60 | The hard facts on constipation: how to give great care to your backed-up patients

PodcastGastroenterology
Written By Laura Jones

We’ve all seen those crispy senior cats admitted with severe constipation and dehydration.

 

And even worse, ones who get so constipated that they just can’t defecate at all, leaving us to have to do it for them.

These patients are pretty miserable - often really uncomfortable, nauseous, anorexic and markedly dehydrated - and they need a lot of support from us. So, how can we best give this support? Let’s start by looking at why our patients get constipated and what happens when they do.

Is constipation truly constipation? The answer is… not really.

Without soapbox Laura coming out again, most of our constipated patients are actually obstipated - similar, but not exactly the same condition.

Constipation is the term used to describe infrequent or difficult defecation, whereas obstipation is a severe form of constipation where patients become entirely unable to pass faeces. 

Obstipation usually occurs due to faecal impaction within the colon. Over time, this impaction causes the colon to dilate and enlarge as the muscles in the colonic wall work less effectively. This is megacolon, a relatively common condition in cats.

Ok, so many of our constipated patients actually have obstipation - where they can’t defecate at all. But what causes chronic constipation and obstipation in our patients?

Like so many other medical disorders, there are many different causes. These include:

  • Inability to pass poorly digested firm faeces (e.g. containing hair, bones or foreign material such as cat litter in a cat with pica)

  • Dehydration or a lack of water intake causing hard faeces

  • Reluctance to defecate (e.g. due to pain on defecation, stress, or litter tray aversion)

  • Compression causing colonic narrowing from previous pelvic fractures, enlarged lymph nodes, an enlarged prostate, colonic stricture or mass.

And what about megacolon?

Megacolon is generally seen in cats; in most cases, it’s idiopathic (we don’t identify a specific underlying cause). We suspect these cases are caused by defects in the neuromuscular junction within the colon - the areas where nerve signals are transmitted to cause peristalsis. 

Hypothyroidism, dysautonomia, spinal cord lesions, pelvic nerve lesions and some electrolyte abnormalities can also impact neuromuscular function within the colon, contributing to constipation, obstipation and even megacolon in severe cases.

Several medications can also contribute to constipation in our patients through different mechanisms depending on the individual drug. These include:

  • Opioids which slow down GI motility and can, therefore impact the frequency of defecation

  • Diuretics, which promote water reabsorption, potentially leading to firmer faeces

  • Anticholinergic agents (e.g. atropine, glycopyrrolate), which block nerve signals reaching the muscle in the GI tract, reducing peristalsis

Which patients develop constipation, obstipation and megacolon?

Any patient can become constipated, though chronic constipation, obstipation, and megacolon are all more commonly seen in cats. 

It is described more frequently in male cats than in females and more commonly in domestic shorthair, domestic longhair, and Siamese breeds than others. 

In one study, the mean age was reported to be 5.8 years, though this varies widely. We see constipation frequently in many senior cats, likely because of so-called ‘senior diseases’ like chronic kidney disease, which causes dehydration (and therefore constipation). However, idiopathic megacolon is generally seen more frequently in adult and mature adult cats rather than just in seniors.

Ok, that’s what constipation, obstipation, and megacolon are, why they occur, and which patients we see them in. 

But how do they impact (no pun intended!) our patients, and what signs do we see?

Regardless of the cause, constipation, obstipation, and megacolon are all disorders that significantly impact our patients. Depending on the severity of their constipation/obstipation, our patients present with:

  • Infrequent defecation or complete inability to defecate

  • Tenesmus (straining)

  • Abdominal distension

  • Abdominal pain

  • Anorexia

  • Lethargy

  • Vomiting

  • Dehydration

  • Weakness

If the patient has compression or narrowing of their colon/rectum, for example due to a stricture or mass partially obstructing the lumen, they’ll often pass flat, thin, ‘ribbon-like’ faeces.

Some patients can actually pass small volumes of diarrhoea despite also being constipated - making their clinical signs hard to interpret initially. This is usually seen where the impacted faeces irritates the colonic wall. Haematochezia (fresh blood in the faeces) can also be seen due to colonic irritation.

Physical examination often reveals a large amount of faecal material on abdominal palpation. It’s essential to perform a neurological examination and a rectal palpation to identify underlying causes. Often, thorough abdominal palpation and rectal palpation need to be performed under sedation or general anaesthetic, as these patients are incredibly uncomfortable (and will likely need sedation or GA for an enema anyway).

So you’ve examined your constipated/obstipated patient. How do we diagnose them? What do we do next?

