Selecting and Preparing Colorants for Endoscopic Swallowing Assessments

WHICH COLORANTS SHOULD YOU USE DURING FEES?

Based off the research described below, I recommend using two types of liquid boluses during a standardized FEES protocol: (1) heavily-concentrated white-dyed water; and (2) blue or green, opaque water. As described below, the types of contrasts used during FEES can significantly influence the detection of functional swallowing impairment (pharyngeal residue, penetration, and aspiration). Therefore, it is important to standardize what types of contrasts are used during FEES and SEES to ensure the validity and reliability of the endoscopic swallowing assessment. Three contrast properties that have been previously researched as they relate to detecting pharyngeal residue, penetration, and aspiration during FEES include 'color', 'coating', and 'opacity.' 

COLOR

The effect of color has been studied the most as it relates to detecting of functional swallowing impairments during FEES. Three studies examined the reliability of rating functional impairments as an effect of food dye. Research comparing blue-dyed milk to naturally white (non-dyed) milk found inter-rater reliability to be descriptively higher for the naturally white milk for ratings of pharyngeal residue, penetration, and aspiration (Leder et al., 2005). Research comparing green-dyed milk to naturally white (non-dyed) milk found rater reliability to be greater for the green-dyed milk for ratings of penetration/aspiration (Marvin et al., 2016). Lastly, research comparing reliability of barium water, blue-dyed water, and green-dyed water found reliability to be highest for green-dyed water and barium, and lowest for the blue-dyed water (Curtis et al., 2019). 

Three studies have examined the effects of color on ratings of functional swallowing outcomes for thin liquid boluses during FEES. In a study comparing green-dyed milk to naturally white (non-dyed) milk, more severe penetration-aspiration  was observed more frequently for the green-dyed milk compared to the naturally white milk (Marvin et al., 2016). In a study comparing green- and blue-dyed water, no differences in detection rates were observed between blue- and green-dyed water (Curtis et al., 2019). In a study comparing blue-dyed milk to naturally white (non-dyed) milk, pharyngeal residue and penetration-aspiration were seen more frequently with blue-dyed milk compared to naturally white milk (Curtis et al., 2021). 

One study has examined the effects of puree type and color on pharyngeal residue, penetration, and aspiration during FEES. This study found: (1) pudding boluses had greater amounts of pharyngeal residue than applesauce boluses; (2) blue-colored applesauce had greater amounts of oropharyngeal and hypopharyngeal residue than non-colored applesauce; and (3) green-colored applesauce and green-colored pudding had greater amounts of hypopharyngeal residue than non-colored applesauce or non-colored pudding (Curtis et al., 2024). 

Together, these data suggest that, from a color standpoint, green may the most reliable and sensitive color for assessing functional swallowing impairments during FEES, followed by white and blue respectively - though the differences between colors (i.e., their effect size) appear relatively small.

COATING

The effects of coating has been directly researched in one study (Curtis et al., 2021) and indirectly researched in a second study (Curtis et al., 2019). In both studies, liquids containing a coating effect (heavily concentrated white-dyed water, barium water) were seen substantially more frequently compared to other liquids. Coating appears to have a very large effect on the detection of pharyngeal residue, penetration, and aspiration during FEES, compared to the relatively small effects of color and opacity. Therefore, data suggest that coating is the most important contrast property for assessing functional swallowing impairments during FEES. Because of this, it is important to ensure that each swallow condition examined during FEES includes at least one trial using a contrast that possesses a coating effect. 

So, what types of liquids contain a coating effect? Our 2021 study compared heavily concentrated white-dyed water, barium water, naturally white milk, blue-dyed milk, and blue translucent water to identify which types of liquid boluses exhibited a coating effect most frequently. This study found heavily concentrated white-dyed water exhibited a perceived coating effect for ~96.7% of thin liquid swallows, compared to 80% of barium water swallows, 13.3% of blue water swallows, 6.7% of white milk swallows, and 0% of blue milk swallows. 

