Carbonation as a sensory enhancement strategy: evidence for clinical implementation

Abstract

Speech Pathologists sometimes use sensory enhancement strategies (SES) as an option to help reduce symptom severity and improve swallow safety in individuals with dysphagia (disordered swallowing). SES involve altering the taste, temperature or other sensory properties of food or liquid. Current anecdotal evidence suggests clinicians are highly variable in their use of SES in dysphagia management. The use of SES in dysphagia management was first advocated by Logemann in the original manual for conducting videofluoroscopic swallow studies (VFSS) in 1993. Despite over 26 years since that initial seminal work, there remains limited understanding of how SES are used in clinical practice. In particular, processes and procedures for testing SES including during instrumental assessments remain poorly described and understood. Research trials of SES strategies published to date are limited in number, highly variable in study design, and have revealed both potential positive and negative impacts on dysphagia symptoms from specific SES strategies (Pauloski et al., 2016). In order to help move towards development of evidence-based standards of care, there is a need for more systematic research into SES use within the clinical setting, and greater understanding of the impact of SES on dysphagia symptoms (Butler et al., 2016). To this end, this PhD thesis describes four key aspects of research inquiry, all conducted within the area of SES, with a specific focus on the use of carbonation.The introductory chapter of this thesis (Chapter 1), provides the background and rationale for the investigation of SES use in dysphagia management. An overview of healthy and disordered swallowing precedes a summary of current SES research. A justification for the selection of carbonated liquids as the specific SES for systematic investigation is then provided. Chapter 2 presents the first research study, a narrative synthesis of existing evidence related to the use of carbonated liquids as a SES. A narrative synthesis methodology was chosen given the exploratory level and disparate nature of evidence related to carbonation as a SES in dysphagia management. Identifying only fifteen relevant papers, this synthesis outlined a number of issues with the current evidence, contributing to a lack of clear direction for the clinical implementation of carbonation.Chapter 3 contains the results of a qualitative research study conducted to examine current SES use in Australian VFSS clinics. Information was obtained via semi structured interviews with focus groups of VFSS clinicians (N = 16). Key findings from this work revealed four themes emerging as influencing drivers of SES use including: patient factors, clinician factors, trials of SES requiring planning and organisation, as well as organisational barriers. The four themes were all connected through a single integrative theme relating to the extensive variation of clinical practice related to SES use. The findings confirmed practices amongst clinicians are variable regarding SES use during VFSS and general dysphagia management. A stronger evidence base is needed to inform clinical practice.Information obtained from the narrative synthesis (Chapter 2) and qualitative study (Chapter 3) then helped to inform the methodological design of the two final studies. Chapter 4 presents findings from a prospective cohort study (N = 29) which examined the efficacy of the use of carbonated liquids to reduce symptoms of neurogenic dysphagia using VFSS. A secondary analysis of patient factors influencing the impact of carbonation within this neurogenic dysphagia cohort was also conducted. As a cohort, a significant reduction in neurogenic dysphagia symptoms was observed with trials of carbonation during videofluoroscopy. However, separate analysis of each participant revealed individual variability in response to carbonation. Furthermore, no clear pattern of clinical predictors for a positive response to carbonation was identified. The final thesis study (Chapter 5) was a healthy cohort study, comparing different carbonated VFSS liquids used to test carbonation (as previously described by clinicians in Chapter 3). Taste intensity, palatability, effervescence, and sip volumes of different carbonated VFSS stimuli were examined in a cohort of healthy females. The cohort (N = 44) comprised participants who were defined as either super-taster (n = 22) or non-taster (n = 20). Results revealed significant differences in palatability, taste intensity and effervescent behaviour between liquids.The body of work in this thesis provides further evidence to help inform the use and increase understanding of the efficacy of using carbonation as a SES for individuals with neurogenic dysphagia. Thesis findings highlight current challenges for clinicians who attempt to use carbonation as a SES in neurogenic dysphagia management including during VFSS. The challenges include the emerging and changing understanding of processes related to carbonation perception, minimal understanding of optimal methods of testing carbonation within VFSS and significant variability identified in response to carbonation of individuals with neurogenic dysphagia. These issues are all discussed in the final chapter (Chapter 6) in relation to clinical implications, along with areas of research required to facilitate progression towards more evidence-based use of carbonation as a SES in the future.