TPN/PPN Parenteral Nutrition: 5 Pearls Segment

Core IM Podcast

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Time Stamps

• 01:35 PEARL 1: Basics of PN: What makes up parenteral nutrition?
• 06:54 PEARL 2: Indications and Contraindications for TPN and PPN: When should I order parenteral nutrition?
• 13:40 PEARL 3: Complications of parenteral nutrition: What are the common adverse effects of parenteral nutrition?
• 19:41 PEARL 4: Parenteral nutrition myths: What should patients know before they start TPN?
• 23:56 PEARL 5: Recap on Tube Feeds: How do we determine the amount of free water to give out patients on tube feeds?

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Show Notes

Pearl 1: Basics of PN: What makes up parenteral nutrition?

• Total parenteral nutrition (TPN)
  • Purpose: to deliver ALL required micronutrients and macronutrients
  • Composition: mixed with dextrose solution (D5, D10, or D20)
    • Amino acids
    • Lipids
    • Electrolytes
    • Minerals
    • Multivitamins
    • Insulin (sometimes)
      • May be added for patients with hyperglycemia
    • Note: SMOFlipid (Soybean oil, Medium-chain triglycerides, Olive oil, Fish oil) emulsion is a more balanced lipid emulsion to prevent the elevation of triglycerides & LFTs
  • Delivery:
    • TPN
      • Central venous catheter
        • • Port
          • PICC (peripherally inserted central catheter)
          • Tunneled/temporary central line
        • Benefits:
          • Delivers hyperosmolar formulation
          • Helpful when volume of fluid needs to be limited! Ex.
            • Heart failure
            • Liver failure
    • PPN
      • Large bore peripheral IV catheter
        • Given for short durations! Ex. 10 days or less
        • Considerations:
          • Osmolarity
            • Because PPN is given administered through peripheral vein → osmolarity of the solution is limited to 900mOsm/L per aspen guidelines
            • Lower osmolarity = lower calorie and protein content!
          • Volume
            • Cannot give higher osmolarity solution than D5W → large volume administration
              • Limits the amount of calories infused!
            • May not be optimal for patients at risk for fluid overload

Pearl 2: Indications and Contraindications for TPN and PPN: When should I order parenteral nutrition?

• BEFORE YOU ORDER
  • Perform a full assessment to evaluate the feasibility of using enteral nutrition.
  • Dietitians are a great resource for this!
• DECIDING TO ORDER?
  • Indications
    • When enteral nutrition is contraindicated or not tolerated, TPN is an equally safe and effective alternative!
      • Short Term Indications: Unable to tolerate EN or PO → malnutrition
        • Obstruction or ileus
        • Preparation for surgery
        • Severe esophagitis due to chemotherapy
        • Fistulizing diseases requiring bowel rest Ex. IBD
        • Inability to place enteral access Ex. Nasal/Facial fractures
      • Long Term Indications:
        • Not enough absorption capacity
          • Villous atrophy
          • Length of bowel is limited (<200 cm of bowel) due to resections, short bowel syndrome, etc.
            • Note: GLP2 agonists can increase villi → help improve absorption in short gut syndrome
          • Malignant bowel obstruction
          • Severe dysmotility Ex. scleroderma or severe neuromyopathic disorders
      • Contraindications to TPN
        • Working GI tract
        • Infected lines or bloodstream infections
        • Uncontrolled hyperglycemia
        • Severe electrolyte abnormalities
        • Lack of central access
        • Significant volume overload
        • Shock liver
        • Select palliative cases

Pearl 3: Complications of parenteral nutrition: What are the common adverse effects of parenteral nutrition?

• Enteral Nutrition vs Parenteral Nutrition
  • May make little to no difference to mortality in hospital or mortality within 30 days
  • Minimal evidence exists and no studies reported number of ICU free days!
• Complications of TPN have been exaggerated, but some do exist…
  • Bacterial Overgrowth
    • Not using the gut, intestinal atrophy & intestinal permeability –> fermenting inflammatory bacteria overgrow —> bloating & uncomfortable when eat PO
  • Liver dysfunction/Cirrhosis
    • Patients can develop fatty liver disease by six to eight weeks
  • Acalculous cholecystitis/Gallbladder Disease
    • Due to Biliary stasis and Gallbladder distention
      • No PO –> no cholecystokinin release –> no gallbladder contraction –> biliary sludge
  • Catheter-related bloodstream infections (CRBSIs)
  • Commonly coag-neg. staphylococci and Staphylococcus aureus
  • Treatment
    • Removing Line
    • Possible lock therapy
      • High concentration of IV antibiotics is instilled in the line to kill the bacteria that are producing a biofilm inside of the line
  • Overfeeding → hyperglycemia, hepatic dysfunction, infections, respiratory compromise (hypercarbia)
    • Overfeeding is easy with TPN
      • It can explain the results of studies that have shown that TPN increases sepsis!
    • Hypertriglyceridemia
      • Occurs especially with propofol!
        • Note: Hold IV lipids until propofol is discontinued or when triglycerides are <400
    • Early PN trials usually delivered 30–35 calories per kg of body weight,
      • NO longer routinely employed!
    • Past studies allowed for higher glucose goals