OPACITY

The effect of opacity on the detection of pharyngeal residue, penetration, and aspiration has been directly studied in one study whereby blue-dyed milk (opaque) was compared to blue-dyed water (translucent/non-opaque) (Curtis et al., 2021). The effects of opacity have indirectly research in several other studies whereby dyed-waters were compared to dyed milk or barium but where opacity wasn't a central research question (e.g., Curtis et al., 2019; Butler et al., 2018). Together, these studies found small effects of opacity on the detection of functional swallowing impairments, with pharyngeal residue, penetration, and aspiration observed more frequently for liquids that were opaque compared to non-opaque. 

SUMMARY OF FINDINGS

Coating is the most important contrast property for detecting pharyngeal residue, penetration, and aspiration during FEES. It is reliable and sensitive and demonstrates a large effect size. Color and opacity also influence the detection of functional swallowing impairments, albeit to a lesser extent than coating.

CLINICAL TIPS  AND ANECDOTES

A standardized FEES protocol should include multiples trials for each swallowing conditions. Given the above research, I recommend having one trial within each liquid swallowing condition be heavily-concentrated white dyed water and another trial within each liquid swallowing condition be a colored-opaque liquid with minimal-to-no coating effect. 

Having one trial within each swallowing condition be a heavily concentrated white-dyed water will maximize sensitivity and reliability of detecting pharyngeal residue, penetration, and aspiration.  However, one problem with coating effect liquids is that over time the dye/barium can coat ("gunk") the camera lens, significantly impacting visualization. Furthermore, it can be difficult to discern if coating residue is new or old. Because of that, you may consider including sips of clear water to assist in clear coating. You may also consider alternating bolus with coating with boluses that have minimal-to-no coating effect, and also altering between different colors to help discern which residue is from which bolus trial.

For opaque-colored liquids, I recommend using water, green or blue dye (to give it color),  and a little bit of white dye (to make it opaque).  Limiting the white dye to just a few drops should not elicit a significant coating effect. Using water avoids pragmatic issues associated with using milk (e.g., dietary restrictions, refrigeration, costs). Using opaque-colored liquids with minimal-to-no coating effect will help to wash away coating on the mucosa and camera lens from previous trials. Because the bolus is colored green/blue, it will be easier to discern new residue is new (blue/green) from coating-related residue (white). And because the bolus is opaque, it will maximize the sensitivity and reliability compared to using something completely translucent. You may also consider integrating sips of clear water between liquid trials to clear residue from previous swallows an ultimately enhance accuracy of FEES interpretation.

For puree boluses, I recommend using pudding, since this more closely resembles the consistency also used during VFSS. Chocolate pudding may be avoided since it is darker and more difficult to visualize. Vanilla pudding is more easily visible, but can be difficult to discern from thick secretions or white liquid residue. Therefore, you may consider adding food dye to help discern pudding residue from secretions and liquid residue.

REFERENCES

1. Curtis, J. A., Rameau, A., & Mocchetti, V. Effects of Puree Type and Color on Ratings of Pharyngeal Residue, Penetration, and Aspiration during FEES: A Prospective Study of 37 Dysphagic Outpatient Adults. Folia Phoniatrica et Logopaedica, 1-16

2. Curtis, J. A., Seikaly, Z. N., Dakin, A. E., & Troche, M. S. (2021). Detection of aspiration, penetration, and pharyngeal residue during flexible endoscopic evaluation of swallowing (FEES): comparing the effects of color, coating, and opacity. Dysphagia, 36(2), 207-215

3. Curtis, J., Perry, S., & Troche, M. S. (2019). Detection of airway invasion during flexible endoscopic evaluations of swallowing: comparing barium, blue dye, and green dye. American journal of speech-language pathology, 28(2), 515-520 

4. Butler, S. G., Stuart, A., Markley, L., Feng, X., & Kritchevsky, S. B. (2018). Aspiration as a function of age, sex, liquid type, bolus volume, and bolus delivery across the healthy adult life span. Annals of Otology, Rhinology & Laryngology, 127(1), 21-32

5. Marvin, S., Gustafson, S., & Thibeault, S. (2016). Detecting aspiration and penetration using FEES with and without food dye. Dysphagia, 31(4), 498-504.

6. Leder, S. B., Acton, L. M., Lisitano, H. L., & Murray, J. T. (2005). Fiberoptic endoscopic evaluation of swallowing (FEES) with and without blue-dyed food. Dysphagia, 20(2), 157-162.