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By analyzing PSG data, anthropometric variables, and DISE results with CPAP titration levels, we can better understand possible mechanisms resulting in a higher CPAP titration level. We believe that the role of DISE can be expanded as a tool to identify the possible anatomical structures that may be corrected by oral appliance therapy or surgical intervention to improve CPAP compliance.

Objectives/Hypothesis This study aimed to assess the role of capnography in objectively evaluating breathing routes during drug‐induced sleep endoscopy (DISE) and further elucidate the relationship between breathing route, obstructive sleep apnea (OSA) severity, and DISE findings. Study Design Prospective observational study. Methods Nighty‐five patients with established OSA were recruited for this study from May 2017 to May 2019. DISE was performed in the operating room. Sedation was maintained with propofol using a target‐controlled infusion system and the depth of sedation was monitored based on the bispectral index. The breathing routes, which included oral breathing, oronasal breathing, and nasal breathing, were detected using capnography. DISE findings were recorded using the VOTE (velum, oropharynx, base of tongue, and epiglottis) classification. Results Patients with mouth breathing were associated with increased OSA severity, worse oximetric variables, and higher body mass index in comparison with those with other breathing routes. Mouth breathing was associated with a higher degree and higher prevalence of lateral pharyngeal wall collapse and tongue base collapse during DISE. Conclusions Mouth breathing was significantly associated with worse oxygen desaturation and increased degree of upper airway collapse. Therefore, patients with mouth breathing during propofol‐based intravenous anesthesia should be carefully monitored. Level of Evidence 4 Laryngoscope, 131:E659–E664, 2021

A significant discrepancy existed between retrolingual airway collapse evaluated by modified Mallampati score and Müller's maneuver. Modified Mallampati score is more correlated with DISE regarding retrolingual obstruction compared to Müller's maneuver. It should therefore be used as an initial evaluation of retrolingual obstruction when DISE is unavailable.