• Olivia M D'Angelo, Daniel Diaz-Gil, Danuza Nunn, Jeroen C P Simons, Chloe Gianatasio, Noomi Mueller, Matthew J Meyer, Eric Pierce, Carl Rosow, and Matthias Eikermann.
• From the Department of Anesthesia, Critical Care, and Pain Medicine, Carl Rosow Clinical Research Center, Massachusetts General Hospital, Boston, Massachusetts (O.M.D., D.D.-G., J.C.P.S., C.G., N.M., M.J.M., E.P., C.R., M.E.); Department of Speech, Language, and Swallowing Disorders, Massachusetts General Hospital, Boston, Massachusetts (D.N.); and Universitätsklinikum Essen, Klinik für Anästhesie und Intensivmedizin, Essen, Germany (M.E.).
• Anesthesiology. 2014 Dec 1; 121 (6): 1175-83.

BackgroundCoordination between breathing and swallowing helps prevent aspiration of foreign material into the respiratory tract. The authors examined the effects of anesthesia and hypercapnia on swallowing-breathing coordination.MethodsIn a randomized controlled crossover study, general anesthesia with propofol or sevoflurane was titrated using an up-down method to identify the threshold for suppression of the motor response to electrical stimulation of the forearm. Additional measurements included bispectral index, genioglossus electromyogram, ventilation (pneumotachometer), and hypopharyngeal pressure. During wakefulness and at each level of anesthesia, carbon dioxide was added to increase the end-tidal pressure by 4 and 8 mmHg. A swallow was defined as increased genioglossus activity with deglutition apnea and an increase in hypopharyngeal pressure. Spontaneous swallows were categorized as physiological (during expiration or followed by expiration) or pathological (during inspiration or followed by an inspiration).ResultsA total of 224 swallows were analyzed. Anesthesia increased the proportion of pathological swallows (25.9% vs. 4.9%) and decreased the number of swallows per hour (1.7±3.3 vs. 28.0±22.3) compared to wakefulness. During anesthesia, hypercapnia decreased hypopharyngeal pressure during inspiration (-14.1±3.7 vs. -8.7±2 mmHg) and increased minute ventilation, the proportion of pathological swallows (19.1% vs. 12.3%), and the number of swallows per hour (5.5±17.0. vs. 1.3±5.5).ConclusionsAnesthesia impaired the coordination between swallowing and respiration. Mild hypercapnia increased the frequency of swallowing during anesthesia and the likelihood of pathological swallowing. During anesthesia, the risk for aspiration may be further increased when ventilatory drive is stimulated.

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