Through Thick or Thin: To cough or not to cough…That is the silent question

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Title: Cough response to aspiration in thin and thick fluids during FEES in hospitalized inpatients
Authors: Miles, McFarlane, Scott, & Hunting
Journal: International Journal Of Language & Communication Disorders
Year of Publication: 2018
Design Type: prospective observational study
Purpose: “The aim of this prospective observational study was to report aspiration prevalence and cough response to aspiration across two fluid viscosities and two measured volumes in patients referred for FEES in an acute hospital setting.”
Population: adult inpatients across 2 hospital settings

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Resident Susie is coughing at the table😳

The nurse saw patient John Doe cough when drinking water with his pills😦

Home health Harry’s spouse says he sometimes coughs when he drinks😲

Outpatient Oscar is here because he “didn’t cough with thickened liquids” in the hospital, but he can’t stand them and is determined to “get off that stuff”😬

🚨Are your alarm bell sirens loudly ringing in your head just reading these statements?🚨

Well my SLP friends, luckily there is research that can help dampen those bells and let us breathe a bit instead of entering automatic panic mode!

In case you haven’t heard yet, this one is A KEEPER. One to be stashed, referenced, quoted, discussed, shared, and the one that likely changed the game by changing LOTS of clinical practices when it comes to testing and recommending thickened liquids at the bedside.

Before getting into the thick of it (pun very much intended😉), I may be either easy to please or the idea of right off the bat showing a short “What this paper adds” box and how clinically relevant the findings are is a beyond brilliant idea! So even if you only have a quick second, you can at least get the gist of the (honestly already relatively short) article! Can we all just collectively agree that this is what every paper needs?!???👏👏👏👏Angelsintheoutfield Itsabouttime GIF - Angelsintheoutfield Itsabouttime Abouttime GIFs

I surprisingly learned that the use of thickened liquids isn’t native to just the U.S., but internationally is the “most common used dysphagia management strategy😲! Even though the ‘thickened liquid debate’ has been going on at least since I graduated as a wee lil SLP, the authors still give a brief review and history about how this modification even came about:

“The principle underlying the use of thick fluids is that increased viscosity reduces the speed of the bolus and that this may reduce aspiration in some patients (Logemann et al. 2008; Clave et al. 2006).”

“The typical clinical scenario is that a patient is observed to cough on thin fluids, subsequently trialled on thicker fluids, and the absence of a cough is assumed to indicate the resolution of aspiration. However, pilot research in our laboratory has called into question this basic assumption.” p.1

Seriously, even the Introduction is enough to blow your mind🤯, open your eyes😳, and question your previously held thoughts🤔–especially after finding out that“silent aspiration holds a 13-fold risk of aspiration pneumonia compared with no aspirationº, recommending thick fluids for patients who silently aspirate this consistency is concerning,” along with the fact that the increased viscosityº can actually increase a patient’s risk of developing a pulmonary infection if aspirated simply because it’s not pure clear water (ya know, the thing our body is made up 60% of). I for one will definitely be adding the references from those quotes to my already-never-ending-long list of things to read up on🤓.

The authors’ predictions (aka hypotheses) seem pretty close to what some of us are probably thinking at bedside or even with instrumentals:

  1. Thin liquids are gonna be more likely aspirated than thickened liquids
  2. When aspiration occurs, a cough response won’t be consistent within the same consistency/amount even across multiple trials 
  3. Larger amounts of liquids will elicit a cough response (versus smaller amounts)
  4. When aspiration occurs, a cough response won’t be consistent for thin or thick liquids

Have you found yourself saying or asking any of those in your mind while assessing a patient?? 🙋‍♀️🙋‍♀️

Mine might usually go something like:

‘Hm, they coughed when I gave them a larger sip…I wonder if that will happen again with another?🤔

‘Hm, they coughed for larger amounts only…I wonder if that might actually be a beneficial protective reflex of the airway or not?🧐

Or just… ‘Hmm…?🤨

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This particular article really is a diamond in the rough because it is actually set in (2 urban) acute/inpatient hospital environments, something that is not always easy to find (I hear you acute care SLPs😉😉)! The etiology also closely mimicked what we inpatient SLPs might typically see as well:

  • 28% stroke
  • 18% other neurological conditions (i.e. TBI, progressive neurological disorders)
  • 28% cardiovascular critical care
  • 13% respiratory condition
  • 5% spinal injury
  • 7% other

Additionally, to be eligible for a subsequent standardized FEES, all 180 participants had a prerequisite that we are all too familiar with: “inconclusive bedside clinical swallowing evaluation,” (i.e. their criteria meant “wet voice or coughing on oral trials”). Or something many of us, unfortunately, are less likely to have at our fingertips: failing a cough reflex test.

