Research Watch Report: Systematic Reviews of Dysphagia Assessment and Intervention in Adults

Dysphagia is one of the most commonly encountered disorders among speech-language pathologists (SLPs) whose clinical practice focuses primarily on adults. Bhattacharyya (2014) estimates that, although only a minority of these cases are reported, 1 in 25 adults experiences dysphagia on an annual basis. SLPs are uniquely qualified to evaluate and treat this disorder, as we have extensive knowledge and skills related to the upper airway and digestive tract (ASHA, n.d.). In addition, many of our clients across the lifespan present with dysphagia as a sequela of their primary diagnoses, particularly adults with organic and/or neurogenic etiologies. Dysphagia can range in severity, with milder cases creating aggravation or annoyance for our clients, while more serious cases put our clients at significant risk for a host of grave illnesses, including dehydration, malnutrition, and aspiration pneumonia. In addition to its obvious physiological effects, the presence of dysphagia, regardless of severity, may contribute to considerably diminished quality of life. 

Dysphagia is a widespread and potentially life-threatening disorder. As SLPs, we must utilize the most effective assessment and treatment techniques. One of the best ways for busy clinicians to stay abreast of current research is by accessing systematic reviews and meta-analyses. Systematic reviews “involve a detailed and comprehensive plan and search strategy derived a priori, with the goal of reducing bias by identifying, appraising, and synthesizing all relevant studies on a particular topic” (p. 57, Uman, 2011). In other words, researchers develop a clinical question (e.g., Population - Intervention - Comparison - Outcome or PICO), then do an extensive search of available and relevant literature. Once the researchers identify the independent studies that are most appropriate for their clinical question, they summarize and synthesize the results of those studies to determine an answer to their question.

Systematic reviews may include meta-analyses. Meta-analysis is “a statistical technique for combining the findings from independent studies” (Crombie & Davies, 2009, p. 1). Meta-analyses go a step further than systematic reviews in that their purpose is to aggregate data from a number of relevant studies and include many participants to determine the treatment effects of a given intervention. The meta-analysis (of randomized controlled trials) is considered the highest level, or most rigorous type of research design, of the evidence hierarchy (see https://www.asha.org/research/ebp/assessing-the-evidence/).

Systematic reviews and meta-analyses are important for healthcare providers and provide a foundation for the development of guidelines to inform clinical practice (Moher et al., 2009). Indeed, ASHA’s National Center for Evidence-Based Practice in Communication Disorders (N-CEP) has developed a number of systematic reviews of various clinical populations to serve as a basis for clinical guidelines (see https://www.asha.org/Research/EBP/EBSRs/). 

This research brief summarizes several systematic reviews/meta-analyses of dysphagia assessment and intervention. All of studies reviewed here indicate that they followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement (Moher et al., 2009). PRISMA includes a checklist of 27 items that should be addressed in systematic reviews and meta-analyses in order to help ensure the quality of such studies. Maintaining a high level of quality is important because of the potential for systematic reviews and meta-analyses to influence clinical guidelines and practice patterns across a variety of disciplines. However, just because an article does not specifically state that it followed the PRISMA statement does not automatically mean that the study is not of high quality. The studies summarized here were selected for their overall quality as well as their relevance to SLPs working with adults with dysphagia.

Article 1: Britton, D., Roeske, A., Ennis, S., Benditt, J., Quinn, C., & Graville, D. (2018). Utility of pulse oximetry to detect aspiration: An evidence-based systematic review. Dysphagia, 33, 282-292.

Background: What was the rationale and/or clinical question guiding this study? Pulse oximetry is a non-invasive technique used to measure the amount of oxygen (oxygen saturation) in a patient’s blood. Some healthcare providers consider it a tool that can be used to determine if patient is aspirating. The authors of this article explain that the rationale for this particular application of pulse oximetry is that aspiration may lead to a change in the way or amount of oxygen taken into the airway, thereby causing the oxygen levels in the blood to drop. However, the evidence for the use of pulse oximetry to determine the presence of aspiration is mixed. The clinical question guiding this study was: In patients with dysphagia, does a decrease in oxygen saturation (as measured by pulse oximetry) appear to indicate aspiration during swallowing?

Method: How were the studies selected? The authors searched available literature for peer-reviewed studies that used pulse oximetry to detect aspiration while confirming the presence of aspiration via instrumental evaluation with modified barium swallow study (MBSS) or fiberoptic endoscopic evaluation of swallowing (FEES). They initially identified 294 studies, but after applying exclusion criteria, 10 studies were included in the systematic review. Studies were excluded for several reasons, such as they were written in a language other than English, included children as participants, or used a non-instrumental clinical swallowing examination. In addition, only peer-reviewed journal articles were included; conference or committee reports were excluded from consideration.