Any patient with recurrent or severe constipation should have general bloodwork and urine analysis performed to assess overall health and look for contributing diseases. These tests include:

  • Full biochemistry including total T4 and electrolytes

  • Complete blood count

  • +/- FeLV/FIV if not already known

  • Urine analysis including specific gravity, chemistry/dipstick and sediment examination (+/- protein:creatinine ratio and culture if indicated depending on the individual patient)

  • +/- Blood pressure if indicated (considering that many senior patients, or CKD patients, may be at increased risk of systemic hypertension)

What about diagnostic imaging?

After our initial tests, it’s time to think about imaging. Abdominal radiography is indicated in all constipated/obstipated cats. This allows us to detect impacted faeces and colonic dilation and assess how severely impacted our patient is. It also assesses the lumbosacral spine and pelvis, for example, looking for poorly healed fractures, lumbosacral disease, or spinal deformities (common in Manx cats).

An abdominal radiograph from a 6-year-old FN DSH presenting with obstipation and tenesmus. She was diagnosed with megacolon and, after poor response to medical management, had a subtotal colectomy. She is now doing well.

We can use these X-rays to differentiate between megacolon and obstipation by measuring the widest point of the colon and comparing it to the length of the 5th lumbar vertebrae. To do this, measure the widest point of the colon and divide by the length of L5. If your result is greater than 1.48, your patient has a megacolon; if it’s below 1.28, their colon is normal.

Usually, after these X-rays have been taken, we perform an enema under that same anaesthetic. After this, we should repeat their imaging to assess response and ensure our enema has removed sufficient impacted material.

What other diagnostic tests might we perform?

Depending on the underlying cause of our patient’s constipation/obstipation, we may need to perform additional tests. These include:

  • Colonoscopy to visualise the colonic lumen, identify masses or strictures, and take biopsies where needed (we can also dilate strictures endoscopically using a balloon catheter)

  • Histology of the colon in megacolon patients requiring surgical management (subtotal colectomy)

  • Thyroid testing to look for evidence of hypothyroidism (e.g. free T4, TSH).

Ok, so that’s diagnosis taken care of - but how will we manage these patients?

Managing chronic constipation/obstipation and megacolon isn’t always easy. It requires a multimodal approach: targeting nutritional support, ensuring sufficient hydration, maintaining GI motility and softening faeces alongside providing supportive care.

Some megacolon patients won’t respond to these medical interventions alone and will require surgical management via a subtotal colectomy - we’ll dive into medical treatment first and then chat more about surgery later in the episode.

Let’s start with nutrition

Like all of our medical patients, nutrition is essential in managing constipation/obstipation. Here’s what we need to consider when feeding these patients:

Fibre supplementation.

Many patients with constipation improve when dietary fibre is increased, though we mustn’t increase this excessively, and we feed the right types of fibre. Increasing fibre intake typically increases faecal water content, motility and intestinal transit rate while acting as a bulk-forming laxative.

In patients with some degree of colonic motility, we should aim for a crude fibre content of at least 7% (dry matter basis) with a mix of soluble and insoluble fibre. 

However, as the patient’s constipation becomes more severe and they develop megacolon, fibre supplementation won’t stimulate the colon effectively and can instead worsen obstipation. These patients should have lower dietary fibre - a maximum of 5% (DMB) of their diet.

Because we can easily unbalance a diet by adding too much additional fibre, it’s preferable to reach for a therapeutic fibre-enhanced diet. That way, we can ensure our patients still receive complete and balanced nutrition.

Digestibility and energy density

Obstipated and megacolon patients require a highly digestible and energy-dense diet to ensure adequate nutrition while minimising faecal mass.

It’s also important to note here that fibre is an energy-dilute nutrient - the higher the fibre content in a patient’s diet, the lower the energy density will be. Another reason we don’t want to feed high-fibre diets to megacolon patients is that we’ll have to feed a greater volume of food, resulting in more faeces being impacted within the colon.

And then there’s hydration

We know that dehydration is common in constipated, obstipated, and megacolon patients. Water is a key nutrient, and its intake is often overlooked - in the hospital, we can easily correct dehydration through intravenous fluids, but every effort should be made to continue increasing water intake and supporting hydration at home, too.

Providing multiple water sources, using hydration support products, feeding a wet diet (if possible) and adding water to the patient’s food are all useful strategies for clients to use at home to maintain hydration, and the veterinary nurse or technician is ideally placed to educate and support clients as they implement these changes.

