going to need short-term supplementation for less than a couple of weeks, the nutritional needs are less than 1800 kcal/d, and they have good peripheral access.

There's a good rule of thumb and that's say if you've had to change the IV two to three times in the first couple of days of admission those are not good candidates for peripheral parenteral nutrition.

Also it's important that these patients don't have any fluid restriction issues, usually with PPN you're running this at a higher volume so patients with cardiac, respiratory, or renal failure are not good candidates for PPN. 

These are also lower osmolality solutions so 600-900 millimoles (compare that to plasma at 274 millimoles or TPN at over 1300 millimoles.)

These are less caustic to those peripheral veins that have lower blood flows  this is like I said limited use in because of the lower osmolality.

How is TPN different that PPN?

Total parenteral nutrition a little bit different as it's given via central access and these are the central veins they have usually greater than 6 liters per minute of blood flow.

If parenteral nutrition is necessary TPN is flexible if you need that minimal volume or contracted volume because they are higher osmolarity solutions and can be concentrated even further.

What are the components of TPN?

Now let's get in to each of the different energy components of TPN which include carbohydrates, protein and lipids.

Carbohydrates

Now first going through carbohydrates, remember, humans are carbohydrate burning machines!

Carbohydrates are the majority of the energy that you need to provide your TPN solution this works out to be about 60% of the total kilocalories that you need for the day.

There are limits to this there is a ceiling of total carbohydrates before it gets dangerous and that ceiling is  7.2 grams per kilo per day.

If you go higher than that you risk hyperglycemia and all of its complications, you also risk hepatic steatosis and liver damage so that remember that amount of dextrose that you can add has a ceiling of 7.2 grams per kilo per day!

Lipids

Lipids are an incredibly important source of energy!

Lipids come as intravenous fat emulsions and you may see this a couple of different ways in the hospital:

You'll see this as that little bag of white fluid that's piggybacked on to either peripheral parental nutrition or total parenteral nutrition and this is 20 to 30% of your total kilocalorie requirement.

Commercially available solutions which would be intralipid or liposyn and they contain vitamin K.

Also one thing to keep in mind with intravenous fat emulsions is there are different types of fats including omega 3 and omega 6 fats.

What is the difference between omega 3 and omega 6 fats?

Omega 3 fats, your fish oils, are immunosupportive fats

Omega 6 fats are immunosuppressive and pro inflammatory.

If we look back at the history of TPN we know that the initial fats that we used were really pro-inflammatory, for example cottonseed oil, and even now most of the content of intralipid or liposyn, the commercially available lipid solutions contain soybean oil which has omega 6 fatty acids and is pro inflammatory. 

Some of the newer lipid formulations like SMOF (Soybean, medium chain triglycerides, olive and fish oils) and Omegavan (Omega 3) aim to reduce the pro inflammatory nature of the lipid formulations.

When does altering the lipid content of TPN become important?

If I am taking care of a neonate who has short gut from necrotizing enterocolitis or an atresia or malrotation volvulus and they are going to need their central venous access and TPN for a long time I want to be sure to use an omega 3 based lipid formulation like SMOF or Omegavan to prevent against TPN cholestasis and liver failure.;

Protein

A basic protein requirement is 1.5g/kg/day.

If we take specific groups of patients like burn patients and they're giving up a lot of protein they might need more protein, other patients, may be a uremic patient might

need less protein so you want to think about how much protein you're giving but 1.5 grams per kilo per day is a great place to start.

Branched chain amino acids are important source of fuel and injury recovery, providing a source of glutamine and alanine for ongoing recovery.

How do we design a basic TPN solution?

If you need a refresher on how to estimate fluid requirements and energy requirements definitely check out my video on TPN Basics and you will know it cold!

Let's say we have a previously healthy 70 kg male with a gunshot wound to the abdomen, he's left in discontinuity and needs TPN.  It's been a few days and you are confident he is going to need supplementary nutrition.

