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  1. Garon, Bernard R.
  2. Sierzant, Tess
  3. Ormiston, Charles


The purpose of this retrospective study of aspiration and the lack of a protective cough reflex at the vocal folds (silent aspiration) was to increase the awareness of nursing staffs of the diagnostic pathology groups associated with silent aspiration. Of the 2,000 patients evaluated in this study, 51% aspirated on the video fluoroscopic evaluation. Of the patients who aspirated, 55% had no protective cough reflex (silent aspiration). The diagnostic pathology groups with the highest rates of silent aspiration were brain cancer, brainstem stroke, head-neck cancer, pneumonia, dementia/Alzheimer, chronic obstructive lung disease, seizures, myocardial infarcts, neurodegenerative pathologies, right hemisphere stroke, closed head injury, and left hemisphere stroke. It is of high concern that the diagnostic groups identified in this research as having the highest risk of silent aspiration be viewed as "red-flag" patients by the nursing staff caring for them. Early nursing dysphagia screens, with close attention to the clinical symptoms associated with silent aspiration, and early referral for formal dysphagia evaluation are stressed.


Article Content

Over the past 25 years, a considerable amount of research has been conducted in the area of swallow disorders, aspiration, and aspiration-related medical complications. Although the body of research on aspiration continues to expand, there are less research data available regarding silent aspiration as a unique phenomenon occurring with swallow dysfunction. The prevalence of aspiration following stroke or other neurological disorders has been documented as occurring between 14% and 71%, depending on the diagnosis or lesion site (Doggett, Turkelson, & Coates, 2002; Dusick, 2003; Eibling & Carrau, 2001; Feinberg, Ekberg, Segall, & Tully, 1992; Groher & Bukatman, 1986; Halvorsen, Moelleken, & Kearney, 2003; Horner, Buoyer, Alberts, & Helms, 1991; Keeling et al., 2007; Kelly, Drinnan, & Leslie, 2007; Kendall, Leonard, & McKenzie, 2004; Leder & Espinosa, 2002; Logemann, 1985; Mann, Hankey, & Cameron, 2000; Marik & Kaplan, 2003; Ramsey, Smithard, & Kalra, 2003; Rosenbek, McCullough, & Wertz, 2004; Rosenthal, Lewin, & Eisbruch, 2006; Schindler & Kelly, 2002; Simental & Carrau, 2004; Westergren, 2006; Yoshikawa et al., 2005). Silent subglottic aspiration has been reported in the literature far less frequently (Arvedson, Rogers, Buck, Smart, & Msall, 1994; Horner & Massey, 1988; Kikuchi et al., 1994; Linden, Kuhlemeier, & Patterson, 1993; Ramsey, Smithard, & Kalra, 2005; Ramsey et al., 2003; Smith, Logemann, Colangelo, Rademaker, & Pauloski, 1999; Splaingard, Hutchins, Sulton, & Chaudhuri, 1988).


We define silent aspiration as passage of food or liquids through and below the level of the true vocal folds, without producing a reflexive cough or other overt signs that aspiration has occurred. In the normal larynx, unilateral sensory stimulation will evoke reflexive adduction of the vocal folds. The sensory signal is carried via the superior laryngeal nerve, and the bilateral motor response is carried via the recurrent laryngeal nerves (Blitzer, 1990). If there is a decreased or absent sensory signal, foreign material in the supraglottis and glottis may escape detection and fail to trigger laryngeal closure. Without laryngeal closure, swallowed material may spill through the glottis until it is detected by sensory fibers of the recurrent laryngeal nerve, which provides sensation over the undersurface of the vocal folds and subglottis. If the vocal sensory fibers are also impaired, a cough may not be initiated, and foreign material will descend into the tracheobronchial tree until it provokes a delayed response from the tracheal fibers.