Pearl 4: Parenteral nutrition myths: What should patients know before they start TPN?

• MYTH BUSTER 1:
  • TPN does not cause diarrhea since it does not involve the GI tract
    • But patients on TPN may continue to have mucoid stools given cell turnover in the intestine!
• MYTH BUSTER 2:
  • Patients with severe enteropathy require a solute like sugar to help absorb water from the gut
    • Advise these patients to avoid drinking water without solute, it will further dehydrate them!
      • Instead, oral rehydration solutions should be administered
        • Drip drop
        • WHO solution
• MYTH BUSTER 3:
  
  • It is NOT recommended for functional GI patients to start TPN
    • It is important to get GI (or team that would be weaning) involved!

Pearl 5: Recap on Tube Feeds: How do we determine the amount of free water to give out patients on tube feeds?

• How do you know the Caloric Density of Formula?
  • It’s in the number after the name of the formula (calories/mL)
    • Each Tube Formula has a different percentage of free water!
      • 1.5 Formulas → around 76% Free Water
      • 1.0 Formulas → around 84% Free Water
• What’s the difference between free water versus water flushes?
  • Water flushes = additional water to clear the tube periodically, assist with infusing medications and provide total daily fluid needs!
• How do we estimate fluid needs?
  • Free Water Requirement = tube feed volume + free water flushes
  • Different Equations exist!
    • Energy Based Equations
    • Weight Based Equations
      • Uses between 25-35 milliliters per kilogram of body weight
        • 25 for older patients; 35 younger patients
      • Do not forget to include IV medications which may give a patient additional fluid intake!
    • Example Case:
      • An 77-year-old male is receiving Isosource 1.5 tube feeds at a goal of 55 mg/hour. He weighs 88 kg and is 67 inches tall. His total amount of formula in 24 hours is 1320 ml (55 ml/hour x 24 hours).
        • Let’s calculate his FWF (free water flushes)!
          • 1 liter of Isosource 1.5 = 764 ml of water;
            • So in 1320 ml the amount of water in the formula is roughly 1008 ml
              • Math Broken Down:
                • The first 1000 ml of Isosource → 764 ml water;
                • The next 320 ml of Isosource → 244 ml (0.320 x 764 = 244)
                  • 764 ml + 244 ml = 1008 ml
                • We will round that 1008 ml to 1000 ml
            • His total free water requirement should be 2200 mL in one day!
              • Math Broken Down: Use weight based formula for older person
                • 25 ml/kg x 88 kg = 2,200 ml
            • He’s receiving roughly 1000 ml from formula (above)...and so you could give him FWF of 200 ml every 4 hours!
              • Math Broken Down:
                • Free water requirement = tube feed volume + free water flushes (FWF)
                  • 2,200 ml = 1,000 ml + FWF
                  • FWF = 2,200 ml – 1,000 ml = 1,200 ml
                  • Divide 1,200 ml by 200 ml → give 200 ml FWF 6 times a day (or every 4 hours!)
• What is the max amount of FWF?
  • Depends on if the FWF is going into the small bowel vs. stomach!
    • Small bowel
      • Generally max is lower than 200 ml FWF
    • Stomach
      • Can possibly max at 400-500 ml FWF
        • But consider if instilling 2 cups of water in the stomach will be tolerable for the patient!

Transcript

Dr. Shreya P. Trivedi: Welcome to the Core IM 5 Pearls Podcast, bringing you high-yield evidence-based pearls. Today, we’re talking all things parenteral nutrition! I’m Dr. Shreya Trivedi. And I’m joined by

Dr. Hina Mehta: Dr. Hina Mehta, an internist at UT Southwestern

Dr. Margaret Lie: Dr. Margaret Lie, a pulmonary-critical care fellow at the combined Harvard MGH/BIDMC program. In this episode, we’ll be discussing pearls related to total parenteral nutrition (aka TPN) and peripheral parenteral nutrition (aka PPN)!

