Silent aspiration risk is volume-dependent

Clinical swallow protocols cannot detect silent aspiration due to absence of overt behavioral signs, but screening with a much larger bolus volume, i.e., 90 cc vs. 1-10 cc, may elicit a reflexive cough in individuals who might otherwise exhibit silent aspiration. A swallow screen that maintains high sensitivity to identify aspiration risk while simultaneously reducing the false-negative rate for silent aspiration would be beneficial. The purpose of this study was to investigate whether silent aspiration risk was volume-dependent by using a 3-oz. (90-cc) water swallow challenge to elicit a reflexive cough when silent aspiration occurred on smaller bolus volumes. A prospective, consecutive, referral-based sample of 4102 inpatients from the acute-care setting of a large urban tertiary-care teaching hospital participated. Silent aspiration was determined first by fiberoptic endoscopy and then each participant was instructed to drink 3 oz. of water completely and without interruption. Criteria for challenge failure were inability to drink the entire amount, stopping and starting, or coughing and choking during or immediately after completion. Improved identification of aspiration risk status occurred for 58% of participants who exhibited silent aspiration on smaller volumes, i.e., an additional 48% of liquid silent aspirators and 65.6% of puree silent aspirators coughed when attempting the 3-oz. water swallow challenge. A low false-negative rate was observed for the entire population sample, i.e., ≤2.0%. A combined false-negative rate for participants who silently aspirated was 6.9%, i.e., 7.8% if silently aspirated liquid and 6.1% if silently aspirated puree consistency. Determination of silent aspiration risk was shown to be volume-dependent, with a larger volume eliciting a reflexive cough in individuals who previously silently aspirated on smaller volumes. A 3-oz. water swallow challenge's previously reported high sensitivity for identification of aspiration risk combined with the newly reported low false-negative rate mitigates the issue of silent aspiration risk during clinical swallow screening.