Evaluation of swallow dysfunction, aspiration, and the detection of silent aspiration is largely done utilizing the modified barium procedure, which is a video fluoroscopic examination of the anatomy and physiology of the swallow, widely utilized for over several decades, and is considered the "gold standard" of swallow assessment. Many other evaluation techniques are utilized to assess swallow dysfunction. Fiberoptic endoscopic evaluation demonstrates a 90% agreement with video fluoroscopic evaluation for the detection of aspiration (Donzelli, Brady, Wesling, & Theisen, 2005; Hiss & Postma, 2003; Kelly, Leslie, Beale, Payten, & Drinnan, 2006; Langmore, Schatz, & Olson, 1991; Leder, Acton, Lisitano, & Murray, 2005; Leder, Novella, & Patwa, 2004; McGowan, Gleeson, Smith, Hirsch, & Shuldham, 2007; Perlman et al., 2004). Scintigraphic detection of salivary aspiration, utilizing radioactive technetium and computerized scintillation counter measures, has been reported (Argon et al., 2004; Humphreys et al., 1987; Muz, Mathog, Miller, Rosen, & Borrero, 1987; Ravelli, Panarotto, Verdoni, Consolati, & Bolognini, 2006; Siraj, McClenahan, & Hilson, 2004). Manometry (Goeleven, Robberecht, Sonies, Carbonez, & Dejaeger, 2006; Higo, Tayama, Watanabe, Nitou, & Ugawa, 2003b; McConnel, Cerenko, Jackson, & Hersh, 1988), electromyography (Cook et al., 1989), ultrasound (Shawker, Sonies, Hall, & Baum, 1984), and pulse oximetry (Higo, Tayama, Watanabe, & Nito, 2003a; Leder, 2000; Wang, Chang, Chen, & Hsiao, 2005) have been utilized in research but provide less specific information regarding aspiration and silent aspiration.


Clinical bedside swallow assessments have been utilized with varying levels of success in identifying aspiration secondary to the element of silent aspiration. These assessments are generally performed by giving the patient food textures and varying thicknesses of liquids and observing for clinical signs of distress such as coughing, gagging, throat clear response, and wetness in the patients vocal quality (Aviv, 2002; Belafsky, Blumenfeld, LePage, & Nahrstedt, 2003; Borr, Hielscher-Fastabend, & Lucking, 2007; Daniels, Ballo, Mahoney, & Foundas, 2000; DeMatteo, Matovich, & Hjartarson, 2005; Depippo, Holas, Reding, Mandel, & Lesser, 1994; Hudspeth, Holden, & Crawford, 2006; Leslie, Drinnan, Finn, Ford, & Wilson, 2004; McCullough et al., 2005; McCullough, Wertz, & Rosenbek, 2001; Miyazaki, Arakawa, & Kizu, 2002; Perry & Love, 2001; Splaingard et al., 1988; Tohara, Saitoh, Mays, Kuhlemeier, & Palmer, 2003; Trapl et al., 2007).


The purpose of this research was to expand our understanding of aspiration, with a focus on silent aspiration incidence and prevalence. The study included 2,000 patients with varied neurological pathologies. Ultimately, the authors hope to increase awareness among primary neuroscience nurses and frontline nurses who are a key factor in early detection and referral of suspected dysphagia patients.


Participants and Methods


The swallowing function of 2,000 sequential patients was evaluated by video fluoroscopic examination over a period of 3 years. Ages ranged from 13 to 102 years, with a mean age of 74.1 years and a standard deviation of 15.4 years. There were 1,051 female participants (52.6%) and 949 male participants (47.4%). Ethnicity was 90.8% European American, 4.5% African American, 2.9% Asian American, and 1.8% Hispanic American. All evaluations were conducted in an acute care hospital. All patients were referred for swallow evaluations by their physicians because of concern regarding the safety of their swallow function. Figure 1 shows the varied diagnostic categories for the participants, broken down by diagnosis: nonspecific swallow complaint (e.g., "Things get stuck"), n = 247; left hemisphere stroke, n = 235; right hemisphere stroke, n = 202; transient ischemic attack, n = 126; brainstem stroke, n = 59; pneumonia admit, n = 202; neurodegenerative disease, n = 121; dementia/Alzheimer, n = 106; craniotomy, n = 116; heart related (myocardial infarction [MI]), n = 105; chronic obstructive pulmonary disease (COPD), n = 92; closed head injury, n = 88; seizure, n = 40; syncope, n = 38; head-neck cancer, n = 27; brain cancer, n = 19; generalized weakness, n = 53; and "other," n = 124.

Figure 1 - Click to enlarge in new windowFIGURE 1 All Patients by Admit Diagnosis and Aspiration (


A retrospective study was conducted for a sequential sample of 2,000 patients who were referred by their physicians to assess swallow function and to determine aspiration status. A waiver of informed consent was granted by the institutional review board associated with the hospital conducting the study.