Dr. Hina Mehta: Test yourself by pausing after each of the 5 questions!

Dr. Shreya Trivedi: Remember the more you test yourself, the deeper your learning gains.

Dr. Margaret Lie: Pearl 1 – Basics of Parenteral Nutrition. What makes up parenteral nutrition?

Dr. Hina Mehta: Pearl 2 – Indications and Contraindications. When should I order and not order TPN and PPN?

Dr. Shreya Trivedi: Pearl 3 – Complications of parenteral nutrition. What are things to watch out for when our patients are on parenteral nutrition?

Dr. Margaret Lie: Pearl 4 – Parenteral nutrition myths. What should patients know before they start TPN?

Dr. Hina Mehta: Pearl 5 – Recap on Tube Feeds. How do we determine the amount of free water to give our patients on tube feeds?

Pearl 1

Dr. Shreya Trivedi: Guys, for me, parenteral nutrition TPN and PPN is something that I just don’t know a lot about. Oftentimes what happens is that I get a page from nutrition, and I just enter whatever orders they recommend. Don’t think twice, but what exactly is in TPN really and what is it really?

Dr. Margaret Lie: Yes Shreya, let’s get into that. To break it down, we talked to Dr. Maria Romanova who is a hospitalist at the Los Angeles VA Medical Center and on the Nutrition Support Team there.

Dr. Maria Romanova: Ahh. TPN. I love my TPN. So what does TPN consist of? Total parenteral nutrition delivers all macronutrients and micronutrients the body needs to sustain itself Specifically it has 10, 20 or 5% solution of dextrose. It has a mixture of essential and non-essential amino acids derived from whey protein and it has triglycerides derived from soybean oil. In addition to it, we add all multivitamins and some micro elements like manganese and magnesium to it. That’s pretty much it. Sometimes insulin is added to the mixture of parenteral nutrition.

Dr. Hina Mehta: So that’s the general gist, but everyday each component of TPN can be personalized to our patients labs and their needs. So, the amount of amino acids, fats, dextrose, and things like vitamins/minerals/electrolytes can change daily.

Dr. Margaret Lie: So all those ingredients are why both the nutrition team and the pharmacy team are so involved in preparing parenteral nutrition for patients!

Dr. Shreya Trivedi: So I guess now that we know a little about what’s in TPN. How is TPN different from PPN?

Dr. Margaret Lie: Well, one thing right off the bat is that TPN and PPN are administered via different types of access. With TPN, a patient would need central access while PPN can be given through a peripheral IV.

Dr. Maria Romanova: You need a central line or a PICC line to deliver a hyper-osmolar formulation, but this is based on dextrose 20 or 10%. If a patient does not have a central access, you can deliver nutrition through a peripheral vein. As long as it’s not that hyper-osmolar. For this, you dilute it in 5% dextrose. That’s the only difference between TPN and PPN, central or parenteral. So how do we use each, right? Peripheral parenteral nutrition is less calorie dense and it requires to be diluted in a larger amount of water, so to say. And so it’s not really good to the patient to be receiving such a large volume of intravenous fluids for a long period of time.

Dr. Shreya Trivedi: Oh! So TPN and PPN are the same exact thing. But, there’s difference in the access and the osmolarities based on how much dextrose is diluted in.

Dr. Hina Mehta: And since PPN is often low osmolarity, the formulas are lower in calories. So with PPN, you would need more volume in order to give you the same amount of calories you’d get with TPN.

Dr. Margaret Lie: And that makes TPN a little better for those people who need less volume. Specifically, those with heart failure or renal failure.

Dr. Shreya Trivedi: Actually, to operationalize that in real life, I’m curious how much volume difference are we talking about here between how much volume we give with TPN and PPN in a day?

Dr. Margaret Lie: I asked one of our local ICU pharmacists, Mehrnaz Sadrolashrafi. She was saying that TPN is typically 1-liter, maybe up to 2-liter, if you add an extra lipid in a 24-hour period, while PPN is typically 2-liters or more.

Dr. Shreya Trivedi: Okay so it sounds like with TPN, maybe we’re saving a patient 1-liter of fluid if possible in a day. So I guess if a patient does have central access, then maybe just reach for that TPN. I guess that also then it makes me curious, what are the times that we should then reach for PPN?

