Chapter 25: Gastric, Functional & Inflammatory Bowel Disorders

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Welcome back to The Deep Dive.

Our mission, as always, is to get you that critical, actionable intel straight from the source.

And today we're really digging into Chapter 25.

It's all about managing nausea and vomiting and V.

Right, something that sounds simple, but clinically it's really complex.

Exactly.

And we're going to frame this like a quick clinical guide for you advanced nursing students.

We'll cover mechanisms, risks, specific treatments, all audio, no slides needed.

And just to set the stage, remember the causes are incredibly varied, aren't they?

Oh, absolutely.

It could be anything from motion sickness, maybe morning sickness in pregnancy, to serious issues like, say, digoxin toxicity or irritation from antibiotics like erythromycin.

Or even high dose chemo, which is a big one.

A huge one.

And you can't really treat it effectively until you understand the, well, the control center for all this.

Which is the emetic complex, the EC.

That's it.

Think of it as a loose network of neurons down in the medulla.

It's the coordinator, basically.

It takes in all the sensory information and then triggers the physical act of vomiting.

Okay, so it's receiving signals.

Let's talk about those input pathways, because knowing the pathway helps us choose the right drug.

Yeah.

Precisely.

There are several major routes feeding into the EC.

First up is the camoreceptor trigger zone, the CTZ.

Okay.

Now, the key thing about the CTZ is that it's sort of outside the blood brain barrier.

Ah, so it can detect things in the blood directly.

Exactly.

Drugs, toxins, metabolic junk, if it's circulating and nasty, the CTZ picks it up.

Makes sense.

What's the next highway?

Then you've got the visceral afferent nerves.

These are mainly the vagus and splantmic nerves coming straight from the GI tract.

So, like, if the stomach is distended or irritated?

You got it.

Think post -abdominal surgery or even, you know, getting punched in the gut.

That signal goes right up.

Okay.

CTZ for blood stuff, visceral nerves for gut stuff.

What about the brain itself?

Right.

The third major input is from the central nervous system, the CNS.

This involves the tubular system.

That's your balance center.

Motion sickness trigger.

That's the one.

And critically, it also involves the higher centers like the cerebral cortex and the limbic system.

Ah, the psychological angle.

Exactly.

This is where anticipatory emesis comes in, you know, that conditioned response where just the thought or memory of chemo or even just anxiety can make someone nauseous.

Wow.

So you've got dopamine, serotonin, acetylcholine, histamine, all these receptors involved.

It really explains why treatment isn't one size fits all.

It really does.

But before we jump into the drugs targeting these pathways,

why is getting NV under control so urgent?

I mean, aside from patient comfort?

Well, comfort is huge, but the physiological consequences can be really severe, even life -threatening.

You're looking at rapid dehydration, obviously, but also metabolic alkalosis, which throws off the body's pH.

And electrolytes.

Big time.

Significant potassium loss, hypokalemia, and magnesium loss, hypomagnesemia.

Those can cause cardiac issues.

And physical damage too, right?

Absolutely.

Intense vomiting can literally tear the esophagus, those Mallory Weiss tears.

And if someone's had surgery, it can pop stitches, cause wound dehiscence.

It's serious stuff.

So the goal isn't just relief.

It's preventing these major complications.

Yeah.

And the text stresses the timeline.

It's critical.

Your target is control, or at least significant improvement, within about five to 60 minutes of giving a medication.

60 minutes max.

Max.

If you're not seeing results by then, you need to be thinking about Plan B, a different drug or approach.

Don't wait.

Okay.

Time is of the essence.

Let's get into the drugs.

Starting with maybe the workhorses, the ones hitting that dopamine pathway, the phenothiazines, like procolparazine, promethazine.

Right.

Those are foundational.

They primarily work by blocking dopamine receptors, specifically D2 receptors, in that chemoreceptor trigger zone, the CTZ we talked about.

Muting the signal from the blood.

Exactly.

And they also have some anticholinergic effects, which helps block signals from the vomiting center itself and the vestibular system.

And promethazine has an extra trick.

It does.

Promethazine also has significant antihistamine activity, H1 blocking, which gives it a bit broader action, especially if there's a vestibular component.