First, what are his fluid requirements?

So first let's talk about his fluid now we can easily go through and talk about what we think his fluid needs are and with a 4-2-1 rule we come up with 110ml/h or 2440ml for the day.

Remember, you're going to have to take into account his fluid balance, intake and output (nasogastric tube output, urine output, wound vac output, etc) when calculating his fluid needs.

Now, how about energy?

First we're going to estimate his kilocalorie requirement at 30kcal/kg/day, at the upper end of the "healthy" patient given his level of injury.  That will be 2100kcal/day of an energy requirement.

Start with lipids...

Remember, lipids are going to be 30% of our daily caloric need, if we calculate that for our 70kg male it comes out to 630 kilocalories of lipid.

If we use a 10% intralipid solution it is going to be about 1.1kcal/ml of solution so we will need 572ml of a 10% intralipid solution.

Why a 10% intralipid solution?  In this case we're not fluid restricted, but if we were, perhaps in the case of anasarca or in cardiac failure or adult respiratory distress syndrome (ARDS) then we could use a 20 or 30% solution which would be more concentrated and less volume.

Then the protein requirement...

We are going to start with 1.5 g/kg per day, that's 105 grams of protein total in our TPN.

If we use a 8.5% aminosyn solution that is 85g of protein per liter and if we do the math we're going to get 1235ml of an 8.5% aminosyn solution.

Now on to carbohydrates...

The best way I've found to calculate the carbohydrate requirement is to subtract the lipid and protein volume from the total volume and then subtract the lipid and protein

calories from the total calories.

In our example we are going to need an additional 633ml of volume and 1050 additional kilocalories from carbohydrate.

The carbohydrate we like to use is dextrose and that's 3.4kcal/g.

So if we know this we can divide the total calories divided by 3.4 (1050/3.4 = 309g dextrose).

309g dextrose/2440ml = 12.6% dextrose solution.

Putting it all together!

A 2440ml solution of TPN with 30% of calories from lipid, approximately 50% of calories from carbohydrates and 20% of calories from protein gives us...

572ml of a 10% intralipid solution

1235ml of an 8.5% aminosyn solution

633ml sterile water with 309g dextrose giving a 12.6% solution

What about electrolytes and other additives?

Now it's important to know the highs and the lows of each of your electrolytes so sodium, potassium, bicarbonate, magnesium, phosphorus, and calcium must know all those.  We're going to go through them in detail  in the next video on fluid and electrolytes but here I just want to give you a starting range that you can see int he video..



What are some other additives that are important in TPN?

• Increased omega-3 polyunsaturated fatty acids
• Additional glutamine and arginine supplementation can improve outcomes
• Vitamins and essential minerals every day
• Insulin, consider adding one to two units per 10 grams of carbohydrate for patients with persistent glucose levels over 200 (in our patient we were using 309 and you would want to use about 30 units of insulin in that patient to start and that would give you a good glucose control if indeed your glucose levels were over 200 a day)
• H2 antagonists to prevent GI ulceration
• Iron supplementation in patients who need that extra mineral

With TPN there are a lot of different modifications you can make and it can make your head spin.  There can be alteration in the amount of fluid (for example you may want "minimal volume TPN" in patients with heart failure), amount of energy, electrolytes, vitamins and minerals and of course all of the different additives.  It's important that you consult and work with you nutritionist, whether it's on the ward or in the ICU to optimize the care of your patient.

What About Vitamin deficiencies?

What TPN talk would be complete without talking about all the nutrients and the deficiencies? 

 It's important to remember that each of these vitamins has an associated deficiency and this is like testing gold, every test you take in medicine is going to at least have one question on this and usually a couple so the important ones:

Thiamine, folate, niacin and your vitamin b12 then of course all the fat soluble vitamin deficiencies.  Definitely review the cheat sheet provided in the video for all of these!

You'll also want to be confident on all of the mineral deficiencies as they come up very frequently!