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Introduction

In the fall of 2015, the International Dysphagia Diet Standardization Initiative (www.iddsi.org) released a new framework for categorization of foods and drinks used for patients with dysphagia. A key element of that framework was the development of a new test for measuring liquid flow using a syringe. This IDDSI Syringe Flow Test is intended to be user friendly and simple, so that it lends itself to use by clinicians, food service staff, caregivers and even patients – enabling quality checks of liquid flow, both at the time of preparation and the time of serving. In the Swallowing Rehabilitation Research Laboratory at the Toronto Rehabilitation Institute, research staff have been using the IDDSI syringe flow test. In this blog post, doctoral student and research coordinator Carly Barbon shares insights gained through her experience with the test.

Question: I understand you have been measuring the flow of various liquids using the IDDSI Syringe Test. What liquids have you tested so far?

I have been testing liquid flow according to the IDDSI guidelines for about two months now. Currently, I have tested thickened barium and non-barium stimuli. I’ve used E-Z-Paque® powdered barium and a lemon flavored water by Nestlé, both mixed with two thickeners produced by Nestlé for the barium stimuli: ThickenUp ®(starch-based thickener) and ThickenUpClear ® (xanthan-gum based thickener). The barium stimuli have been mixed and tested at a 20% weight-to-volume barium concentration. The goal has been to create thickened barium stimuli and matched non-barium stimuli that fall within the different IDDSI levels of flow, measured using the syringe test: thin, slightly thick, mildly thick, moderately thick and extremely thick. We hope to continue this work and to expand to different liquids and different thickeners over the next year.

Question: What do you like the most about the syringe test?

I appreciate the simplicity, speed and accuracy of the test. Using the test for research and clinical purposes is extremely convenient, reliable and user-friendly. A prior knowledge of rheology and flow is not required for the IDDSI test. I also appreciate the fact that the syringe test offers us a new opportunity to match the flow properties of the liquids we use in VFSS to liquids that are available clinically from our hospital kitchen.

Question: How many tests do you run for a particular liquid, to get a sense of how stable or variable its flow is?

In order to ensure accuracy of a syringe flow test result, I have found that it is best to conduct 3-4 tests per liquid using the same batch. This is a good way to measure the variability of the liquid, and it also accounts for human error. If three consecutive runs are within 1mL of each other, I typically stop and take the average of those 3 test results as the measure of flow. However, I have found that liquids (regardless of the thickener or whether barium is involved) can also vary greatly. Therefore, if one of the 3 syringe tests has a result that is more than 1 ml different from the other tests, I will run a 4th test and take the average of 3 closest measures. I have sometimes experienced cases where two back-to-back tests from the same batch have flowed differently. For example, the first run might fall within the slightly thick flow category (leaving 1-4ml in the syringe after 10 seconds), while the second run might flow completely through the syringe prior to the 10 second mark, suggesting that it is a thin liquid. In these cases, it is best to conduct several repeat tests in order to ensure accuracy and to account for variability of the liquid you are testing, along with your own human error.

Question: I know that you have previously learned to measure viscosity on a rheometer.  Can you comment on the differences between making those measurements and measuring liquids using the syringe?

Having measured viscosity on a rheometer for research purposes, I can confirm that it is a more complicated and cumbersome procedure. Specific measurements can be made in terms of shear stress, shear rate, yield stress and modulus. However, it is difficult to translate these parameters into clinically relevant measures. Rheological measurements take a long time and require expensive equipment and training in the methods; this is not practical or accessible in clinical settings. With the IDDSI test, I can use the measures for research purposes and translate them easily for the clinical world.

As speech-language pathologists, we must be able to take our data and use it in a way that will benefit our patients. As a field, we have been striving for the ability to determine the best possible stimulus for a patient under fluoroscopy, and then match these stimuli for the patients in daily life. With the IDDSI syringe flow test, we are able to do just that. We are now able to characterize the flow of a liquid and describe the desired characteristics for patients and their caregivers in a way that makes it possible for them to replicate the liquids at home – and to test them at home, and have confidence that they are serving liquids with the desired thickness. This is the ultimate in knowledge translation for clinical use!

Question: Have any of the syringe test results surprised you?

The variability of flow within a particular liquid is always quite interesting to observe. Ensuring there are no chunks will add to the overall accuracy of the test along with ensuring the liquid has had enough time to thicken, especially if you are using a starch thickener.