Dr. Maria Romanova: And it’s indicated for short periods really up to two weeks. We usually start when a patient cannot have a central line placed or if we don’t anticipate that the need for parenteral nutrition will be longer than a week or 10 days. So as I mentioned, it’s a lesser, smaller solution and it doesn’t require central vascular access.

Dr. Hina Mehta: So, PPN is typically given for shorter periods of time or if we are not able to get central access.

Dr. Shreya Trivedi: Okay, that makes sense. Alright, this may be a good place to recap. Parenteral nutrition, TPN/PPN, is basically the same thing in that it delivers all the micro and macronutrients a patient may need.

Dr. Margaret Lie: And then for the two types of the parenteral nutrition that we have, the main difference between TPN and PPN are the components, specifically the concentration of the dextrose. PPN has lower osmolarity in order to be safe for peripheral administration through the vein. And with PPN, in general, we are delivering more volume in order to get the same number of calories.

Pearl 2

Dr. Shreya Trivedi: Okay, so now that we know what’s in TPN and PPN. Let’s go over the indications and then the contraindications.

Dr. Margaret Lie: So there are two specific patient populations that need parenteral nutrition – those who only need it for a short period of time and those who need it for a prolonged period.

Dr. Hina Mehta: And Dr. Amelie Therrien, a GI attending at BIDMC with an interest in clinical GI nutrition told us about the typical patients she sees on short term parenteral nutrition

Dr. Amelie Therrien: For the short term, if you have a patient that is very, very, very malnourished that needs a surgery, that needs cancer therapy, sometimes you would get to a better nutritional state by doing TPN rather than to start tube feeds and then it’s going to take longer, especially if they have severe Crohn’s disease and they’re kind of obstructed or if they are in lots of pain.

Dr. Shreya Trivedi: So short term use of parenteral nutrition, it’s going to be mainly patients post-surgery, or those with structural issue, like Crohn’s flare that will likely resolve. But what about our patients who need TPN more long-term? What are the indications for those?

Dr. Margaret Lie: Well, it’s typically for patients who have GI tracts that don’t work properly.

Dr. Amelie Therrien: It’s either because you do not have enough absorption capacity. Either because you’ve got several resections because of ischemia, Crohn’s, children that are born with necrotizing enterocolitis. So if your volume of normal villi that are absorbing or if you have a severe enteropathy celiac disease graft versus host, until that gets fixed, you need to have IV support. So the length of the intestine, if the person has less than 100 centimeters of small bowel or if there is severe villous atrophy.

Dr. Hina Mehta: Yes! Often patients with villous atrophy or short bowel syndrome really need TPN for the long term. But, just a reminder, short bowel syndrome occurs in patients with <200 cm of small bowel

Dr. Margaret Lie: One other thing I thought was cool is the discovery of GLP-2s! Not to be confused with GLP-1s which are used for diabetes and really well-known for weight loss as well. GLP-2 agonists, instead, like Gattex, increase villi and help improve absorption for patients with short gut syndrome, allowing some people to be even weaned off of TPN!

Dr. Hina Mehta: Woah! Move over GLP-1s! Here come the GLP-2s!

Dr. Shreya P. Trivedi: That is really interesting. I honestly haven’t had a patient on Gattex but will look out for– and what an interesting mechanism to actually increase villi. While we’re talking indications, are there any other long-term indications for TPN?

Dr. Amelie Therrien: And then is it moving? Because yes, we have gastroparesis that we can bypass with a J-tube, but there are some people with scleroderma or severe neuro myopathic disorders that things are just not moving. So if they are getting tube feeds or food into their intestine, it’ll just sit there, bloat them, ferment with the bacteria and it’ll not be digested in a good way.

Dr. Shreya P. Trivedi: Okay. So to recap, when we see a patient on long-term TPN, we should ask ourselves two (2) questions. One (1) is the GI tract able to adequately absorb nutrients, whether it’s because of the villi or the length of the gut? And two (2) is that GI tract able to move? And if the answer is no, then parenteral nutrition is likely indicated long term unless something changes.

Dr. Hina Mehta: Okay! So now we know who gets TPN, but who shouldn’t get TPN?

Dr. Cindy Hwang: My first contraindication for TPN is the gut is working, you got to use it. So kind of going back to the tube feeding, right? Is that if it’s working, we are not going to bypass that. We got to keep it working. We’re trying to prevent the atrophy, right? We’re only going to use TPN if their gut is not working.

Dr. Margaret Lie: That’s Cindy Hwang, a dietician from Houston, Texas. It might seem really obvious, especially after our tube feeds episode, but I love emphasizing the point that if someone has a functional gut, it needs to be used.