The swallow evaluations were completed at an acute care hospital over a 3-year period. The standard swallow evaluation procedure consisted of five 5-ml doses of pureed/pudding barium paste material, five 5-ml doses of "honey" consistency thickened barium liquid, five 5-ml doses of "nectar" consistency thickened barium liquid, and five sips of thin barium liquid. Solid textures were also given as appropriate to the patient's level of function. Data regarding solid texture were not included in the study. Swallow results were reviewed and discussed jointly by the speech language pathologist (SLP) and radiologist.


Descriptive analyses were provided for all variables. Chi-square tests were used to detect an association between categorical variables (gender, ethnicity, and diagnosis), whereas an independent sample t test was used for age comparison between groups. All analyses were done using Statistical Package for the Social Sciences (Version 15 for Windows). A p value of <.05 was considered statically significant.



Of the 2,000 patients referred for video fluoroscopic evaluation, 50.6% aspirated (n = 1,012). Of those who aspirated, the most common diagnoses were right and left strokes and pneumonia admits (Figure 1). Of the 1,012 patients who aspirated, 54.5% (n = 550) aspirated without a cough reflex; 25.9% (n = 262) aspirated with an immediate cough reflex at the vocal folds (recurrent laryngeal nerve); and 19.6% (n = 198) aspirated with a delayed vagal-tracheal cough reflex. Another 11.4% of patients (n = 227) had laryngeal penetration above the vocal folds that was at risk for aspiration.


No statistical difference related to ethnicity wa noted for patients who aspirated. A significant difference (p = .005) was noted by gender, with male participants aspirating at 54.1% and female participants aspirating at 47.5%. Age was also statistically significant; the average age of those who aspirated was 74.9 years compared with 73.3 years for those who did not (p = .023). Analysis of all patients referred (Figure 1) showed the highest aspiration rates with brainstem stroke (58/59, 98.3%), right hemisphere stroke (158/202, 78.2%), head-neck cancer (21/27, 77.8%), COPD/pulmonary (64/92, 69.6%), dementia/Alzheimer (72/106, 67.9%), closed head injury (59/88, 67.0%), neurodegenerative pathologies (76/121, 62.8%), and craniotomies (72/116, 62.1%).


Analysis of all patients who aspirated without a protective cough reflex (silent aspiration; Figure 2) indicated that the highest silent aspiration rates occurred with brain cancer (9/11, 81.8%), brainstem stroke (46/58, 79.3%), head-neck cancer (16/21, 76.2%), pneumonia admit (78/113, 69.0%), COPD/pulmonary (44/64, 68.8%), dementia/Alzheimer (49/72, 68.1%), seizures (6/9, 66.7%), heart related (20/34, 58.8%), neurodegenerative (41/76, 53.9%), right hemisphere stroke (80/157, 51.0%), closed head injury (28/58, 48.3%), transient ischemic attack (15/37, 40.5%), and left hemisphere stroke (52/129, 40.3%). Clinical symptoms associated with silent aspiration were wet, phlegmy vocal quality, lack of speech, dysarthria of speech (slurring), difficulty controlling secretions (drooling), lack of cough on command, and absence of gag reflex.

Figure 2 - Click to enlarge in new windowFIGURE 2. Cough Reflex With Aspiration by Admit Diagnosis (

Using a consistent intake presentation procedure starting with puree texture, "honey" consistency thickened liquids, "nectar" consistency thickened liquids, and thin liquids, the examination was terminated on the first level of intake aspirated secondary to risk for further aspiration on thinner substances. For example, if aspiration occurred with puree texture, no further intake was given. The examination would continue until aspiration was noted on ensuing substances. In terms of type of food or liquid aspirated, 0.3% aspirated on puree texture, 33.6% aspirated on "honey" consistency thickened liquid, 31.6% aspirated on "nectar" consistency thickened liquids, and 34.5% aspirated only on thin liquids.


The movement pattern of the epiglottis to protect the airway was examined in terms of relationship to aspiration. Seventy percent of patients who aspirated had a delayed epiglottic inversion to protect the airway, and 30% of aspirators had an abnormal epiglottic movement pattern. Of all patients who aspirated, 70.7% were placed on a modified oral diet and 28.5% received recommendations for nonoral nutritional intake via enteral (G-J tube or nasal feeding tube) or parenteral nutrition.



