Updated: Jul 2, 2020
Calling all feeding therapists: for those of you who are newer to feeding therapy, or maybe primarily work in the picky eating realm (or are a curious parent!) we wanted to take some time to explain what silent aspiration is, how we can diagnose it, and what we can do about it.
Actually, let’s just start with defining aspiration
Let‘s start with the basics: when food or liquid enters the lungs, this is called “tracheal aspiration.” This can occur in a few different ways. (1) The food or liquid can enter the airway and eventually lungs from “above” the airway which means the food or liquid sneaks into the airway as it travels down from the mouth to the pharynx and towards the esophagus, due to disordered swallowing. One or more of the body’s protective mechanisms that usually close the airway during a swallow didn’t work appropriately, and the airway was not protected during swallowing. (2) The food or liquid can enter the airway/lungs from “below” which means the food or liquid is moving from the stomach back towards the mouth and along the way spills into the airway, such as when someone has “acid reflux” or during vomiting—meaning the food/liquid was swallowed appropriately, but came back up and then entered the lungs. (3) The food or liquid enters the breathing tube (larynx/trachea) via an anatomical abnormality that connects the food tube (pharynx/esophagus) with the breathing tube. Similar to #2, the food or liquid is usually swallowed appropriately but then the anatomical issue allows the food or liquid to sneak into the airway.
The literature shows that we all aspirate sometimes (remember when you drank something too fast and coughed, choked, and had to catch your breathe?); even healthy adults aspirate saliva during deep sleep 💤! Our body and lungs are pretty strong and resilient, and kill any bacteria that might sneak into the respiratory tract, but frequent aspiration does a number on the lungs, and can lead to infections, lung damage/disease, and pneumonia.
Silent aspiration- what does that mean
So what do we mean when we say “silent aspiration”? When a swallowing therapist evaluates a patient, they look for overt signs and symptoms of swallowing dysfunction. These red flags include coughing, watery eyes, congestion during feeding, sputtering, changes in breathing patterns, and color changes. But sometimes, swallow dysfunction occurs WITHOUT any of these overt signs, and the therapist has to make an inference that something is going wrong OR the aspiration is seen on a test, such as a Modified Barium Swallow Study (MBSS) but the patient didn’t show any overt or outward signs during the clinical feeding evaluation or during the MBSS.
If aspiration occurs without overt, observable symptoms, this is called “silent” aspiration.
There are many research articles that look at different elements of silent aspiration but there are actually relatively few that define it and clarify which signs are considered “overt” vs “subtle.“ There are a few that do describe and define silent aspiration as we define it above but based on those it isn’t clear if certain signs (such as a desaturation registered on a cardiopulmonary monitor) would qualify as overt signs of aspiration or if a patient who aspirated and didn’t cough or show any other outward signs but whose heart rate spiked or who had a light stridor would still be considered to have “silent aspiration” if aspiration was confirmed, despite the presence of those subtle but observable signs.
Prevalence & risk factors
When it comes to the prevalence of silent aspiration there are different numbers depending on what study you read but there was a 2018 study by Velayutham et al which found that out of almost 1,300 children under 18 referred for MBSS (due to feeding difficulties) 34% aspirated and out of those patients who aspirated, 89% aspirated silently. A 2011 study by Weir et al which reviewed data on 300 children who were seen for MBSS found that 34% (oddly same as the other study) aspirated and out of those who aspirated, 81% aspirated silently.
The 2011 study by Weir et al found that those most likely to aspirate silently we’re children with neurologic impairment, Cerebral Palsy, lung disease, or those who receive tube feeds.
Identifying silent aspiration
As we noted above there are some subtle signs that can clue a therapist in that this patient may be aspirating even if they aren’t coughing or showing signs of distress. These signs observed while a patient is eating include:
light and intermittent congestion
small dips in oxygen saturation
increases in respiratory rate (tachypnea)
In infants we sometimes see a pattern of suck/spit (where the breast milk or formula appears to be spit out of the corners of the mouth- not just spilling down the chin or from the corners of the mouth) which may be a subtle sign of aspiration.
Here is a video of a little guy showing some subtle respiratory changes while breastfeeding. (You’ll need sound for this.)
These would be considered “subtle“ signs of aspiration and wouldn’t exactly be a cause for immediate concern. But if these signs were occurring consistently AND the child had other risk factors (see below) it may be worth looking into this more—probably by first modifying the positioning and pacing and doing more observation, then possibly referring for an instrumental evaluation of swallowing, such as a Fiberoptic Endoscopic Evaluation of Swallow (FEES).
Sometimes, we can identify one or more signs that are even less obvious than a desaturation or a bradycardia episode, that may suggest silent aspiration—poor weight gain, frequent fevers for no specific reason, frequent mild respiratory infections, some breathing problems... and even food refusal! Especially when it comes to bottle-fed infants, we have found a connection between silent aspiration and bottle refusal in our own clinical practices.
“The body will always prioritize breathing”
The body will always prioritize breathing, and if an infant’s breathing is compromised, they may shut down and fall asleep instead of feeding or gag, turn away, and refuse the bottle. Research suggests that MOST aspiration in infants IS silent, so a trained clinical eye and possibly an instrumental evaluation is an important part of the diagnostic process.
We don’t mean to make you nervous, or to make you assume that every patient who is a picky eater or refuses a bottle is silently aspirating. We simply want you to consider a swallowing problem as a part of your clinical feeding evaluation if there aren’t any other explanations to explore AND especially if there are at least one other “soft” sign of silent aspiration, such as:
poor weight gain
consistent low grade fevers
any of the specific medical or developmental issues listed above
If you are concerned about silent aspiration you will most likely want to speak with the medical team about referring your patient for an instrumental evaluation of swallowing, such as an MBSS, which can help guide your clinical intervention plan. You may need to use techniques to increase your patient’s swallow safety, such as pacing or modifying the texture of the patient’s food or liquids. If you’re not sure how to evaluate or make a clinical plan, make sure to talk to the physician about a referral to a specially trained OT/SLP to make sure your patient is safe! If you want to learn more on this topic and feel more confident about your intervention plans, consider taking our continuing education course: The Neurobiology of Swallowing & Dysphagia!