In the hospital, it’ll also be down to us to assess the patient’s hydration status regularly, working with our vet to adjust fluid rates as required depending on the patient’s clinical signs and vital parameters.

Let’s talk laxatives.

The most common medications we reach for when managing our constipated, obstipated, and megacolon patients are laxatives. Depending on the type used, these help to increase faecal water content, increase faecal bulk, or soften stools.

The two most commonly used laxatives in cats are lactulose and polyethylene glycol (aka PEG) 3350. Both are osmotic laxatives - they work by retaining or increasing water within the colon, softening stool and increasing faecal bulk.

PEG-3350

PEG-3350 is better known as Klean Prep or Movicol - yep, the same powder we use for colonoscopy preparation in our patients (or the horrible stuff you have to drink if you’re unfortunate enough ever to need a colonoscopy yourself).

It’s a clear, (usually) flavourless powder that can be mixed with water or food. In severe cases, it can also be given as a CRI via a nasogastric or naso-oesophageal tube in the hospital. 

Important point: PEG can cause minor electrolyte derangements, so keep an eye on these when you use it!

Lactulose

Lactulose is less palatable for our patients than PEG but is an effective method of softening faeces. In humans, it often causes bloating and flatulence as bacteria in the colon ferment it, though we don’t tend to see this so much in our patients.

What about micralax enemas?

Micro-enemas such as micralax contain sodium citrate and work by drawing water into the faeces, which softens it and stimulates the patient to defecate, similar to other osmotic laxatives. They’re an excellent option for constipated patients but not effective for obstipation and megacolon - those patients need a full-blown enema.

And speaking of enemas…

Being able to perform an enema correctly is an important nursing skill. There is more to consider when deobstipating a patient that you might realise - and the procedure isn’t without risk.

It’s also a schedule 3 procedure (yes, I know, one of the less glamorous ones, but if we wanted glamour, we’d all be in a different job, wouldn’t we?!), which means we can - and should - be performing this skill.

So, how do we correctly enema our patient? Here’s what to do:

  • First, make sure your patient is anaesthetised. They can vomit or regurgitate during an enema, so protecting their airway is essential.

  • Use a combination of manual extraction, warm water and water-based lubricant to soften and remove faeces

  • Make sure you don’t add too much water at once, as this can trigger regurgitation or vomiting - instil a maximum of 10ml/kg each time, letting it drain out before re-inserting your catheter or Higginson syringe and instilling more.

What about prokinetics?

Prokinetic medications are the mainstay of supporting colonic motility in our obstipated and megacolon patients. These aren’t a replacement for enemas or laxatives but are a maintenance treatment used once the impacted faecal material has been removed.

Many prokinetics are available, but cisapride is the one used most commonly, as this has been shown to stimulate motility in cats with idiopathic megacolon. It’s an oral liquid given every 12 hours.

Aside from this, it’s all about supportive care.

This will include analgesia, antiemetics, monitoring defecation, maintaining litter tray hygiene and providing nutritional support alongside general nursing care and client education and support, depending on the individual patient.

And what if our patient needs surgery?

Sometimes, our megacolon patients just won’t respond to medical management alone - try as we might with laxatives, prokinetics, the right diet and enemas. 

If your patient isn’t responding to appropriate medical management and is repeatedly getting obstipated, there’s a good chance they’ll need surgery.

This involves removing as much of the colon as possible, except for the volume physically required to perform the anastomosis and maintain intestinal continuity.

These patients can experience weight loss in the first few weeks, so monitoring their weight carefully and ensuring it increases within the following 1-2 months is important. Additionally, they often have faecal incontinence after surgery. They will also have varied changes in their faecal consistency for the first few weeks to months after surgery whilst the remaining GI tract adapts.

While the surgery does come with risks, many patients do very well postoperatively, and clients are usually satisfied with the result and their pet’s quality of life compared to before surgery. Veterinary nurses and technicians are an important source of advice and support during this time, particularly around support with nutrition and managing eliminations - so make sure you’re getting involved in the ongoing care these patients need!

There you have it - the complete guide to managing constipation, obstipation and megacolon as a vet nurse. The most critical areas for us to consider when caring for these patients are nutritional support, maintaining hydration, performing enemas where needed, careful monitoring and supportive +/- postoperative care, and client support - all skills we’re great at!

Did you enjoy this episode? If so, I’d love to hear what you think. Take a screenshot and tag me on Instagram (@vetinternalmedicinenursing) so I can give you a shout-out and share it with a colleague who’d find it helpful!

Thanks for learning with me this week, and I’ll see you next time!


References and Further Reading

Laura Jones
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