Results and Clinical Application: What does the synthesis of results suggest about the answer to the clinical question? In their review and synthesis of the 10 included studies, the authors found that most of them focused on the stroke population. All of them examined oxygen saturation levels while conducting an instrumental swallowing evaluation to confirm the presence of aspiration. Four studies included a control or comparison group; the other six did not. All of the studies were characterized as being at a low to moderate level of evidence (equivalent to Level IIB or III on a widely used evidence rating hierarchy in our discipline; see https://www.asha.org/research/ebp/assessing-the-evidence/). Some of the issues that rendered the ten studies at the low to moderate level of evidence were differing values used to define a drop in oxygen saturation levels, inclusion of mixed populations, lack of control or comparison group, lack of control for texture or viscosity of tested consistencies, and varying definitions of what classified a participant as an aspirator.

The authors of this systematic review stated that the findings from the ten studies they analyzed were “mixed and highly variable” (p. 286). They found wide ranges reported for sensitivity of pulse oximetry in the detection of aspiration among the studies (10-87%) and for specificity (39-100%). Of the four studies that used a control or comparison group design, three reported “a lack of change or relationship between aspiration and oxygen desaturation” (p. 286). In light of these findings, the authors of this systematic review determined that the evidence does not support the use of pulse oximetry to detect aspiration. 

Article 2: Wang, B., Carter, F., & Altman, K. (2018). Relationship between dysarthria and oral-oropharyngeal dysphagia: The current evidence. Ear, Nose, & Throat Journal, 97, E1-E9.

Background: What was the rationale and/or clinical question guiding this study? Pointing to the oral motor control and coordination deficits that are common to both dysarthria and dysphagia, the authors suggest that the presence of dysarthria in a patient is a strong indicator for the presence of dysphagia. A challenging aspect to the study of the relationship between these two disorders is the varying ways in which they are measured in the literature as well as the different clinical presentations of the six dysarthria subtypes (i.e., hypokinetic, hyperkinetic, flaccid, spastic, ataxic, and mixed). The clinical question guiding this systematic review was: Can a measure of dysarthria be used to screen patients for dysphagia?

Method: How were the studies selected?  The authors searched available literature for relevant studies. They initially identified 1060 studies. Articles were excluded if they were published in a language other than English and if they were published before June 1995. After screening these articles for exclusion and inclusion criteria, the authors were left with 24 articles for review. These 24 articles were comprised of three categories: (1) 12 articles whose participants had neuromotor/ neurodegenerative diseases; (2) 11 articles whose participants had cerebrovascular diseases; and (3) one article that included participants of both the neuromotor/neurodegenerative disease and cerebrovascular disease populations. The neuromotor/neurodegenerative diseases represented included amyotrophic lateral sclerosis (ALS), Parkinson disease, myasthenia gravis, and multiple sclerosis, among others. The cerebrovascular diseases represented included cerebrovascular accident (CVA), traumatic brain injury (TBI), cerebral palsy, and vascular dementia. Given the differences between these two distinct categories of populations, the authors decided to examine the two categories separately.

Results and Clinical Application: What does the synthesis of results suggest about the answer to the clinical question? The authors of this systematic review noted the variability among the selected studies, including different types of measures of dysarthria and dysphagia (i.e., objective, observed, self-reported). They mention the potential limitations of subjective measures and self-reporting, in particular, as patients might be likely to under-report dysphagia symptoms due to fear that a doctor will recommend an alternative means of nutrition and hydration (i.e., PEG tube) or because the patient simply does not realize their symptoms as being consistent with impaired deglutition. The evidence reviewed “included cross-sectional observational studies that did not contain level 1 or 2 prospective evidence” (p. E7). In other words, the 24 articles selected for this review would be characterized as being at a low to moderate level of evidence.

With regard to their clinical question, the authors state that, despite the limitations of the available relevant evidence, “dysarthria is a strong clinical clue to the presence of dysphagia in neuromuscular diseases” (p. E8). Further, they highlight the need for longitudinal studies of the relationships between dysarthria and dysphagia based on findings in their review they refer to as “hints that dysarthria might precede the development of dysphagia and that their severity is correlated with each other” (p. E8). Note: The relationship between the presence of dysarthria has previously been identified as an indicator of moderate to severe dysphagia (see Daniels et al., 1997).