Dr. Shreya Trivedi: Ahh Margaret, you do love that point. If the gut works, you got to use it! I think for me, my favorite teaching from that episode is counseling patients that if you don’t use the gut, you can have villous atrophy within days.

Dr. Margaret Lie: Yeah! I was really surprised how quickly it could come on. To me, the villi are like skills that need to be practiced otherwise we’ll lose that ability.

Dr. Shrey Trivedi: Yeah. Just like so many things in life. So true. Alright, what are other contraindications to parenteral nutrition?

Dr. Amelie Therrien: Infected line, the fungemia. It’s better for the first 24 hours not to do any parenteral nutrition. The candida, they love the lipids and the nutrients, so it’s good to give a break for the first 24-hours.

Dr. Hina Mehta: So line infections, like bacteremia typically staph aureus or fungemia, should give us a pause.

Dr. Margaret Lie: Yeah, treatment often includes removing the line or something called lock therapy. Lock therapy is where high concentration of IV antibiotics is instilled in the line. This helps to kill the bacteria that produce biofilms.

Dr. Shreya Trivedi: Oh thank you so much for going over that! I can’t believe how many times I’ve ordered lock therapy, but didn’t really understand on how high concentrations of that antibiotic were within the line to “be locked in” there for a little bit and fight those biofilms.

Dr. Hina Mehta: And finally, we have a few relative contraindications to parenteral nutrition, which Dr Romanova refers to as PN.

Dr. Maria Romanova: Those include uncontrolled hyperglycemia, then we put patients on insulin drip, we get the sugars to under 300 and then we can start. Another situation where we use caution with use of PN is fluid overload state like decompensated heart failure or multi-organ failure or giving them too much fluid may cause harm. Those patients should be stabilized and diuresed before PN is started.

Dr. Margaret Lie: One last contraindication is the presence of severe electrolytes abnormalities, which should be corrected before starting parenteral nutrition, especially if the patient is at risk for refeeding.

Dr. Shreya P. Trivedi: Exactly. So let’s summarize this pearl. In terms of indications for parenteral nutrition, in the short term, it’s mostly going to be patients who are in post-op or with a structural issue, like a Crohn’s flare that needs aggressive nutritional support in the short-term. Long-term, it’s going to be patients whose gut is not moving as well or can’t absorb as well. Whether it’s a significant portion of the villi is affected or the length of the gut isn’t as optimal.

Dr. Hina Mehta: Okay! And now let’s recap the relative contraindications that may stop us from starting parenteral nutrition. This includes sugars above 300, decompensated heart failure, and active bacteremia or fungemia.

Dr. Margaret Lie: And my favorite point, the hard contraindication to parenteral nutrition is of course if the gut is working and in that case to use PO options or tube feeds.

Dr. Shreya Trivedi: You do love that point!

Pearl 3

Dr. Shreya Trivedi: Alright, now on to maybe the most relevant part for internists, and the part for me that was the most eye-opening, which is what are the complications we should look out for once our patients are on TPN?

Dr. Amelie Therrien: What I keep saying to patients, because we have some patients who are saying, oh, just put me on IV nutrition that’s going to get my gut at ease, give a break to my gut, but it’s not natural to have parenteral nutrition, like It all goes directly to the liver. And then we see a lot of liver changes. Some people with long-term home TPN can even develop cirrhosis. All of those patients develop fatty liver disease after six, eight weeks.

Dr. Shreya Trivedi: I can’t believe that sugars and fats going through an IV goes directly to the liver and can trigger lipogenesis in less than 2 months!

Dr. Margaret Lie: Yeah, that was really surprising to me as well! So as internists we really need to pay attention to how fats in a formulation may impact our patients’ lipids as well as their LFTs.

Dr. Cindy Hwang: There have been studies that have shown increased LDL, triglycerides and decreased HDL. And so if someone is on this long term, then that might be something to consider to change. There’s another kind of lipid emulsion. So it kind of is more well-rounded of a fat for patients. You’re trying to prevent the increase in the LDL, the triglycerides by balancing out some of the components of the lipid emulsion. It’s called SMOF lipid, – S stands for soybean oil. The M is MCT oil, O is olive oil, and then F is fish oil.

Dr. Shreya Trivedi: Okay, so that’s just great to know that we have options for our patients on parenteral nutrition that possibly prevent some of those parenteral nutrition-associated liver disease (PNALD). Kind of a playoff of NAFLD.