In an analysis of pathologies highly associated with silent aspiration, the following diagnostic groups were the most highly related to a lack of protective cough reflex: brain cancer, brainstem stroke, head-neck cancer, pneumonia admit, dementia/Alzheimer, COPD/pulmonary, seizures, heart-related (MI), neurodegenerative (e.g., Parkinson and multiple sclerosis), right hemisphere stroke, closed head injury, and left hemisphere stroke. Patients with silent aspiration are in a higher risk group for the development of pneumonia or complications because the lack of cough reflex reduces patient, family, and hospital staff awareness that aspiration is occurring. This lack of awareness of aspiration can lead to a longer period of ingestion of food and liquids into the lungs, potentially elevating the risk for development of complications. Many pneumonia patients, for example, are treated with antibiotics for many days without medical progress. If these patients have silent aspiration, they are continually, unknowingly ingesting food and liquids into their lungs in a manner which is not detectable to staff, which is countereffective to the medical therapy being provided.


The pulmonary effects of chronic aspiration, aside from the development of aspiration pneumonia, can be extensive. Anatomic and physiological changes occur in the aging lung that affect the lung's ability to function. Airway size is reduced due to alterations in the supportive connective tissue that helps to keep the airway open (Zaugg & Lucchinetti, 2000). These anatomical changes result in the following physiological changes: (a) decreased elastic recoil, (b) reduced diffusion capacity for oxygen and carbon monoxide, (c) premature airway closure associated ventilation-perfusion mismatch, and (d) reduced expiratory flow (Chan & Welsh, 1998). The lung's ability to clear particles from small airways appears to decrease with age (Svartengren, Falk, & Philipson, 2005). The rate of mucociliary clearance is reduced in elderly participants, as is the lung immune response and the ability to fight infections (Meyer, 2001).


Most patients who are admitted to the acute care hospital with strokes or an ongoing neurodegenerative process are placed in a compromised position by their admit pathology, and this can be worsened by reducing their ability to breathe secondary to aspiration or silent aspiration affecting the physiology of their respiratory system.


It is interesting to note that only 20% of patients who were referred with a generic swallow complaint, for example, "things get stuck," were aspirators. Most of these patients were found to have esophageal disorders, reflux disease, hiatal hernias, Zenker diverticulae, strictures, or spasms. Many had complaints of dry mouth or throat, often medication related. We would recommend a traditional esophagram study with this population, possibly in conjunction with a video fluoroscopic swallow evaluation to evaluate the entire swallow process, from oral to pharyngeal to esophageal physiology.


It is important to view the data obtained in this study as a sample of each pathology-etiology group. It should be analyzed with the knowledge that patients were referred for swallow evaluation by their physician secondary to concern regarding the safety of their swallow function. One should not view the aspiration or silent aspiration results of this study as indicative of all persons with that given pathology. For example, the Parkinson patients who were referred for evaluation were a subset of all Parkinson patients in the acute hospital, who in turn were a subset of all Parkinson patients.


One area of future research that we feel is important to study concerns pneumonia admits. It would be of interest to compare patients who received medical therapy only with patients who received swallow evaluations early after admit to assess aspiration status both in terms of patient recovery and with length of stay and costs involved with medical care.


It is critical that nurses understand the nuances associated with recognizing silent aspiration. Multiple bedside screening tools and methods (Westergren, 2006) are available to assist in identification of patients who aspirate. Obvious responses to these screens are choking, coughing, and throat clear response. The more subtle signs of silent aspirators are easier to miss. These include wet, phlegmy vocal quality, lack of speech, depressed alertness level, drooling, difficulty controlling secretions, and absence of gag reflex. In performing their assessments, nurses must raise their index of suspicion with patients in the "red-flag" diagnostic groups. They should collaborate with the SLP to determine the need for formal evaluation using video fluoroscopic or fiberoptic endoscopic examination.


Swallow impairment and the need for dysphagia screening are often associated with patients with a primary neurological diagnosis such as stroke or dementia. However, these data demonstrate that patients without a primary neurological diagnosis such as MI, pneumonia, and COPD are also at risk. Awareness is the first step, but then the nurse must act and refer the patient to the SLP for more extensive assessment and evaluation. The need for ongoing assessment cannot be overemphasized. Reevaluation via repeat dysphagia screening or formal assessment by the SLP should take place at any point during the patient's hospital stay when there is suspicion of deterioration in the patient's status.



In addition to the efforts of the swallow team members on this research, we would like to extend our gratitude and thanks to the St. Paul Radiology, PA, physicians; the St. Joseph's Hospital radiology technicians; as well as Amy Fehrer, Susan Mehle, Penny Tatman, and other members and volunteers in the HealthEast Research and Education Department.




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