• Katarina Jennifer Ruscic, Janne Bøgh Stokholm, Johann Patlak, Hao Deng, Simons Jeroen Cedric Peter JCP, Timothy Houle, Jürgen Peters, and Matthias Eikermann.
• From the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (K.J.R., H.D., T.H.) Department of Anesthesiology, Herlev and Gentofte Hospital, Herlev, Denmark (J.B.S.) Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Hospital, Boston, Massachusetts (J.Patlak, M.E.) Helios Klinikum Krefeld, Klinik für Orthopädie, Unfall- und Handchirurgie, Krefeld, Germany (J.C.R.S.) Klinik für Anäesthesiologie und Intensivmedizin, Universität Duisburg Essen and Universitätsklinikum Essen, Essen, Germany (J.Peters, M.E.).
• Anesthesiology. 2018 Jul 1; 129 (1): 37-46.

BackgroundPropofol impairs upper airway dilator muscle tone and increases upper airway collapsibility. Preclinical studies show that carbon dioxide decreases propofol-mediated respiratory depression. We studied whether elevation of end-tidal carbon dioxide (PETCO2) via carbon dioxide insufflation reverses the airway collapsibility (primary hypothesis) and impaired genioglossus muscle electromyogram that accompany propofol anesthesia.MethodsWe present a prespecified, secondary analysis of previously published experiments in 12 volunteers breathing via a high-flow respiratory circuit used to control upper airway pressure under propofol anesthesia at two levels, with the deep level titrated to suppression of motor response. Ventilation, mask pressure, negative pharyngeal pressure, upper airway closing pressure, genioglossus electromyogram, bispectral index, and change in end-expiratory lung volume were measured as a function of elevation of PETCO2 above baseline and depth of propofol anesthesia.ResultsPETCO2 augmentation dose-dependently lowered upper airway closing pressure with a decrease of 3.1 cm H2O (95% CI, 2.2 to 3.9; P < 0.001) under deep anesthesia, indicating improved upper airway stability. In parallel, the phasic genioglossus electromyogram increased by 28% (23 to 34; P < 0.001). We found that genioglossus electromyogram activity was a significant modifier of the effect of PETCO2 elevation on closing pressure (P = 0.005 for interaction term).ConclusionsUpper airway collapsibility induced by propofol anesthesia can be reversed in a dose-dependent manner by insufflation of supplemental carbon dioxide. This effect is at least partly mediated by increased genioglossus muscle activity.

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