Welcome to Last Minute Lecture.
This free chapter overview is designed to help students review and understand key concepts.
These summaries supplement, not replace the original textbook and may not be redistributed or resold.
For complete coverage, always consult the official text.
Welcome to the Deep Dive.
Today, we're really wrestling with a fundamental challenge in patient care.
You know, fueling the body when its normal systems are blocked or damaged or just failing.
Yeah, it's critical.
We're jumping into nutritional support systems.
Specifically, what happens when tissue breakdown, that's catabolism, is winning?
And we need to push back to promote anabolism or tissue building.
It really is foundational stuff for anyone in acute care.
When a patient hits malnutrition, meaning their body just isn't getting what it needs, we have to find a way around the problem.
So our mission today is to, well, quickly get clear on the two main delivery methods,
enteral and parenteral nutrition, and maybe more importantly, nail down the pharmacology and the absolutely essential nursing safety checks for each.
Okay, so let's map this out first.
If we're using the body's own plumbing, the GI tract, that's enteral nutrition.
Exactly, enteral is definitely the preferred route.
It just means nutrients are given via the GI tract.
Could be a normal meal, but often, you know, in sicker patients, it's through a feeding tube.
Right, and then if the GI tract is totally offline, maybe after major surgery or pancreatitis, something severe, we have to bypass it completely.
Straight into the blood.
And that's parenteral nutrition.
You'll often hear it called TPN, total parenteral nutrition.
It's the whole package, dextrose, fats, amino acids, vitamins, minerals delivered directly, intravenously into the circulation.
Okay, let's untack this then.
Starting with enteral nutrition,
why is that always the first choice, and who are the patients typically needing these feeding tubes?
Well, first choice, because using the gut keeps the gut lining healthy, and honestly, it's usually safer, and cheaper, too.
Makes sense.
We need tubes when patients can't absorb nutrients properly, maybe their anatomy's altered, or crucially, if their consciousness is depressed, or their gag reflex is shot.
That puts them at huge risk for aspiration.
Yeah, aspiration is always a worry.
Now, in the materials, there's a good breakdown of where these tubes go.
We picture the nasogastric tube nose to stomach, right?
The classic NG tube.
But for longer -term feeding, they're placed surgically.
What's the difference between putting it in the stomach, a gastrostomy, versus bypassing the stomach into the small intestine, a jejunostomy?
Ah, that's key for tolerance.
See, the stomach can handle more complex stuff.
But if the stomach isn't emptying well, or maybe you want to avoid stomach acid, a jejunostomy bypasses it, goes right into the jejunum.
Okay, so route matters.
Once the tube's in, what actually goes through it?
You mentioned basically three kinds of formulas.
Right, three main groups based on how much digestion is needed.
Let's start with the most common ones, the polymeric formulations.
Yep, like Insure or Jevity.
These have complex nutrients, whole proteins, carbohydrates, fats.
They do require a working GI tract to break them down.
But the key thing here is because they're complex, they are less hyperosmolar.
Less hyperosmolar.
Okay.
Okay, translate that.
What does that mean for the patient, practically?
Right, so hyperosmolar means highly concentrated fluid.
If you push that into the gut really fast, it acts like a sponge, pulling water from the body into the intestine.
And that fluid shift is what causes cramping, bloating, and often osmotic diarrhea, probably the most common side effect we see with tube feeds.
Polymeric formulas are gentler that way.
Got it.
So next up are the elemental formulations.
These sound like they're for guts that are really struggling.
That's exactly right.
Think severe Crohn's, short bowel syndrome, pancreatitis, where the gut can barely do any work.
These formulas have pre -digested nutrients.
Simple sugars, little protein fragments like dipeptides or tripeptides, even individual amino acids.
They need minimal, if any, digestion.
Vivinex Plus is a common example.
Okay, and the third type lets you customize things.
Modular formulations.
Yeah, these are pretty neat.
They're single nutrient products, just protein maybe from whey or egg whites or just fat like MCT oil or just carbohydrate powder.
So you add them in.
You add them to a standard formula or even to each other to boost one specific nutrient without overloading the patient with extra fluid or other stuff they don't need as much of.
It allows for really precise tweaking.
This idea of concentration and how fast you give it leads right into the big safety risks with enteral feeding.
You mentioned diarrhea, but also aspiration and dumping syndrome.
Absolutely.
Aspiration pneumonia is, well, it's a nightmare scenario, especially in patients who aren't alert,
feedbacking up and going into the lungs.
Yeah.
Dumping syndrome is kind of the other side of that coin.
It happens when we feed too quickly, often with those intermittent bolus doses.
The concentrated formula basically just dumps into the small intestine way too fast.
And what does that do to the patient?
Oh, it's rough and fast.
Intense nausea, abdominal cramping, they start sweating, get flushed, feel their heart racing.
Sometimes they even pass out, syncope.
Wow.
It's not just feeling bad.