We see these used a lot different routes too.

A lot.

Oral, IM, IV, even rectal suppositories.

Yes.

But there's a really important caution with the rectal route.

Okay.

You absolutely must avoid rectal suppositories in patients with low platelet counts thrombocytopenia.

The risk of bleeding from the rectal mucosa is just too high.

Good point.

And side effects.

Drowsiness seems common.

Very common.

Sedation and drowsiness.

But the one you really have to watch for, especially with higher doses, is extra pyramidal symptoms or EPS.

Right.

That could be really alarming for patients if they aren't warned.

What does EPS look like?

It can manifest in a few ways.

You might see acute dystonic reactions, like muscle spasms in the neck or face, oculogeric crisis where the eyes roll up.

Scary.

Very.

Or akathisia, that intense inner restlessness.

You might also see Parkinsonian symptoms like a mask -like face, shuffling gait, or a pill -rolling tremor.

It's all due to blocking dopamine in motor pathways.

Okay.

Definitely something to monitor closely.

Now, sticking with dopamine blockers, let's talk metoclopramide, Reglan.

It also hits dopamine, but it does something extra, right?

It does.

And that's key to its specific uses.

Metoclopramide blocks dopamine in the CTZ, like the phenothiazines, but it also acts peripherally in the gut to enhance GI motility.

It increases lower esophageal sphincter tone, speeds up gastric flow, and helps empty the stomach.

So it doesn't just block the nausea signal, it actually helps clear the stomach.

Precisely.

That makes it particularly useful when the nausea is related to slow stomach emptying, diabetic gastroparesis, or post -surgical gastric stasis.

Where just blocking the CPZ wouldn't fix the underlying problem.

Exactly.

You need that prokinetic effect.

Got it.

What's the critical dosing adjustment we need to remember for metoclopramide?

Kidney function.

It's primarily cleared by the kidneys.

If your patient's creatinine clearance drops below 40 mL per minute, you absolutely have to cut the dose by 50%.

Okay.

CRCL less than 40, have the dose.

And the EPS risk?

Still there.

Still there, unfortunately.

It's the most concerning side effect, just like with phenothiazines.

And interestingly, it seems to be a bit more common in children and young adults.

Right.

But the good news is, if EPS does happen with metoclopramide, there's a quick fix mentioned.

Yes.

And this is a vital clinical pearl you need to have in your back pocket.

EPS for metoclopramide can usually be prevented or quickly treated with diphenhydramine.

Benadryl.

Yep.

Good old benadryl.

Usually 25 to 50 mg, IV is fastest, but oral works too.

It often reverses the symptoms quite dramatically.

It's a lifesaver when that happens.

Okay.

Essential safety tip there.

So we've covered dopamine.

Let's shift gears to serotonin, specifically 5 -HT3.

This is where drugs like Ondansetron, Zofran really change the game, especially for chemo patients.

They absolutely revolutionized CINV chemotherapy -induced nausea and vomiting, and also PONV postoperative nausea and vomiting.

How do they work?

They're very targeted.

They selectively block the type 3 serotonin receptors, the 5 -HT3 receptors.

Who are those receptors?

They're found both centrally in the CTZ again, and also peripherally on those vagal nerve terminals in the upper GI tract.

Chemo drugs often cause a massive release of serotonin from cells in the gut lining.

Ah, so the Ondansetron blocks the signal right at the source in the gut, and also in the brain's trigger zone.

Exactly.

And they do it with generally fewer side effects than the older agents, particularly less sedation and almost no EPS risk.

That's why they became first line for CINV and PONV.

Fewer side effects, but not zero.

What do we need to watch for?

The most common things are usually mild headache, maybe some constipation or diarrhea.

Okay.

But the bigger concern, though rarer, is cardiovascular effects, specifically QT interval prolongation on the ECG.

Right, that can lead to dangerous arrhythmias.

It can.

So the crucial point here is electrolyte monitoring.

Before getting a 5 -HT3 antagonist, especially IV, you must check and correct low potassium, hypokalemia, and low magnesium, hypomagnesemia.

Got it.

