"Loose Lips Are Actually Good".

In Reply: We thank Drs. Zhou and Wang for their thoughtful comments on our study.1 Certainly, many factors may influence the tidal volume during anesthesia induction. We previously reported that progressive muscle paralysis induced by rocuronium injection did not change the tidal volume during facemask ventilation without airway maneuvers in adult subjects with normal upper airway anatomy.2 In contrast to Ikeda et al.’s study,2 the tidal volume progressively improved in both non–sleep disordered breathing and sleep disordered breathing groups in Sato et al.’s study.1 We believe there are three major differences between Ikeda et al.’s and Sato et al.’s study designs: anesthesia depth, initial airway patency, and airway maneuvers by the anesthetists. It is our opinion that anesthesia depth contributes little to time dependence of the tidal volume, given that pharyngeal collapsibility increases only slightly by increasing anesthesia depth with propofol, however, the pharyngeal (fig. 2) based on low expiratory flows and a blunted carbon dioxide trace. The study used an anesthesia mask that covered both the nose and mouth, so it is not possible to identify the source of the limited expiratory flow. This methodologic issue is important because it has the potential to obviate two of the authors’ conclusions: first, that partial expiratory obstruction exists, and second, that switching from oneto two-handed mask ventilation is the key move in normalizing ventilation. We did not observe partial expiratory obstruction in our study; it appeared to be an all-or-none phenomenon. In addition, chin lift and head tilt, maneuvers commonly employed in two-hand ventilation, did not relieve the obstruction. What did work was to allow the mouth to open between positive pressure breaths. An oral airway would provide similar benefit. These issues remain open, however, because we used simple observation rather than quantitative methods to determine the presence or absence of obstruction. We join with Sato et al. in calling for more detailed studies of the soft palate and surrounding pharynx in patients with expiratory obstruction.