It's a major physiological reaction to that sudden fluid shift and the hormonal changes it triggers.
The fix, slow down the infusion rate, way down.
That balance rate concentration, it also highlights a really critical drug interaction.
You can't just pour meds down the tube with the feed, right?
Definitely not.
Entral feedies can physically block or chemically mess with certain oral drugs.
Okay, like what?
The absolute classic one is Finitoin.
That's Dilantin, the anti -seizure drug.
Tube feeds can seriously reduce its absorption.
Meaning seizures.
Potentially, yes.
If levels drop too low.
We also see feeds inactivating important antibiotics like tetracyclines and the quinolones, Cipro, Glevakin.
So what's the safety rule?
The non -negotiable rule is you must hold the tube feeding for at least two hours before giving these specific meds and then wait another two hours after giving them before restarting the feed.
That sounds like a major scheduling headache on a busy floor.
It absolutely is.
It forces some tough choices about timing and sometimes, honestly, it's easier to switch the patient to an IV form of the drug if possible just to guarantee they're getting it effectively.
That separation is just critical safety pharmacology.
Okay, let's shift gears.
The gut route is out.
We need maximum support.
We're moving to parenteral nutrition, TPN,
bypassing the gut completely.
Right, TPN is basically IV life support for nutrition.
And the first big distinction with TPN is where the IV line ends up.
Is it a peripheral line, PPN, or a central line, CTPN?
This difference is all about the concentration of the feed.
Okay, so PPN uses a regular peripheral vein in the arm.
What's the limitation there?
Exactly.
Peripheral veins are smaller, more delicate.
To avoid serious irritation, flubitis, you have to keep the dextrose, the sugar concentration, really low, usually less than 10%.
So less concentrated means less calories.
Less calories per bag, yeah.
Which means PPN is usually only for short -term use, like less than two weeks.
And because it's dilute, the patient needs to tolerate a lot of fluid volume to get enough calories, often under 2 ,000 kilocalories a day.
Fluid overload can be a risk.
Okay, so for the really high needs or longer -term support, we need CTPN, central TPN.
That goes into a big vein near the heart.
Precisely, subclavian or jugular veins usually.
These are large, high -flow veins, so the concentrated TPN solution gets diluted instantly by the bloodstream.
Ah, so you can ramp up the concentration.
Big time.
With CTPN, we can use dextrose concentrations from 10 % all the way up to 50%, although 25 % to 35 % is pretty common.
Yeah.
This lets us deliver way more calories easily, over 2 ,000, 3 ,000, even 4 ,000 kilocalories a day.
That's essential for hypermetabolic patients, like severe burns or major trauma victims.
But there must be downsides to central lines in such concentrated solutions.
Oh, definitely.
The big risks with CTPN are a much higher chance of serious infection because you have that central line access and metabolic chaos if it's not managed carefully.
Plus, risk of catheter injury itself.
Let's break down what's in that TPN bag.
Three main macronutrients, right?
Starting with amino acids.
Yep, amino acids are the building blocks for protein, crucial for enabalism, for healing tissue.
We talk about essential amino acids, the ones the body can't make, but what's interesting is that essential can shift based on the patient's state.
For example, histidine and arginine are considered semi -central, especially for infants and kids who can't make enough during rapid growth or stress.
Amino acids give you four kilocalories per gram.
Okay, then the main calorie source,
carbohydrates, usually is dextrose.
That's 3 .4 kilocalogram, you said.
Right, dextrose provides the bulk of the energy.
And finally, the most energy -dense part, fats or lipid emulsions, like intralipid or liposin.
These pack nine kilocalories per gram.
A huge amount, yeah.
Now, I usually just think of fats as calories, but is there more to it?
Are they doing something else metabolically important?
Absolutely critical.
Lipids do more than just provide dense calories.
They actually prevent metabolic problems.
If you tried to meet a patient's entire high -calorie need only with dextrose.
Fat idea.
Very bad.
You'd cause severe hyperglycemia and hyperosmolarity.
Using fat emulsions provides calories and essential fatty acids, like limelic acid, with much less impact on blood sugar and fluid balance.
It's a balancing act.
Essential fatty acids.
So if someone's deficient, you might actually see signs.
You can.
Things like hair loss, a characteristic scaly dermatitis, core wound healing.
Seeing those signs tells you their essential fat intake is dangerously low.
Lipids are truly essential.
Okay.
This complexity really highlights the importance of the nursing process.
Careful monitoring seems like everything here.
Starting with assessment, who needs to be involved?
What baseline info is crucial?
First call, always, is to a registered dietician.
They calculate the precise needs.
But from the nursing side, you need a full metabolic picture baseline.
Total protein, albumin, BUN, definitely serum glucose,
kidney function,
liver function.
And allergies, right.
You mentioned those earlier for the modular formulas.
Crucial check before starting anything.
For enteral protein formulas, specifically ask about whey or egg white allergies.