If liquids are to be served at room temperature, their flow should also be tested at room temperature. At the same time, if the liquids are to be served refrigerated, they should also be tested after being refrigerated. I have observed temperature variation with each thickener type. The syringe flow test offers this possibility, so now we can monitor whether the thickness of a drink changes as a product cools or warms.

I have found that liquids thickened with a xanthan gum thickener demonstrate fairly stable flow within the same IDDSI range over a 24 hour period. However, I have found that this is difficult to achieve with starch thickeners. In addition, it is important to consider time variations. Starch-thickened liquids are not stable until approximately 20-30 minutes after preparation. One should consider waiting until the thickener has stabilized before testing and serving.

Question: Do you have any tips for clinicians who are planning to use the syringe test?

Lumps

One of the main challenges with syringe testing has been making sure there are no lumps within the stimulus. Even if there are very small lumps floating within the suspension, this can alter or impede the flow of the liquid through the syringe. When this occurs you do not get an accurate measurement of flow. There are a few ways to decrease the risk of having lumps in your stimulus:

  1. Ensure that the liquid is moving at the time you pour the barium and/or thickener into the medium.
  2. While the liquid is moving, either pour the pre-measured barium in, and then the thickener, or pour them into the moving water at the same time.
  3. You can also mix together the pre-measured barium powder with the pre-measured thickener. After combining the two, you can pour this single mixture into the moving water.

Bubbles

Bubbles are also variables that can alter the flow, and the corresponding IDDSI flow test result. When you are using a syringe to draw up a sample of thickened liquids, bubbles can occur if air gets mixed in with the sample. Bubbles are also something that can occur when mixing in a thickener, particularly a gum thickener. In order to prevent bubbles in a test sample, you should make sure that there is enough liquid in the sample you are drawing up to prevent air from entering the syringe. When you then deliver the sample into the flow test syringe, press the nozzle of the loading syringe to the side of the test syringe and make sure to load the sample slowly.

Timers

I find a timer that works using light touch rather than a push button works best. I have experimented with various timers, and have found that button timers are sometimes unreliable. I use the timer on my iPhone and press the start button as I am releasing my pinky finger from the nozzle of the test syringe.

Washing and re-using syringes

If you will be re-using syringes you must make sure they are completely clean and completely dry before use. I always have a sink of hot soapy water that I place my syringes in immediately after testing. Once I have completed a batch of testing, I wash the syringes right away by pumping each syringe with the soapy water approximately 4 times. I rinse each syringe with clean, hot water and leave them to dry. I will not use a syringe if it has any sign of water left, especially in the nozzle.

Question: Are there any other comments you would like to make regarding measuring liquid flow?

Be sure to stir the liquid prior to testing, especially if it contains powdered barium. If the liquid sits for a length of time prior to testing, the barium typically settles to the bottom. Therefore, the flow may be altered due to a decrease in barium within the suspension.

Conclusion

The IDDSI Syringe Flow Test allows the clinician the ability to match flow between videofluoroscopy test stimuli and diet recommendations. It is important to ensure that the syringe meets IDDSI framework standards in order to obtain accurate flow results. IDDSI recommends using the BD slip tip or luer lock 10mL syringe, which meets the requirements of a 61.5 mm chamber length for a 10 ml volume. We recommend conducting repeated tests to obtain a reliable result. In summary, the IDDSI Syringe Flow Test is a quick and accurate way to test the flow of liquids given to patients, both in and out of videofluoroscopy. This will enable clinicians to have greater confidence when making diet recommendations to facilitate safe and efficient swallowing for their patients.

About the Authors

Catriona M. Steele, Ph.D., CCC-SLP, BCS-S, ASHA Fellow is a Professor in the Department of Speech-Language Pathology at the University of Toronto and Director of the Swallowing Rehabilitation Research Laboratory at the Toronto Rehabilitation Institute – University Health Network (www.SteeleSwallowingLab.ca).

Carly Barbon is a third year Ph.D student under the mentorship of Dr. Catriona Steele. She completed her MA in Speech-Language Pathology at Central Michigan University. Her doctoral research combines her experience and interest in head and neck cancer which stem from her time in the head and neck oncology department at the University of Michigan, along with her specific interests in texture modification.

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