Viscosity of thickened fluids that relate to the Australian National Standards

Abstract

Purpose: In 2007, Australia published standardized terminology and definitions for three levels of thickened fluids used in the management of dysphagia. This study examined the thickness of the current Australian National Fluid Standards rheologically (i.e. viscosity, yield stress) and correlated these results with the “fork test”, as described in the national standards.

Method: Clinicians who prescribe or work with thickened liquids and laypersons were recruited to categorize 15 different thickened fluids of known viscosities using the fork test. The mean apparent viscosity and the yield stress for each fluid category were calculated.

Result: Clear responses were obtained by both clinicians and laypersons for very thin fluids (< 90 mPa.s) and very thick fluids (> 1150 mPa.s), but large variations of responses were seen for intermediate viscosities. Measures of viscosity and yield stress were important in allocating liquids to different categories.

Conclusion: Three bands of fluid viscosity with distinct intermediate band gaps and associated yield stress measures were clearly identifiable and are proposed as objective complements to the Australian National Standards. The “fork test” provides rudimentary information about both viscosity and yield stress, but is an inexact measure of both variables.

Keywords:

• Dysphagia
• thickened fluids
• fluid standards

Acknowledgements

The authors would like to formally acknowledge Nestlé Health Science, Australia for funding this project as part of a PhD program. The funding organization was not involved in the design of the project, its conduct or the writing and interpretation of the results. None of the authors have a financial interest in the sponsor company. The sponsor had no input into the preparation or approval of the manuscript. The authors also would like to acknowledge the input and support provided by the School of Chemical Engineering, The University of Queensland, Centre for High Performance Polymer Processing (CHPP-P), Andrea Whitehead (Senior Speech Pathologist, Mater Health Services), Sarah Heaton (Speech Pathology Team Leader in Royal Brisbane & Women’s Hospital) and to all participants (68) in this study.