Curious what their ‘standardized’ FEES exam looked like? Well lucky for you the authors included the specific details to help with replication!🤩🥳

  • 30 seconds at rest for observation
  • 3 (5 ml) tsp IDDSI level 0 liquid
  • 3 (50 ml) cup IDDSI level 0 liquid
  • 3 (5 ml) tsp IDDSI level 2 (mildly thick) liquid
  • 3 (50 ml) cup IDDSI level 2 (mildly thick) liquid
    • all tsp trials presented by SLT
    • all cup trials were given to patient with instructions “drink until it is all gone” (hand-over-hand support was given as necessary)

Don’t worry, just as you or I would do, given the acuity of the patient populations, they still ended or shortened their FEES protocol if needed for overall safety (videos were excluded if this happened before both thin/thick liquids were trialed though). And for all you FEES-ers out there, they only used a water lubricant and no topical anesthesia, along with blue dye for visualization. As far as all the other specifics in scopes and equipment– sorry guys you’re just gonna have to check the full article out because I’m definitely still just in the bare basics when it comes to those details🙃.

A final note and cause for some 👏applause👏, the authors tried to control the temperature for all fluids, giving them straight from the fridge, and also created their own randomization sheet in order to control for any order effectº. Thats My Job GIFs | Tenor

While the raters who reviewed the videos afterward were blinded to the patient demographic data and etiology, they (obviously) were unable to be blinded by what consistency or amount was being tested (to be fair, it is kind of our job to know the difference between consistencies and amounts😅😜).

As far as the measures that were used, look no further than the validated Pen-Asp Scale, which was “rated immediately after the final spontaneous clearing swallow and/or cough response.” Afterward, half of the FEES videos were randomly reviewed and rated by another author completely blinded even to the study’s purpose, thereby improving inter-rater reliabilityº and reducing bias. (FYI: All FEES raters had >5 years experience interpreting FEES😎)

The authors also took it a tiny step forward from the Pen-Asp Scale by focusing exclusively on cough response to aspiration and creating a ‘non-traditional categorization of aspiration events,’ which highlights the contact (or lack of) at the vocal folds, and what happens next (cough response? effectiveness?) and are keenly aware of the capabilities and limitations when it comes to this event on FEES, which also served as a quick ‘n dirty cranial nerve review😉:

“Although intact sensation of the vocal folds and the subglottic space requires afferent information from different sensory nerves, namely the internal branch of the superior laryngeal nerve (iSLN) and recurrent laryngeal nerve (RLN) respectively, a lack of response to foreign material either on or below the vocal folds would be considered clinically relevant and therefore this study did not differentiate between the two.” p.3

There’s lots more info that’s shared too as far as who had trachs, length of stays, discharges, and more, so be sure to check out the article yourself!!🤓

Ok, before moving straight into what was found and because I’m trying to learn more about the non-fun aspects when it comes to research (so I can share and help others like you understand more🤓🙂!), here’s a quick lil-diddy as they say, for a way to know just what the heck they’re talking about with statistical tests. The article actually gives a sentence for explanation just what each test actually looks at (which can be rare), so here’s a glimpse:

*originally created*

And no, I won’t spend my night crying if you quickly scroll over this part faster than a targeted ad, nor if you have anything to add! So feel free to do whatever you need😉.

