Effect of Bolus Viscosity on the Safety and Efficacy of Swallowing and the Kinematics of the Swallow Response in Patients with Oropharyngeal Dysphagia: White Paper by the European Society for Swallowing Disorders (ESSD)

Abstract

Background: Fluid thickening is a well-established management strategy for oropharyngeal dysphagia (OD). However, the effects of thickening agents on the physiology of impaired swallow responses are not fully understood, and there is no agreement on the degree of bolus thickening.

Aim: To review the literature and to produce a white paper of the European Society for Swallowing Disorders (ESSD) describing the evidence in the literature on the effect that bolus modification has upon the physiology, efficacy and safety of swallowing in adults with OD.

Methods: A systematic search was performed using the electronic Pubmed and Embase databases. Articles in English available up to July 2015 were considered. The inclusion criteria swallowing studies on adults over 18 years of age; healthy people or patients with oropharyngeal dysphagia; bolus modification; effects of bolus modification on swallow safety (penetration/aspiration) and efficacy; and/or physiology and original articles written in English. The exclusion criteria consisted of oesophageal dysphagia and conference abstracts or presentations. The quality of the selected papers and the level of research evidence were assessed by standard quality assessments.

Results: At the end of the selection process, 33 articles were considered. The quality of all included studies was assessed using systematic, reproducible, and quantitative tools (Kmet and NHMRC) concluding that all the selected articles reached a valid level of evidence. The literature search gathered data from various sources, ranging from double-blind randomised control trials to systematic reviews focused on changes occurring in swallowing physiology caused by thickened fluids. Main results suggest that increasing bolus viscosity (a) results in increased safety of swallowing, (b) also results in increased amounts of oral and/or pharyngeal residue which may result in post-swallow airway invasion, (c) impacts the physiology with increased lingual pressure patterns, no major changes in impaired airway protection mechanisms, and controversial effects on oral and pharyngeal transit time, hyoid displacements, onset of UOS opening and bolus velocity-with several articles suggesting the therapeutic effect of thickeners is also due to intrinsic bolus properties, (d) reduces palatability of thickened fluids and (e) correlates with increased risk of dehydration and decreased quality of life although the severity of dysphagia may be an confounding factor.

Conclusions: The ESSD concludes that there is evidence for increasing viscosity to reduce the risk of airway invasion and that it is a valid management strategy for OD. However, new thickening agents should be developed to avoid the negative effects of increasing viscosity on residue, palatability, and treatment compliance. New randomised controlled trials should establish the optimal viscosity level for each phenotype of dysphagic patients and descriptors, terminology and viscosity measurements must be standardised. This white paper is the first step towards the development of a clinical guideline on bolus modification for patients with oropharyngeal dysphagia.

Keywords: Deglutition; Deglutition disorders; Kinetics; Review; Rheology; Viscosity.

Fig. 1

A summary of the reviewing process showing inclusion and exclusion criteria

Fig. 2

Prevalence of patients with laryngeal penetration (measured by VFS or FEES) according to the viscosity levels cited in the literature. Note the viscosity-dependent reduction in the prevalence of penetration with maximal therapeutic effect at spoon-thick viscosity

Fig. 3

Prevalence of patients with aspiration (measured by VFS or FEES) according to the level of viscosity cited in the literature. Note the overall viscosity-dependent reduction on the prevalence of aspiration with maximal therapeutic effect at spoon-thick viscosity

Fig. 4

Effect of bolus viscosity on the prevalence of safe swallows in patients with OD cited in the literature. a the viscosity-dependent increase in the safety of swallow; b the strong therapeutic effect of spoon-thick viscosity. The patient phenotypes in this group varied widely and included healthy volunteers; older persons; stroke patients; and patients with neurological tumour; neurodegenerative diseases; unilateral vocal cord palsy secondary to malignancy, surgery or intracranial causes; and general illness including urinary tract infection, respiratory disorders, heart failure, chronic renal failure and cerebrovascular disease; c various agents were used to modify the viscosity of the fluid boluses in each study, including XG, MS and barium sulphate

Fig. 5

This graph shows the mean value of PAS score at each viscosity. We can see that increasing bolus viscosity significantly reduced PAS scores; lower PAS scores refer to less impaired swallowing, whereas higher scores indicate increased risk of penetration and/or aspiration of boluses