Amelie Therrien: When you eat, there’s a release of cholecystokinin, which makes the gallbladder contract and shoot bile into your GI tract. If all of your meals are from parenteral nutrition and you’re not using your GI tract, there would be some sludge developing in your gallbladder. So people are at risk of developing gallstones, acalculous cholecystitis, regular cholecystitis, if they’re not eating at all.

Dr. Hina Mehta: So what we are saying here is that patients on TPN have sludge build up in their gallbladder because they are just not using it and this leads to a whole host of gallbladder badness.

Dr. Margaret Lie: Another complication that we’re more cognizant of these days is overfeeding patients or giving them too many calories, especially in the ICU.

Dr. Amelie Therrien: In fact too much calories for ICU patients that are ventilated, it can cause hypercapnia and then their ventilation requirement changes because they’re suddenly burning more calories and producing more CO2. If you have an ICU patient that is on propofol on top of the TPN, these are two sources of lipid that can contribute to increased triglyceridemia.

Dr. Margaret Lie: Therefore, the combo of propofol and parenteral nutrition is something to be aware of! It’s pretty crazy how calorie consumption can be related to CO2 production!

Dr. Shreya Trivedi: Yeah. There’s so much ICU medicine I’ve forgotten over the years. For me guys, at least on the floors something that I’ve been seeing more in my day-to-day more frequently is a bunch of patients who have functional bowel syndromes and they often ask for parenteral nutrition. And unfortunately I don’t feel like I have a good spiel on on the risk/benefit on TPN for these patients

Dr. Amelie Therrien: Unfortunately we see lots of people with visceral hypersensitivity IBS that have in fact a GI tract that is still working in terms of motility absorption. And then they’re inpatient and they’re refusing the other options for enteral feeding and everything. And I explained how you need to have food in your intestine for the intestine to keep working. You need to have amino acids like glutamine to feed your intestine, otherwise there’s going to be bacterial overgrowth, there’s going to be more intestinal permeability. And then the person is just going to be super bloated and super uncomfortable as soon as they start eating again. And then it’ll just be a bad vicious cycle with their visceral hypersensitivity.

Dr. Shreya Trivedi: Okay this is so helpful to paint a picture for patients that without using the gut, bacteria can actually overgrow and there is more intestinal permeability with that, and so if patients does eat, even a little bit for just some pleasure, that is not going to be pretty and can kick-off a vicious cycle

Dr. Amelie Therrien: And yes, and when you restart eating, your intestine is very confused to suddenly have that load of osmolarity of that food bolus that comes down and those bacteria will start fermenting and it’ll just worsen the bloating and the pain of the person. And if you stop eating some of the bad fermenting inflammatory bacteria will win over the war against the good bacteria. And that will contribute to having more intestinal permeability. Your intestine is lacking that glutamine, that amino acid that I was saying will be the enterocytes will start dying a little bit.

Dr. Margaret Lie: So, avoiding feeds in a patient with a functioning GI tract can worsen hypersensitivity and also cause bad bacteria to grow, which will cause enterocytes to die and actually worsen bloating and pain!

Dr. Hina Mehta: Oh man, maybe this would be a good place to recap the complications of parenteral nutrition, there are the risks that TPN goes straight to the liver and can cause fatty liver disease and gallstone blockages.

Dr. Margaret Lie: In the ICU, we should be mindful of a patient’s total calories, especially if they’re on both propofol and TPN.

Dr. Shreya Trivedi: And then maybe the most important thing for patients to hear is that if they do take something orally, it can actually worsen some of their bowel symptoms from bacterial overgrowth

Pearl 4

Dr. Margaret Lie: So guys, this is a good place to pause and quickly go over some common misconceptions or myths on parenteral nutrition.

Dr. Amelie Therrien: I have a few people that are coming back to me saying that they have had diarrhea since they started the TPN, and I have to explain that it doesn’t go at all into the GI tract. So it’s not the cause of their diarrhea.

Dr. Shreya Trivedi: So the teaching here is that TPN goes through the IV, directly to the liver through the bloodstream, and it totally bypasses the GI tract. So, parenteral nutrition shouldn’t cause diarrhea.

Dr. Hina Mehta: Wait a minute! So how do patients have a bowel movement if the parenteral nutrition does not enter the Gi tract?

Dr. Amelie Therrien: Technically if you’re not eating, you’ll still have some cells shaving out of your colon, of your small intestine. There’s still like the cell turnover and bacteria. So there’s still some form of mucusy stools that are happening.

Dr. Margaret Lie: The cell turnover in the gut makes a lot of sense! I remember seeing patients who were NPO for days still have bowel movements.