Talking through the Thick of it…

Of the 252 FEES videos (initial/repeat) that were able to be analyzed:

  • 32% (81 total) had an instance of aspiration (PAS>5) for thin
  • 18% (45 total) had an instance of aspiration for thick liquids
  • 9 FEES showed an instance of aspiration for thick but not liquids
  • For teaspoon thin liquids: 91% improved on repeat FEES

If you’re sitting there on the edge of your seat wondering furiously if viscosity or volume has any influence on PAS scores:

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There was a significant association between PAS scores and viscosity and volume, with higher PAS scores for thin liquids at 5 ml and 50 ml trials compared to thick liquids, (higher volumes for thick liquids was not significant).“If a participant aspirated on a single consistency, this was four times more likely to occur with a thin fluid trial than thick fluid trial,” just don’t get me started when it comes to that and the development of pneumonia though😜🙅‍♀️.

However. . . . .

When aspiration occurred, it was SILENT in:

  • 56% (5 ml thin)
  • 65% (50 ml thin)
  • 72% (5 ml thick)
  • 67% (50 ml thick)

I think those increasing numbers speak for themself as you read down the increasingly viscosities . . . And it also closely mimics previous findings as well:

“In patients who aspirated, silent aspiration rates are higher than rates of aspiration with a cough response across all viscosities and volumes. This finding again reflects the critical care setting where high silent aspiration rates are well established (Hafner et al. 2008, Leder et al. 1998), and may also be influenced by recruitment criterion, where many participants were referred for FEES following failed cough reflex testing.” p.7

In case the underlined above finding was too subtle, this study found a brand spanking new finding that thicker≠better, and now we have something to educate our fellow colleagues with:

Another speed bump | The Cancer Chronicles
*internal freakout*

“One finding that is novel to published research was a cohort of mixed ages and aetiology participants (4%) who were observed to aspirate thick fluids in the absence of thin fluid aspiration. This has important implications for clinical practice and debunks the idea that thick fluids are universally safer than thin fluids.” p.7

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There was a significant association between airway responsiveness and viscosity, with a higher proportion of aspiration being silent in thick than thin fluids. If a patient aspirated a teaspoon of thick fluids, in two-thirds of cases, it was silent.” p.8

If you read further, the authors really go deeper with their due diligence in trying to hypothesize and figure out more about this phenomenon by explaining how summationº could possibly be the rationale behind it, supposing that larger or heavier volumes could generate more of an irritant for the cough response, and smaller amount/lighter (thin) liquids are unable to “induce greater pressure or remain on vocal folds for longer.”

But unfortunately, that doesn’t match with what the authors found (that’s science guys😉), and again, also mirrors the whole ‘volume-dependent’ evidence for silent aspiration from Leder et. al (2010) and also might lead you to wonder more about this topic (e.g. Yale Swallow Protocol):

“However, this was not supported by our data, with aspiration of thin fluids more likely to elicit a reflexive cough than thick fluids. It is possible that fast moving thin substances penetrate deeper and trigger a subglottic cough response. These findings may also reflect a volume-dependent threshold for cough. Specifically, aspiration of a larger volume or proportion of the bolus with thinner viscosities would lead to greater stimulation and therefore a higher chance of coughing.” p.8

Take a couple moments to get your jaw off the floor, allow your eyes to settle from rolling, and reformulate your mind after that explosive bomb of info because the article has even more to absorb (if you still can🥴🤯).

PAS within same consistency/amount across 3 trials:

“There was no significant difference in PAS scores within the three 5 ml trials of thin fluid, three 5 ml trials of thick fluid, three 50 ml trials of thin fluid or three 50 ml trials of thick fluid.” p.5

So, if they tested something 3 times, nothing jumped out of significance and really varied across those 3 attempts.

“As has been previously reported (Molfenter and Steele 2014), aspiration was not a consistent phenomenon across repeated swallows in this cohort. Although, while variation was evident across trials of the same bolus viscosity and volume, there was no statistically significant difference in PAS scores across the three trials. Sampling more than one repetition of a bolus type is clinically wise.” p.7

And if you were thinking that the diagnosis/etiology had anything to do with the results. . .