For TP and lipids, the big one is egg allergy, because the emulsion often uses egg phospholipids.
Okay, moving to implementation.
Safety for enteral feeds first.
For NG tubes, number one priority has to be making sure it's in the right place.
Yeah, to avoid aspiration.
Absolutely non -negotiable.
You must check placement before every single feeding and before giving any meds down the tube.
The standard bedside check is aspirating stomach contents and testing the pH.
What's the magic number?
Gold standard is a pH of 5 .5 or lower.
That strongly indicates it's in the stomach's acidic environment.
For those smaller flexible feeding tubes though, an X -ray confirmation after initial insertion is required, because aspirating can be tricky.
But the pH check is the routine go -to.
And then checking gastric residuals, making sure the feed is actually moving through.
Yes, this tells you if the stomach is emptying properly.
Key to preventing backup and potential aspiration.
The rules are pretty specific.
Okay, lay them out.
For continuous feeding,
if you pull back more volume than what was infused over the last two hours, you hold the feed, notify the prescriber.
Got it.
For intermittent bolus feeding,
if the residual volume is more than half of the volume you just put in, you hold that feeding too and check in.
Continuing to feed into a full non -emptying stomach is asking for trouble.
And keeping the tube clear.
Oh yeah, clogged tubes are a nightmare.
Flush, flush, flush.
Use 15 to 30 milliliters of lukewarm water before and after every med, before and after checking residuals, and routinely every four to 12 hours depending on the feed type and hospital policy.
Okay, switching to parenteral safety, TPN risks are systemic infection and metabolic problems.
Exactly.
Infection is a huge risk with that central line being a direct highway into the bloodstream.
And the TPN solution itself being sugary fuel for bacteria.
So strict protocol.
Extremely strict.
Change all the PN tubing every 24 hours or with each new bag.
Always use a filter, typically a 1 .2 micron filter for lipids.
And watch that temperature like a hawk.
Any tempo over 100 .4 degrees Fahrenheit or 37 .8 Celsius needs immediate reporting.
Okay, and the metabolic risk.
You mentioned the high dextrose hyperglycemia.
Big risk, yes.
And often caused inadvertently by us.
Serum glucose monitoring is constant.
But the absolute key rule, never try to catch up the infusion rate if it falls behind schedule.
Why not?
Because suddenly flooding the system with that much dextrose overwhelms the body's insulin response.
It causes hyperglycemia symptoms.
Patient gets really thirsty, peas lot, headache, feels weak, it's dangerous.
Stick to the ordered rate.
And the flip side.
If TPN gets stopped suddenly.
That's rebound hyperglycemia.
Equally dangerous.
See, the body gets used to that constant high dextrose infusion and pumps out insulin to match.
If you abruptly stop the TPN, maybe the line clots or the bag runs out unexpectedly.
Insulin is still high, but the sugar source vanished.
Exactly.
Blood sugar plummets.
The patient gets cold, clammy, dizzy, tachycardia.
It's a rapid crash.
How do you present that?
If TPN has to be stopped suddenly, you immediately hang a bag of 5 % or even 10 % dextrose solution, D5W or D10W, and run it at the same rate the TPN was going.
This keeps the sugar supply going until the next TPN bag is ready or the situation is sorted.
Wow, okay.
And watching for fluid overload too.
Always.
Especially with CTPN volumes.
Monitor intake and output religiously.
Watch for signs like pitting edema, a weak, thready pulse, maybe rise in blood pressure, crackles in the lungs.
Again, maintaining the precise ordered infusion rate is key.
So evaluation.
How do we know if any of this is actually working?
Ultimately, success means and ableism is winning.
The patient feels better, hopefully gains some weight back, looks stronger.
And critically, the lab values improve.
Things like albumin and total protein levels start to normalize.
That tells you you're providing the right building blocks.
So wrapping up, we've really covered the key differences.
Enteral, using the gut, parenteral bypassing it via IV, either peripheral or central, depending on concentration needs.
Right.
We hit the critical need to schedule drugs like Finnytoin and certain antibiotics away from enteral feeds.
And emphasize the huge nursing role in monitoring checking tube placement, watching residuals, preventing dumping syndrome for enteral.
And for TPN, managing infection risk, preventing both hyper and hypoglycemia through careful rate control and monitoring and watching fluid balance.
Exactly.
Those safety checks are paramount.
Okay, so here's a final thought for you, our listeners, to chew on.
We talked about how peripheral TPN is limited, usually under 10 % dextrose, because of phlebitis risk.
Now picture a patient with severe burns or major trauma, someone needing huge amounts of calories for a long time to heal.
What specific patient factors or scenarios would make choosing a central TPN line not just preferable, but absolutely necessary right from the start over trying PPM first?
Think about caloric density, duration, and those risks.
That's a great clinical question.
Really ties the rules to the bedside reality.
Well, thank you for joining us for this deep dive.
And thank you for listening.
We'll catch you next time.