Dr. Shreya Trivedi: Yeah! So true. I guess another thing that this brings up is, I know a good diarrhea history is a whole loaded topic but I wonder if the misconception about TPN causing diarrhea comes from people calling those mucus loose stools “diarrhea”

Dr. Hina Mehta: Yeah that reminds me of the tube feeds episode where the TF does not itself cause diarrhea but the gut atrophy.

Dr. Margaret Lie: Okay so the second misconception is the thought that pure water will be helpful for all patients when they’re dehydrated. But actually, patients with severe enteropathy require a solute like sugar to help absorb water from the gut.

Dr. Amelie Therrien: When you have a severe enteropathy to have pure water, it will not help you, the water to be fully absorbed by your intestine needs sodium, needs sugar. So our patient with short bowel syndrome with severe enteropathy, we tell them to avoid drinking water. They have to drink like orange juice that is a bit diluted.

Dr. Shreya Trivedi: So the dietitian that reviewed this episode did note that the gatorade that’s recommended is usually diluted to lower the sugar content, with ½ tsp of salt is something a little bit closer to what we would give for an oral rehydration solution. I think the big picture takeaway though is if a patient has a severe enteropathy and they’re going to take in something orally for hydration, they do need some solute to go with it.

Dr. Margaret Lie: Okay. Last thing for me is when should we consult or involve GI when starting a patient on TPN? I know that our GI consult list is always so long, and I typically don’t want to bother them.

Dr. Amelie Therrien: I would say that one of the misconceptions is that, okay, we can give to a functional GI patient TPN, and that’s going to be fine. And the GI doctor can wean this off as an outpatient. This is one problem that sometimes we are facing and it’s better to always involve us. If as an inpatient you have a patient without a structural malabsorption or full motility disorder that you want to start on TPN, because after that we are the ones trying to wean the patient down and then the patient doesn’t want to stop.

Dr. Shreya Trivedi: I imagine it’s not fun on the GI end of things when they do the hard job of weaning TPN when they were not involved in the first place with thinking through other options or understanding the symptoms and pathology before to initiation

Dr. Margaret Lie: That’s a great point! Maybe I shouldn’t be so scared to consult GI.

Dr. Shreya Trivedi: Yeah, I’m sure it’s a hospital dependent on who is responsible for weaning. But I agree, it’s better to loop these people in on the earlier sign – they do have a hard job sometimes.

Dr. Hina Mehta: Yep, so to summarize our section on myths and misconceptions, it’s important to know that parenteral nutrition does not cause diarrhea, but patients will likely still have mucus-y like stools from cell turnover.

Dr. Shreya Trivedi: Another one is that in severe enteropathy, the gut still needs solute to fully absorb the water orally. So reaching for some diluted gatorade or some other oral hydration solution may be the way to go. And lastly, it’s probably better to involve GI or whoever is responsible in your hospital system for weaning before starting a patient on TPN

Pearl 5

Dr. Margaret Lie: And that concludes our discussion on parenteral nutrition, but before we go, Shreya, you always mention the importance of spaced repetition.

Dr. Shreya Trivedi: I am a huge nerd about it, and I’m not even ashamed of it! And so of course, now that you brought it up, why don’t we use this as a headspace to cement a couple things from our tube feeds episode and maybe even add on to it!

Dr. Margaret Lie: One thing that I took away was learning that the number behind a tube feed formula indicates the kilocalories/mL, and so if you see 1.5 – 2.0 at the end of a tube feed name, you know it’s more concentrated formula which is good for patients if we want to give less volume.

Dr. Shreya Trivedi: Yeah I didn’t understand those numbers either, and it’s been such an a-ha since the episode, especially since I feel like we’re always thinking about volume status in our patients, right? Whether it’s avoiding the complications of dehydration, and also the other side of things, where we don’t want them to be overloaded.

Dr. Hina Mehta: Yeah! That reminds me of a knowledge gap particularly with free water flushes! When I order tube feeds, there’s typically a default for the volume and frequency of free water flushes.

Dr. Shreya Trivedi: Yeah same! And I just feel like going with whatever generic default our EMR has for free water flushes is probably not right. Now that I think about it more. I’m curious, how can we tailor how much free water flushes a patient needs?

Dr. Margaret Lie: So we sat down with registered dietitians Shaina Shape and Danielle Horn, who work at Northwestern Memorial Hospital in Chicago, Illinois, to help clear up all of this.