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“There was no significant difference in incidence of aspiration, aspiration with cough and silent aspiration for thin or thick fluids during a patient’s first FEES across aetiologies” p.5

Personally, I have to say I always find this pretty remarkable since we can see such a wide variety of diagnoses in a day, especially those with higher risk for silent aspiration in this setting!🤯

Overall, there was a lot of variability even within one person, which is why the article further shows evidence regarding:

  • “Although thick fluids may reduce aspiration in some patients, their use as a panacea for all aspiration events is not supported by this study”
  • “Sampling more than one repetition of a bolus type is clinically wise”
  • “Use of protocols that assess larger volumes of fluids to push patients and probe the swallow, and caution the use of small boli as a compensatory strategy without instrumental assessment validation”

And hopefully, it goes without saying, that everything is to be dependent on each individual patient case, along with each clinician and facility’s capabilities.😉

At the end of the day (or before work tomorrow)

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Well, despite some unavoidable limitations like selection biasº, exclusion of possibly critically medically fragile patients (so, we can’t generalize all this to these patients!), and the realization that the Pen-Asp Scale still isn’t always the end-all-be-all when it comes to airway sensory integrity, the study really shows us a LOT (if you don’t believe me, go back and reread the review or the full article yourself!!🤓😀

But how can I go on knowing all the wrongs I’ve done?!?😱😓🤦‍♀️🙇‍♀️

I am right there with you and can remember like it was yesterday, back when I was taught how to do a clinical bedside swallow evaluation, and thinking to myself, “Oh, you just give them something, and whatever they don’t cough on that’s what you recommend.” 🤦‍♀️😓🤦‍♀️😔🤦‍♀️

While I’m not advocating Scarlet letters be given out and each one of us admitting to a “guilty” thickened liquid mugshot (although maybe we should be forced to do the Thickened Liquid Challenge😅?), nor will I tell each and every clinician what to do (unless maybe if it’s my student or CF). I’ll leave that up to the experts because the evidence is there (whether we want to believe it or not), and each one of us carries our own responsibility of working at the top of our license and using our own clinical judgment where we work.

But being aware leads to acknowledgment. Acknowledgment can lead to reflection. And reflection can further lead to avoiding cognitive dissonanceº and ultimately improve critical thinking, which can then help with change.🙂

So, all SLPs reading this:

Go forth. Read. Learn. Grow. Change.

And be a better SLP than you were yesterday.



How can you use this article?!?

Well hopefully, it is pretty apparent to us now…

But maybe you’re a new CF being pressured into making critical decisions at bedside when you might know better or don’t have enough needed information for a recommendation?

Maybe you’ve been making many recommendations for a long time, despite patients/caregivers declining these modifications or strategies and are wondering how to move forward??

Either way, because we work in a clinical world (and I am a clinical girl😉), the authors are able to recognize but also push us out of our comfortably thick zones, leaving the rest up to us:

“In a clinical context, coughing on one trial and not on another trial is often interpreted as the elimination of aspiration. The findings from this study, considered in the context of a lack of existing research demonstrating the benefit of thick fluids for reducing poor outcomes such as pneumonia (Robbins et al. 2008), highlight the need for thick fluids only to be considered in cases where they are shown by reliable assessment such as FEES or videofluoroscopy to eliminate aspiration.” p.9


  • “This large mixed-aetiology cohort is representative of the acute care setting, with the wide age range reflective of the heterogeneous nature of acute hospital care.”
  • “In some patients aspiration does not consistently trigger a protective cough response, and responsiveness may vary across different fluid viscosities as well as volumes. In two-thirds of patients who aspirated a thick fluid bolus this occurred silently.”
  • “Discrepancies in cough response across bolus types spanned both early (first FEES) and later admissions (repeat FEES) and were dispersed across patients rather than seen as a trait of some individuals. This perhaps adds strength to the argument that cough response variability is not a symptom of severe impairment rather a threshold-dependent response based on amount of aspiration that reaches sensory receptors at any point in time.”
  • “The finding of inconsistent cough response to aspiration across both different fluid volumes and viscosities raises critical concerns about the validity of assumptions made during bedside swallow evaluation. Patients cannot simply be categorized as ‘overt’ or ‘silent’ aspirators, and instrumental swallowing assessments are strongly encouraged to guide treatment”

Article Referenced:

Miles, A., McFarlane, M., Scott, S., & Hunting, A. (2018). Cough response to aspiration in thin and thick fluids during FEES in hospitalized inpatients. International Journal Of Language & Communication Disorders53(5), 909-918. doi: 10.1111/1460-6984.12401

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