Article 3: Kaneoka, A., Pisegna, J., Saito, H., Lo, M., Felling, K., Haga, N., LaValley, M., & Langmore, S. (2017). A systematic review and meta-analysis of pneumonia associated with thin liquid vs. thickened liquid intake in patients who aspirate. Clinical Rehabilitation, 31, 1116-1125.

Background: What was the rationale and/or clinical question guiding this study? The authors of this study cite the high risk of pneumonia associated with aspiration, as well as the increased treatment costs and mortality rates resulting from the illness. They also point to evidence that thin liquids, which require a timely and coordinated swallow response in order to swallow them safely, lead to more frequent instances of aspiration than do thickened liquids. Further, while research suggests that thickening liquids as an intervention strategy can eliminate aspiration immediately, we don’t have evidence that thickening liquids is an effective strategy over the long-term. In fact, recommending the restriction of thin liquids beyond short-term timeframes might lead to decreased patient/family compliance, and result in dehydration, another potentially serious complication among chronically ill or elderly patients. The clinical question guiding this study was: Among patients who are known to consistently aspirate thin liquids, are pneumonia risks increased for those who drink thin liquids using safe swallowing strategies compared to those who drink only thickened liquids?

Method: How were the studies selected? The authors performed a comprehensive search of the literature relative to their guiding question. They included studies that were published or unpublished randomized controlled trials or prospective studies that were not randomized controlled trials, indicating that the studies reviewed and analyzed here would be considered high-quality evidence, equivalent to Level IB or IIA on a widely used evidence rating hierarchy in our discipline; see https://www.asha.org/research/ebp/assessing-the-evidence/). Furthermore, they reviewed only studies of adults with dysphagia that compared the use of thin liquids with safe swallowing strategies to the use of thickened liquids, and reported rates of pneumonia among the participants. They excluded studies that did not use instrumental swallowing evaluation to confirm aspiration of thin liquids. No other exclusions were applied.

A total of 2465 sources were identified initially. After screening, the authors found that seven studies met all inclusion criteria. All seven studies were randomized controlled trials (Level IB evidence). Five of these were published journal articles, while the other two were presented at professional conferences. The systematic review of the seven studies revealed that participants included outpatients and inpatient across several settings, including subacute, acute, rehabilitation hospitals. Clinical populations represented were individuals with Parkinson’s disease, dementia, acute stroke, and acute brain injury. The seven selected studies included a total of 650 participants.   

One study was a large randomized controlled trial that included multiple facilities. The experimental protocol for that project included random assignment of participants to different experimental conditions to examine possible group differences (thin liquids with chin-down position vs. nectar-thick liquids without chin-down position vs. honey-thick liquids without chin-down position). This study included a longitudinal component, as participants were monitored for three months, and the compliance of caregivers and staff members was also tracked during that time.

The other six studies were similar to one another in methodology, generally comparing pneumonia outcomes for patients who were allowed thin water protocols vs. control group patients who were restricted to thickened liquids only. These thin water protocols allowed free (thin) water between meals, with restriction to thickened liquids with meals. The authors of this study note that the free water protocols among these six studies were not necessarily equivalent. For example, some of the free water protocols implemented required rigorous oral care prior to patients’ intake of water, while others did not. Additionally, some studies included recommended compensatory strategies based on instrumental evaluation, while others did not. Family and/or staff compliance was not monitored in these six studies. 

The authors of this systematic review completed a meta-analysis on the six studies that were comparable to one another, excluding the large multi-site randomized controlled trial due to its different research design and protocol. Data from 135 participants was included in the meta-analysis. These participants did not have any conditions associated with risk factors for pneumonia, such as low cognitive function, pre-existing respiratory conditions, gastroesophageal reflux disease, nasogastric tube placement, and tracheostomy. Despite the common co-occurrence of these conditions with dysphagia, the authors of the six studies excluded participants who reported having any of them.

Results and Clinical Application: What does the synthesis of results suggest about the answer to the clinical question? A statistical analysis of the 135 participants in the six selected studies did not reveal a significant difference in pneumonia outcomes for patients following a thin water protocol as compared to those who were restricted to thickened liquids. In addition, analysis of the potential risk of bias for the five published studies was rated as high. Bias occurs when an external variable influences the results of research. For example, four of the five studies assessed for risk-of-bias were deemed to be at risk for detection bias. Detection bias refers to differences in the ways that the individuals who are assessing outcomes define or measure those outcomes. Bias is considered to be a confound in research, and may render results unreliable, as it can lead to over- or under-estimation of the outcomes.