Correct electrolytes first to minimize cardiac risk.

Now what about agents that aren't primary antimedics but play a key role, like benzodiazepines, lorazepam for instance?

Right, benzos like lorazepam have only mild to moderate direct antimedic effects.

The exact mechanism isn't fully understood, but it seems to act centrally on the vomiting center.

So why use them?

What's their niche?

Their real value comes from their other

anxiolysis, reducing anxiety and amnesia, causing forgetfulness.

For that anticipatory nausea we talked about.

Precisely.

For patients who get nauseous just thinking about their next chemo cycle, lorazepam can be incredibly helpful.

It reduces the anxiety and can help them not remember the unpleasantness quite so vividly.

It breaks that condition cycle.

That makes sense.

Are there contraindications?

Who shouldn't get lorazepam for NV?

You generally want to avoid it in patients with significant hepatic or renal failure because of how it's metabolized and cleared.

And of course, caution if someone is breastfeeding, as it can cause sedation in the infant.

Okay, let's quickly touch on a couple of other classes.

Antihistamines and anticholinergics, like meclizine or the scopolamine patch.

Where do they fit in?

These guys primarily target the vestibular system.

Remember that CNS input pathway?

Yep, balance and motion.

They block acinical choline and histamine receptors right there in the vestibular center and also interrupt some of those visceral afferent signals.

So they're really the go -to drugs for motion sickness.

Like the scopolamine patch for a cruise.

Exactly.

You'd apply the patch behind the ear, usually an hour or two before you need it, and it can last for about three days.

But if you're blocking acetylcholine, side effects.

You get the classic anticholinergic package deal.

Sedation, dry mouth, blurred vision, urinary retention.

You definitely need to counsel patients, especially older adults, who are more sensitive.

Right.

And one more help, Regent.

Corticosteroids, dexamethasone,

methylprednisolone.

How do they help with NV?

It's interesting.

The exact mechanism isn't known.

The leading theory involves inhibiting prostaglandin synthesis somewhere along the line.

But what we do know is that they add significant benefit when used in combination with other anti -medics, especially for CINV.

They have an additive, sometimes synergistic effect.

So rarely used alone for NV, but great as part of a cocktail.

Pretty much.

The main caution is hyperglycemia.

So you need to be careful in patients with diabetes, especially uncontrolled diabetes.

Okay.

That covers the major drug classes.

Let's try to synthesize this.

Imagine you have a patient with mild to moderate NV, not related to chemo.

What's the typical approach like described in table 25 .2 or figure 25 .2?

For that scenario, non -CINV, mild to moderate, you usually start simple.

First line is often a phenothiazine.

Like Promethazine or Prochlorparazine.

Exactly.

Give that a try.

If it doesn't provide adequate relief within that hour time frame.

Pivot quickly.

Pivot quickly to the second line, which would typically be an antihistamere anticholinergic agent like meclazine or maybe diphenhydramine.

Okay.

That seems straightforward.

Yeah.

But CINV is a whole different beast, right?

Yeah.

The approach depends heavily on how likely the chemo regimen is to cause vomiting.

Absolutely.

Chemo regimens are categorized based on their immunogenic potential.

Highly immunogenic means more than 90 % of patients will vomit without preventive drugs.

Moderately immunogenic is 30 -90%.

Low is 10 -30%.

And minimal is less than 10%.

So for those highly immunogenic regimens, you have to hit it hard up front.

What's the standard for preventing that acute CINV, the nausea hitting in the first 24 hours?

The standard of care, the gold standard really, is combination therapy given before chemo starts.

Typically, it's a serotonin 5 -HT3 antagonist PLUS, a corticosteroid.

So ondansetron plus dexamethasone, for example.

That's a very common one.

And the timing is crucial.

You need to give these drugs, usually IV, at least 30 minutes before the chemotherapy infusion begins.

Prophylaxis is key.

Prophylaxis.

Right.

Get ahead of it.

Now what about delayed CINV, that nausea creeps up a day or more later, especially common with drugs like cisplatin?

Yeah, delayed N -V is common and often involves different mechanisms than the acute phase.

Maybe less serotonin release and more substance P or motility issues.

