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Weekly UpdatesABSTRACT
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.
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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 (DoggeR, 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; Homer & 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 Participants
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; fight 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.
Methods
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.
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Results
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 fight 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.
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