Thin Liquid Sip Sizes in Outpatient Adults with Normal and Disordered Swallowing: Modifying Factors and Relationships with Swallowing Safety and Efficiency

Introduction: Thin liquids are an important part of many swallowing assessment protocols, yet little is known about self-selected sip sizes in outpatient adults nor their relationship with functional swallowing outcomes. Therefore, this quality improvement study aimed to: (1) assess the influence of testing-specific factors on the size of self-selected sips in outpatient adults; (2) examine the relationships between self-selected sip sizes, patient characteristics, and degree of swallowing impairment; and (3) evaluate the relationship between the self-selected sip sizes, swallowing safety, and swallowing efficiency. Methods: Consecutive outpatient adults being evaluated for known or suspected swallowing impairments completed randomized self-selected sips of thin liquids varying by cup size, fill level, liquid color, liquid type, bolus delivery method, swallowing instruction, and endoscope presence. Self-selected sip sizes were measured for each trial. Multilevel statistical models were used to assess the relationships between self-selected sip size, testing conditions, patient characteristics, and pharyngeal residue, penetration, and aspiration as seen during flexible endoscopic evaluation of swallowing (FEES) and modified barium swallow studies (MBS). Results: Seventy-four outpatient adults were recruited, yielding an analysis of 595 self-selected sip sizes. The median self-selected sip size was 24.0 mL during the most natural drinking condition. Colored liquids, smaller amount of liquid filling a cup, and straw use significantly decreased sip size, whereas and transnasal endoscopy and barium significantly increased sip size (p < .05). Sex and height were the only patient characteristics significantly associated with sip size (p < .05). The size of self-selected sips of thin liquid was not associated with measures of pharyngeal residue, penetration, and aspiration (p > .05). Conclusion: Outpatient adults typically select thin liquid sips of ~24mL under natural conditions, similar to what is reported in healthy community dwelling adults and far exceeding sip sizes frequently used during routine clinical assessments. Testing-induced alterations significantly alter natural sip size, suggesting that “natural” self-selected sips during clinical assessments, FEES, and MBS rarely reflect real-world drinking. Because sip size is not predictable from patient characteristics and is altered when being testing, clinicians should consider testing a range of fixed volumes to comprehensively assess swallowing function across patients.