Shaina Shape, RD: So there are several different equations for estimating fluid needs. Some common ones would be energy-based equations, so you can think of that as how many milliliters of free water they might need based on their calorie needs. Another common method is more of a weight-based equation, so common weight-based equations be using between 25 and 35 milliliters per kilogram of body weight.

Dr. Hina Mehta: So the 25 ml/kg is more for older patients or patients who need fluid restriction. 35 ml/kg is more for younger patients.

Dr. Shreya Trivedi: Just to play that out, say we have a patient who is 75 kg, depending on if you are using 25 ml/kg or 35 ml/kg, a 75 kg patient would either need 1.8L water/day or 2.6L water/day. But that’s kinda crazy when you think of the default of let’s say 50 ml of free water flushes q6 hours – that’s only like 200ml/day!

Dr. Hina Mehta: Yeah, but I’m wondering how much fluid is in the actual tube feeds and then the free water flushes are just a supplement?

Dr. Shreya Trivedi: Yeah, that’s a good point. I’m jumping too far ahead.

Danielle Shape, RD: If you’re taking into account tube feeding volume tube feeding, each tube feeding volume has a different percentage of free water. So usually 1.5 formulas are around 76%, which is typically the caloric density that we use. If patients are on a lower a 1.0 calorie per milliliter formula. It could be, I think like, 84% free water.

Dr. Margaret Lie: So the percentage of free water in tube feeds can range from 70-84% depending on if the tube feeds are the more concentrated 2.0 version, then you’re thinking maybe it’s 70%, or the less dense 1.0 version.

Dr. Hina Mehta: So if someone’s getting 2 L of tube feeds in a day that have around 75% free water, then they’re already getting 1.5 L in a day of free water just from the tube feeds itself.

Dr. Shreya Trivedi: Okay, so if we go back to our 75 kg patient, who needs anywhere from 1.8L to 2.6L/day in terms of baseline hydration needs, and we now know, thanks to you, Hina, the daily tube feeds is giving them 1.5L of free water. Then yeah, if we’re adding 200ml of free water flushes – say divided 50 ml and it’s q 6 hours– maybe it’s barely meeting that minimum requirement.

Dr. Hina Mehta: Yeah so you don’t have to feel so guilty Shreya! But after doing this math, I would maybe up the flush volume or frequency to prevent dehydration.

Dr. Margaret Lie: One thing to make you feel better is most of our patients on tube feeds are likely receiving IV medications which may give a patient additional fluid intake that we don’t account for.

Dr. Shreya Trivedi: All these are great points. So to recap, what I’m taking away is that baseline hydration requirements for patients, we can start a weight-based approach of 25-35 ml/kg per day. And then, once we get that number, we can subtract the free water that we get from the tube feeds, which is going to be anywhere from 70-84% of the total L/day of tube feeds depending on the concentration. And then also, we can subtract any extra fluids they may be getting from medications. And then, whather number we have leftover is going to be the extra amount free water we want to supplement for free water flushes.

Dr. Margaret Lie: And that’s a wrap for our episode on TPN and PPN.

Dr. Hina Mehta: If you found this episode helpful, please share with your team and colleagues and give it a rating on whatever podcast app you use!

Dr. Margaret Lie: And if you want to learn more, check out the Core IM website and YouTube channel for additional resources.

Dr. Shreya Trivedi: Yeah, we’ll link some of the original clips from the interview with Dr. Amelie Therrien which is so eye-opening. Thanks to our reviewers, dietitians Chelsea Furlan and Juliette Soelberg for reviewing this episode. Thank you to Daksh Bhatia for the audio editing. And as always, opinions expressed are our own and do not represent the opinions of any affiliated institutions.

References

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• Cochrane Library. Enteral versus parenteral nutrition and enteral versus a combination of enteral and parenteral nutrition for adults in the intensive care unit (Review).
• Nowak K. Parenteral Nutrition-Associated Liver Disease. Clin Liver Dis (Hoboken). 2020 Mar 26;15(2):59-62.
• Lindor KD, Fleming CR, Abrams A, Hirschkorn MA. Liver function values in adults receiving total parenteral nutrition. JAMA. 1979 Jun 1;241(22):2398-400. PMID: 108412.
• Gabe SM, Culkin A. Abnormal liver function tests in the parenteral nutrition fed patient. Frontline Gastroenterol. 2010 Jul;1(2):98-104.
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• Berger MM. The 2013 Arvid Wretlind lecture: evolving concepts in parenteral nutrition. Clin Nutr. 2014 Aug;33(4):563-70.

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