The effect of liquid type on the detection of airway invasion during swallow evaluation

Objectives: To explore FEES findings obtained using different liquid types, water, cow’s milk, and soy milk, with respect to observed penetration, aspiration, and pharyngeal residue, and to describe agreement across liquids. Methods: Adult patients referred to a university-affiliated dysphagia clinic underwent standardized FEES using water, cow’s milk, and soy milk during single and consecutive swallows. Evaluations were performed jointly by a laryngologist and a speech-language pathologist (SLP). Outcome measures included the Penetration–Aspiration Scale (PAS) and the Yale Pharyngeal Residue Severity Rating Scale. Inter-rater reliability was assessed through blinded reassessment of 25% of examinations by an additional laryngologist and two SLPs. Results: Most swallows across all liquids were classified as safe. Unsafe PAS scores occurred numerically more frequently with cow’s milk (18.2–25.6%), than with water (6.9–11.6%) or soy milk (9.4–11.6%). For single swallows, a nominal overall difference across liquids was observed (Cochran’s Q = 6.00, p = 0.050), and for consecutive swallows an overall difference was also detected (Cochran’s Q = 8.00, p = 0.018). Pairwise comparisons were not statistically significant after correction for multiple testing. No statistically significant differences were identified between liquids for vallecular or pyriform sinus residue. Agreement in PAS scores across liquids ranged from low to moderate (κ = 0.291–0.609), and agreement for residue scores ranged from moderate to almost perfect (κ = 0.528–0.824). Inter-rater reliability was excellent (ICC = 0.93, 95% CI [0.90-0.95], p < 0.001). Conclusion: In this exploratory within-subject study, no statistically significant differences were observed in FEES penetration, aspiration, or pharyngeal residue scores when using water, cow’s milk, or soy milk. These findings provide preliminary descriptive data regarding the behavior of a commonly consumed plant-based liquid during FEES and may inform future research on liquid properties in swallowing assessment.