Comparison of two methods to categorize thickened liquids for dysphagia management in a clinical care setting context: The Bostwick consistometer and the IDDSI Flow Test. Are we talking about the same concept?

Abstract

The Bostwick consistometer and the International Dysphagia Diet Standardization Initiative (IDDSI) Flow Test are both proposed methods to measure and categorize thickened liquids for dysphagia management. The objectives were to: (a) compare the Bostwick consistometer reference values used in clinical settings and the IDDSI reference values of thickened liquids suggested for nutrition care plans in the management of dysphagia when measuring commercially available preprepared thickened liquids; (b) explore the relationship between the two methods; (c) assess the interchangeability; (d) document the intra‐rater reliability. Preprepared thickened liquids (n = 32) were measured twice with the Bostwick consistometer and 3 times with the IDDSI Flow Test, using a rigorous methodology. A registered dietitian nutritionist and a registered nutrition and dietetic technician performed the measurements. The Pearson's correlation coefficient was calculated to explore the relationship between the two methods. Using a linear regression equation, back‐calculations of the IDDSI Flow Test values were done, based on the experimental Bostwick results. Interchangeability was assessed by documenting the level of agreement between the results with a Bland and Altman graphical analysis. Intraclass correlation coefficients calculation and a Bland and Altman graphical analysis were performed to assess reliability. The strong correlation (r = −.93, p < .001) between the IDDSI Flow Test and the Bostwick consistometer measurements suggests that they measure flow rate in a similar manner, but not exactly the same, as confirmed with the Bland and Altman graphical analysis. Thus, they produced results that are not interchangeable. However, both tests show excellent intra‐rater reliability (ICC ≥ 0.99) when using a rigorous methodology. Practical applications Thickened liquids are used to manage oropharyngeal dysphagia. Clinicians need to provide quality assurance/quality control (QA/QC) support in the selection or production of thickened liquids as well as staff training or patient education regarding these products. Methods and classification have been proposed to measure and categorize thickened liquids for dysphagia management, such as the line spread test, the Bostwick consistometer method, and the IDDSI Flow Test. Although empirical, these methods are more accessible to clinicians than viscometer or rheometer assessments. Clinicians need to understand the limitations of these techniques as neither appear to capture the full extent of consistency for potential beverages available on the market or produced in‐house. In this article, we compare the Bostwick consistometer and the IDDSI Flow Test methods and classifications and propose a standard operating procedure in order to maximize the quality of results. We point out the large variations in consistency levels of commercial preprepared thickened liquids in light of the absence of evidence of clinical outcomes associated with either proposed methods or consistency classifications.

Are Medication Swallowing Lubricants Suitable for Use in Dysphagia? Consistency, Viscosity, Texture, and Application of the International Dysphagia Diet Standardization Initiative (IDDSI) Framework

“…In fact Severo was the same as Slo Tablets and Medispend in all of the textural features measured, and viscosity (0.47 Pa.s) was also in the range measured for IDDSI level 3 dysphagia-oriented products (0.25 to 0.6 Pa.s) rather than level 2 (0.08 to 0.2 Pa.s) [ 35 ]. However, it flowed quickly in the Bostwick consistometer (21.1 cm in 30 s), well within the range measured for level 2 dysphagia-oriented products (16.7 to 22.2 cm) [ 23 ]. In a swallowing study involving 120 patients with oropharyngeal dysphagia, only 25 safely completed a series of three swallows of a thin liquid (5 mL, 10 mL, 20 mL), with other 95 patients exhibiting voice changes, cough or oxygen desaturation [ 9 ].…”

“…We believe that this property is associated with the noticeably lower yield stress (1.6–2.5 Pa). It is difficult to directly compare yield stress values in the literature because the method of measurement affects the outcome; however, we are confident that the yield stress values we measured for these products were certainly more characteristic of IDDSI level 2 fluids (nectar/quarter/mildly thick) than level 3 fluids (honey/half/moderately thick) measured in other studies [ 23 , 40 , 41 ]. We were unable to measure a yield stress for the IDDSI level 2 product, Severo, which is not unusual for materials thickened with cellulose [ 42 ].…”

“…Indeed, the room temperature Gloup measurements for viscosity (0.6–0.9 Pa.s) were more similar to dysphagia-oriented products that classify as IDDSI level 4 (0.64 to 3.78 Pa.s) than level 3 (0.25 to 0.6 Pa.s) [ 35 ]. Additionally, Gloup products flowed in a Bostwick consistometer (5–8 cm in 30 s) at a rate that was more similar to IDDSI level 4 dysphagia-oriented products (7.3 to 8.6 cm) than level 3 (8.3 to 18.9 cm) [ 23 ].…”

“…Traditional rheometry measurements of the samples used in this study provided their viscosity as 0.45–0.42 Pa.s, which aligns with the range for other IDDSI level 3 dysphagia-oriented products (0.25 to 0.6 Pa.s) [ 35 ]. Assessment of MediSpend and Slo Tablets using the Bostwick consistometer (15–17 cm in 30 s) was at the faster end of the flow range (8.3 to 18.9 cm in 30 s) measured for dysphagia-oriented liquids that classify as IDDSI level 3 according to the IDDSI Flow test [ 23 ]. However, their behaviour in the Fork Drip test did not correspond with the requirements for IDDSI level 3 because they were not retained at all by a fork and instead flowed continuously through the prongs.…”

“…Rheological properties (i.e., viscosity and yield stress) provide important information that have a profound effect on swallowing safety [ 21 ], and although there are no standard conditions prescribed for rheological testing, a shear rate of 50 s −1 is commonly used as an indicator of the shear rates of swallowing, which facilitates comparison between studies [ 15 , 22 ]. A Bostwick consistometer has been used to assess the consistency of dysphagia-oriented thickeners by several manufacturers, as it has good reproducibility and offers accessible measurements [ 23 ]. Texture features, such as hardness and adhesiveness, are also characteristics that are considered in some studies because these affect the swallowing process [ 24 ].…”