Despite the limitations of the studies analyzed here, the authors suggest that these findings could still inform clinical practice in the dysphagia population. Given the lack of a clear relationship between thin liquids and the development of pneumonia in the participants of these studies, clinicians might consider a more liberal use of free water protocols, particularly among patients who have a low risk of pneumonia (i.e., those who do not present with risk factors for pneumonia, such as low cognitive function, pre-existing respiratory conditions, gastroesophageal reflux disease, nasogastric tube placement, and tracheostomy).

Article 4: Schwarz, M., Ward, E., Ross, J., & Semciw, A. (2018). Impact of thermo-tactile stimulation on the speed and efficiency of swallowing: A systematic review. International Journal of Language and Communication Disorders, 53, 675-688.

Background: What was the rationale and/or clinical question guiding this study? Thermo-tactile stimulation (TTS) is a technique in which the clinician repeatedly and firmly strokes the faucial arches with a cold swab or small laryngeal mirror to improve or trigger the swallow reflex in individuals presenting with swallow delays. The hypothesis informing the procedure suggests that the swallow reflex may be modified or initiated by stimulating areas of the oral cavity innervated by the superior laryngeal and/or glossopharyngeal nerves. Despite a lack of research supporting TTS, SLPs around the world report using it as both an intervention and compensatory strategy for patients with delayed swallows. The clinical question guiding this review was: What is the effect of using TTS as an intervention or compensatory strategy with individuals with delayed swallows?

Method: How were the studies selected? The authors searched all available literature regarding the use of TTS on swallowing from the earliest date possible to September 2017 and initially identified 599 articles. They narrowed their review to 10 articles by excluding those written in a language other than English as well as those that discussed any dysphagia therapy technique other than TTS. Only studies involving adult participants were included in the final systematic review. The authors stated that they intentionally avoided applying additional exclusion criteria to their search in an effort to provide a more complete examination of any potential beneficial or harmful effects of TTS implementation.

A modified Downs and Black rating scale (Downs & Black, 1998) was utilized to assess the quality of the evidence that was to be reviewed. This scale evaluated all of the articles reviewed based on 15 criteria related to study design and reporting. Some of the criteria included clarity of the hypothesis, descriptions of participant recruitment and characteristics, evidence of compliance with the intervention, use of a control group, and use of appropriate statistical tests. The authors determined that “high quality” would be defined as meeting more than 60% of the modified Downs and Black criteria. Of the ten articles included for review, two articles met criteria for high quality, while eight did not.

Results and Clinical Application: What does the synthesis of results suggest about the answer to the clinical question? All of the subjects in this review were adults with oropharyngeal dysphagia resulting from a neurological event, such as a stroke or TBI, or a neurogenerative disease. Four of the 10 studies investigated patients’ changes in swallow speed and function immediately following TTS. The remaining six studies evaluated the efficacy of TTS as a rehabilitative intervention to improve swallow speed and function over a period of several days or weeks. All of the experiments used videofluoroscopic swallowing studies (VFSS) to evaluate outcomes.

When used as a compensatory strategy immediately before a swallow, TTS was shown to significantly improve the timeliness of the swallow reflex; however, very small and statistically insignificant changes in swallow function were observed in participants who received TTS as a rehabilitative intervention over a period of several days or weeks. Additionally, the authors note that, despite documenting immediate improvements in speed of swallow trigger, no studies have yet indicated that TTS reduces rates of penetration or aspiration over time.

Although some positive effects of TTS have been documented, the authors note that inconsistent methodology among studies complicated their ability to offer conclusive statements regarding the efficacy of the intervention. As noted above, they judged 7 of the 10 articles included in their review to be of low to moderate quality based on the modified Downs and Black scale. As a result, they concluded that there is low-level evidence to suggest the use of TTS as a compensatory strategy immediately before a swallow. Therefore, the authors encourage clinicians to consider the use of TTS on a case-by-case basis rather than as a comprehensive intervention in dysphagia treatment. 

Final Thoughts

These four systematic reviews (including one meta-analysis) represent some of the most current findings in the area of dysphagia in adults. As SLPs, we can incorporate this scientific evidence into our practices to guide clinical decision making, along with the other components of evidence-based practice, clinical expertise and client preferences. However, one of the key conclusions of these articles is that, although there seem to be numerous studies of dysphagia in adults, much of the available evidence is of low to moderate quality. Although there are challenges associated with conducting dysphagia research, our field needs more high-quality studies so that we can continue to help improve swallowing function in our clients.