The 5 -HT3 antagonists aren't usually the best choice here.

So the go -to combo changes.

What does table 25 .3 suggest is most effective for delayed?

For delayed CINV, particularly after high -risk chemo, the evidence points towards a combination of metaclopramide plus dexamethasone.

Bringing back metaclopramide for its prokinetic effect, maybe?

That's likely part of it.

And you'd continue this combination for maybe three to four days after chemotherapy finishes to cover that window of risk.

It really highlights how you need different tools for different phases of CINV.

Shifting focus, slightly special populations.

What are the key considerations for kids?

Two main things stand out for pediatrics.

One, they dehydrate much faster than adults, so uncontrolled vomiting is even more dangerous.

And two, they seem to be significantly more susceptible to those extra -pyramidal symptoms, EPS from phenothothiazines and metaclopramide.

Even at lower doses?

Even at standard low doses, especially if they also have some sort of acute viral illness going on.

The risk just seems higher.

You have to be extra vigilant for dystonia or akathisia and kids getting these drugs.

Good to know.

What about N -V -P nausea and vomiting in pregnancy?

Safety is the absolute top priority here.

Paramount.

Always start with non -drug measures.

Dietary changes, ginger, acupressure bands.

Right.

If pharmacotherapy is needed, the first -line recommendation is pyridoxine, which is vitamin B6.

Vitamin B6.

Yep, either alone or sometimes combined with an antihistamine called doxylamine.

That combination is actually FDA -approved for N -V -P.

Ginger supplements also have decent evidence for reducing symptoms safely.

What about the other antimedics we discussed, like phenothiazines or undansetron?

Are they safe in pregnancy?

The data is generally reassuring for phenothiazines and undansetron, although there have been some conflicting studies causing debate, especially with undansetron in the first trimester.

They're usually considered second -line if B6 -doxylamine fails.

Okay.

Are there any classes generally considered unsafe or best avoided?

Yes.

The ones to steer clear of, if possible, due to potential risks of malformations or fetal complications, are the benzodiazepines and, increasingly, cannabinoids.

Got it.

Avoid benzos and cannabinoids in pregnancy for N -V -P.

Finally, how do we actually know if our treatment is working?

How do we monitor effectiveness?

It's a mix of objective and subjective.

Objectively, you can track the frequency of vomiting episodes, maybe even try to quantify the volume if possible.

Okay.

But subjectively is often more important for nausea.

You need to ask the patient.

Use a simple scale, like 0 to 10, where 0 is no nausea and 10 is the worst imaginable.

Ask them to rate it before and after the medication.

So tracking the numbers, but also really listening to the patient's experience.

Exactly.

Their reported relief is a primary outcome.

As we wrap up, what's one crucial patient education point that every advanced practice nurse should nail?

Beyond explaining why they're taking it, make sure they understand how and when.

Is it scheduled to prevent nausea, like before chemo, or is it PRN, take as needed when symptoms start?

That distinction is vital for effectiveness.

Scheduled versus PRN.

Clear instructions.

And definitely counsel them on the main side effects, especially sedation, don't drive if you feel drowsy, and the possibility of those movement side effects, the EPS.

Knowing what might happen makes it less frightening if it does occur.

Informed patients are empowered patients.

Fantastic.

Well, that was a really thorough walkthrough.

We've navigated the emetic complex, looked at the receptors, covered five major drug classes, and mapped out strategies for CINV, non -CINV, and special populations.

We covered a lot of ground.

And hopefully it helps you see why managing NV often requires combination therapy.

That emetic complex is just loaded with different receptors.

Dopamine, serotonin, histamine, acetylcholine, substance P.

Right.

Multiple potential triggers.

Exactly.

So hitting just one pathway might not be enough.

The real art is choosing agents with different non -overlapping mechanisms to block multiple input signals simultaneously.

That makes perfect sense.

Thinking about that complexity and the need for multi -target approaches is a great final thought.

Hopefully a useful one for practice.

Absolutely.

Thank you so much for joining us on this deep dive into the pharmacotherapy of nausea and vomiting.

We truly hope this gives you the clinical insights you need.